�ݺ�ߣshows by User: StephanIrle1

�ݺ�ߣshows by User: StephanIrle1 / http://www.slideshare.net/images/logo.gif �ݺ�ߣshows by User: StephanIrle1 / Mon, 26 Aug 2013 21:04:38 GMT �ݺ�ߣShare feed for �ݺ�ߣshows by User: StephanIrle1 Recent developments for the quantum chemical investigation of molecular systems with high structural complexity /StephanIrle1/structural-complexityapctcc6 structural-complexity-130826210439-phpapp02
The structural complexity of molecular clusters increases with size due to the associated, rapidly growing configuration space. Two examples are realized in i) the transition from molecular to bulk systems, and ii) in the subsequent chemical functionalization of nanomaterials. In such systems, traditional quantum chemical approaches of investigations are hampered by the vastly increasing computational cost, even considering ever-growing supercomputer capabilities. Computationally inexpensive, yet accurate schemes such as the density-functional tight-binding (DFTB) method promise here a significant advantage. We have recently engaged in developing novel methodologies for systems with increasing structural complexity, driven by motivation from experimental studies. In this presentation, we will briefly review a) our advances in the automatic parameterization of DFTB, and b) the Kick-fragment-based “CrazyLego” conformationally aware approach for studying molecular and ionic liquid clusters with increasing size.]]>
The structural complexity of molecular clusters increases with size due to the associated, rapidly growing configuration space. Two examples are realized in i) the transition from molecular to bulk systems, and ii) in the subsequent chemical functionalization of nanomaterials. In such systems, traditional quantum chemical approaches of investigations are hampered by the vastly increasing computational cost, even considering ever-growing supercomputer capabilities. Computationally inexpensive, yet accurate schemes such as the density-functional tight-binding (DFTB) method promise here a significant advantage. We have recently engaged in developing novel methodologies for systems with increasing structural complexity, driven by motivation from experimental studies. In this presentation, we will briefly review a) our advances in the automatic parameterization of DFTB, and b) the Kick-fragment-based “CrazyLego” conformationally aware approach for studying molecular and ionic liquid clusters with increasing size.]]> Mon, 26 Aug 2013 21:04:38 GMT /StephanIrle1/structural-complexityapctcc6 StephanIrle1@slideshare.net(StephanIrle1) Recent developments for the quantum chemical investigation of molecular systems with high structural complexity StephanIrle1 The structural complexity of molecular clusters increases with size due to the associated, rapidly growing configuration space. Two examples are realized in i) the transition from molecular to bulk systems, and ii) in the subsequent chemical functionalization of nanomaterials. In such systems, traditional quantum chemical approaches of investigations are hampered by the vastly increasing computational cost, even considering ever-growing supercomputer capabilities. Computationally inexpensive, yet accurate schemes such as the density-functional tight-binding (DFTB) method promise here a significant advantage. We have recently engaged in developing novel methodologies for systems with increasing structural complexity, driven by motivation from experimental studies. In this presentation, we will briefly review a) our advances in the automatic parameterization of DFTB, and b) the Kick-fragment-based “CrazyLego” conformationally aware approach for studying molecular and ionic liquid clusters with increasing size. <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/structural-complexity-130826210439-phpapp02-thumbnail.jpg?width=120&height=120&fit=bounds" /> The structural complexity of molecular clusters increases with size due to the associated, rapidly growing configuration space. Two examples are realized in i) the transition from molecular to bulk systems, and ii) in the subsequent chemical functionalization of nanomaterials. In such systems, traditional quantum chemical approaches of investigations are hampered by the vastly increasing computational cost, even considering ever-growing supercomputer capabilities. Computationally inexpensive, yet accurate schemes such as the density-functional tight-binding (DFTB) method promise here a significant advantage. We have recently engaged in developing novel methodologies for systems with increasing structural complexity, driven by motivation from experimental studies. In this presentation, we will briefly review a) our advances in the automatic parameterization of DFTB, and b) the Kick-fragment-based “CrazyLego” conformationally aware approach for studying molecular and ionic liquid clusters with increasing size.

Recent developments for the quantum chemical investigation of molecular systems with high structural complexity from Stephan Irle

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0 Density-Functional Tight-Binding (DFTB) as fast approximate DFT method - An introduction /slideshow/densityfunctional-tightbinding-dftb-as-fast-approximate-dft-method-an-introduction/23778227 dftb-talk-3427-130702051611-phpapp02
This presentation was given April 27, 2013 at Ibaraki University in Mito, Japan (Professor Seiji Mori's group). The presentation does not claim to give a complete overview of the complex field of DFTB parameterization, but rather focuses on the method's central approximations and discusses its performance in various applications.]]>
This presentation was given April 27, 2013 at Ibaraki University in Mito, Japan (Professor Seiji Mori's group). The presentation does not claim to give a complete overview of the complex field of DFTB parameterization, but rather focuses on the method's central approximations and discusses its performance in various applications.]]> Tue, 02 Jul 2013 05:16:10 GMT /slideshow/densityfunctional-tightbinding-dftb-as-fast-approximate-dft-method-an-introduction/23778227 StephanIrle1@slideshare.net(StephanIrle1) Density-Functional Tight-Binding (DFTB) as fast approximate DFT method - An introduction StephanIrle1 This presentation was given April 27, 2013 at Ibaraki University in Mito, Japan (Professor Seiji Mori's group). The presentation does not claim to give a complete overview of the complex field of DFTB parameterization, but rather focuses on the method's central approximations and discusses its performance in various applications. <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/dftb-talk-3427-130702051611-phpapp02-thumbnail.jpg?width=120&height=120&fit=bounds" /> This presentation was given April 27, 2013 at Ibaraki University in Mito, Japan (Professor Seiji Mori's group). The presentation does not claim to give a complete overview of the complex field of DFTB parameterization, but rather focuses on the method's central approximations and discusses its performance in various applications.

Density-Functional Tight-Binding (DFTB) as fast approximate DFT method - An introduction from Stephan Irle

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0 Haeckelite and Graphene Formation on a Metal Surface: Evidence for a Phase Transition at the Edge of Criticality /slideshow/mrs-s12graphenedynamicsforweb/23777358 mrs-s12-graphene-dynamics-for-web-130702044945-phpapp02
Quantum chemical molecular dynamics (QM/MD) simulations of ensembles of C2 molecules on the Ni(111) terrace show that, in the absence of a hexagonal template, hydrogen, or step edge, Haeckelite as a metastable intermediate is preferentially nucleated over graphene [1]. The nucleation process is dominated by the swift transition of long carbon chains towards a fully connected sp2 carbon network. Starting from a pentagon as nucleus, pentagons and heptagons condense during ring collapse reactions, which results in zero overall curvature. To the contrary, in the presence of a coronene-like C24 template, hexagonal ring formation is clearly promoted, in agreement with recent suggestions from experiments. In the absence of step edges or molecular templates, graphene nucleation follows Ostwald’s ‘rule of stages’ cascade of metastable states, from linear carbon chains, via Haeckelite islands that finally anneal to graphene. Furthermore, we found similarities between graphene nucleation and other critical phase transition phenomena [2]. Our analysis confirms the existence of a critical nC-C/NC value close to 1.0 (‘H’ model) and 1.1 (‘G’ model), where nC-C is the number of C-C bonds and NC is the number of carbon atoms. As in random graph theory, above this critical value, the further conversion of linear carbon chains to sp2 carbon polygons leads to the emergence of a fully networked carbon structure. Thus we find the theory of selforganized criticality [2] applicable to discuss the sp2 network formation from sp chains in the formation mechanism of graphenes. References: [1] Wang, Y.; Page, A. J.; Nishimoto, Y.; Qian, H.-J.; Morokuma, K., Irle, S.; JACS (just accepted) (2011). [2] Bak, P.; Tang, C.; Wiesenfeld, K., Phys. Rev. Lett. 1998, 59, 381.]]>
Quantum chemical molecular dynamics (QM/MD) simulations of ensembles of C2 molecules on the Ni(111) terrace show that, in the absence of a hexagonal template, hydrogen, or step edge, Haeckelite as a metastable intermediate is preferentially nucleated over graphene [1]. The nucleation process is dominated by the swift transition of long carbon chains towards a fully connected sp2 carbon network. Starting from a pentagon as nucleus, pentagons and heptagons condense during ring collapse reactions, which results in zero overall curvature. To the contrary, in the presence of a coronene-like C24 template, hexagonal ring formation is clearly promoted, in agreement with recent suggestions from experiments. In the absence of step edges or molecular templates, graphene nucleation follows Ostwald’s ‘rule of stages’ cascade of metastable states, from linear carbon chains, via Haeckelite islands that finally anneal to graphene. Furthermore, we found similarities between graphene nucleation and other critical phase transition phenomena [2]. Our analysis confirms the existence of a critical nC-C/NC value close to 1.0 (‘H’ model) and 1.1 (‘G’ model), where nC-C is the number of C-C bonds and NC is the number of carbon atoms. As in random graph theory, above this critical value, the further conversion of linear carbon chains to sp2 carbon polygons leads to the emergence of a fully networked carbon structure. Thus we find the theory of selforganized criticality [2] applicable to discuss the sp2 network formation from sp chains in the formation mechanism of graphenes. References: [1] Wang, Y.; Page, A. J.; Nishimoto, Y.; Qian, H.-J.; Morokuma, K., Irle, S.; JACS (just accepted) (2011). [2] Bak, P.; Tang, C.; Wiesenfeld, K., Phys. Rev. Lett. 1998, 59, 381.]]> Tue, 02 Jul 2013 04:49:45 GMT /slideshow/mrs-s12graphenedynamicsforweb/23777358 StephanIrle1@slideshare.net(StephanIrle1) Haeckelite and Graphene Formation on a Metal Surface: Evidence for a Phase Transition at the Edge of Criticality StephanIrle1 Quantum chemical molecular dynamics (QM/MD) simulations of ensembles of C2 molecules on the Ni(111) terrace show that, in the absence of a hexagonal template, hydrogen, or step edge, Haeckelite as a metastable intermediate is preferentially nucleated over graphene [1]. The nucleation process is dominated by the swift transition of long carbon chains towards a fully connected sp2 carbon network. Starting from a pentagon as nucleus, pentagons and heptagons condense during ring collapse reactions, which results in zero overall curvature. To the contrary, in the presence of a coronene-like C24 template, hexagonal ring formation is clearly promoted, in agreement with recent suggestions from experiments. In the absence of step edges or molecular templates, graphene nucleation follows Ostwald’s ‘rule of stages’ cascade of metastable states, from linear carbon chains, via Haeckelite islands that finally anneal to graphene. Furthermore, we found similarities between graphene nucleation and other critical phase transition phenomena [2]. Our analysis confirms the existence of a critical nC-C/NC value close to 1.0 (‘H’ model) and 1.1 (‘G’ model), where nC-C is the number of C-C bonds and NC is the number of carbon atoms. As in random graph theory, above this critical value, the further conversion of linear carbon chains to sp2 carbon polygons leads to the emergence of a fully networked carbon structure. Thus we find the theory of selforganized criticality [2] applicable to discuss the sp2 network formation from sp chains in the formation mechanism of graphenes. References: [1] Wang, Y.; Page, A. J.; Nishimoto, Y.; Qian, H.-J.; Morokuma, K., Irle, S.; JACS (just accepted) (2011). [2] Bak, P.; Tang, C.; Wiesenfeld, K., Phys. Rev. Lett. 1998, 59, 381. <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/mrs-s12-graphene-dynamics-for-web-130702044945-phpapp02-thumbnail.jpg?width=120&height=120&fit=bounds" /> Quantum chemical molecular dynamics (QM/MD) simulations of ensembles of C2 molecules on the Ni(111) terrace show that, in the absence of a hexagonal template, hydrogen, or step edge, Haeckelite as a metastable intermediate is preferentially nucleated over graphene [1]. The nucleation process is dominated by the swift transition of long carbon chains towards a fully connected sp2 carbon network. Starting from a pentagon as nucleus, pentagons and heptagons condense during ring collapse reactions, which results in zero overall curvature. To the contrary, in the presence of a coronene-like C24 template, hexagonal ring formation is clearly promoted, in agreement with recent suggestions from experiments. In the absence of step edges or molecular templates, graphene nucleation follows Ostwald’s ‘rule of stages’ cascade of metastable states, from linear carbon chains, via Haeckelite islands that finally anneal to graphene. Furthermore, we found similarities between graphene nucleation and other critical phase transition phenomena [2]. Our analysis confirms the existence of a critical nC-C/NC value close to 1.0 (‘H’ model) and 1.1 (‘G’ model), where nC-C is the number of C-C bonds and NC is the number of carbon atoms. As in random graph theory, above this critical value, the further conversion of linear carbon chains to sp2 carbon polygons leads to the emergence of a fully networked carbon structure. Thus we find the theory of selforganized criticality [2] applicable to discuss the sp2 network formation from sp chains in the formation mechanism of graphenes. References: [1] Wang, Y.; Page, A. J.; Nishimoto, Y.; Qian, H.-J.; Morokuma, K., Irle, S.; JACS (just accepted) (2011). [2] Bak, P.; Tang, C.; Wiesenfeld, K., Phys. Rev. Lett. 1998, 59, 381.

Haeckelite and Graphene Formation on a Metal Surface: Evidence for a Phase Transition at the Edge of Criticality from Stephan Irle

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0 Quantum chemical molecular dynamics simulations of graphene hydrogenation /slideshow/quantum-chemical-molecular-dynamics-simulations-of-graphene-hydrogenation/23777177 tachi-seminar-for-web-130702044520-phpapp02
Chemical adsorption of hydrogen atoms on graphite surfaces has attracted considerable interest due to its relevance for a broad range of areas including plasma/fusion physics, gap tuning in graphene, and hydrogen storage. We adjusted the C-H repulsive potential of the spin-polarized self-consistent-charge density-functional tight-binding (sSCC-DFTB) method to reproduce CCSD(T)-based relaxed potential energy curves for the attack of atomic hydrogen on a center carbon atom of pyrene and coronene at a tiny fraction of the computational cost. Using this cheap quantum chemical potential, we performed direct on-the-fly Born-Oppenheimer MD simulations while “shooting” H atoms with varying collision energies on a periodic graphene target equilibrated at 300 Kelvin. We compared reaction cross sections for a) elastic collisions, b) chemisorption reactions, c) penetration reactions in dependence of H/D/T kinetic energies, and found remarkable differences to previously reported classical MD simulations of the same process. Using the same potential, in simulations involving the shooting of up to 400 hydrogen atoms on the graphene sheet, we observed the self-assembly of C4H, a novel polymer with localized aromatic hexagons, in agreement with recent experimental findings.]]>
Chemical adsorption of hydrogen atoms on graphite surfaces has attracted considerable interest due to its relevance for a broad range of areas including plasma/fusion physics, gap tuning in graphene, and hydrogen storage. We adjusted the C-H repulsive potential of the spin-polarized self-consistent-charge density-functional tight-binding (sSCC-DFTB) method to reproduce CCSD(T)-based relaxed potential energy curves for the attack of atomic hydrogen on a center carbon atom of pyrene and coronene at a tiny fraction of the computational cost. Using this cheap quantum chemical potential, we performed direct on-the-fly Born-Oppenheimer MD simulations while “shooting” H atoms with varying collision energies on a periodic graphene target equilibrated at 300 Kelvin. We compared reaction cross sections for a) elastic collisions, b) chemisorption reactions, c) penetration reactions in dependence of H/D/T kinetic energies, and found remarkable differences to previously reported classical MD simulations of the same process. Using the same potential, in simulations involving the shooting of up to 400 hydrogen atoms on the graphene sheet, we observed the self-assembly of C4H, a novel polymer with localized aromatic hexagons, in agreement with recent experimental findings.]]> Tue, 02 Jul 2013 04:45:20 GMT /slideshow/quantum-chemical-molecular-dynamics-simulations-of-graphene-hydrogenation/23777177 StephanIrle1@slideshare.net(StephanIrle1) Quantum chemical molecular dynamics simulations of graphene hydrogenation StephanIrle1 Chemical adsorption of hydrogen atoms on graphite surfaces has attracted considerable interest due to its relevance for a broad range of areas including plasma/fusion physics, gap tuning in graphene, and hydrogen storage. We adjusted the C-H repulsive potential of the spin-polarized self-consistent-charge density-functional tight-binding (sSCC-DFTB) method to reproduce CCSD(T)-based relaxed potential energy curves for the attack of atomic hydrogen on a center carbon atom of pyrene and coronene at a tiny fraction of the computational cost. Using this cheap quantum chemical potential, we performed direct on-the-fly Born-Oppenheimer MD simulations while “shooting” H atoms with varying collision energies on a periodic graphene target equilibrated at 300 Kelvin. We compared reaction cross sections for a) elastic collisions, b) chemisorption reactions, c) penetration reactions in dependence of H/D/T kinetic energies, and found remarkable differences to previously reported classical MD simulations of the same process. Using the same potential, in simulations involving the shooting of up to 400 hydrogen atoms on the graphene sheet, we observed the self-assembly of C4H, a novel polymer with localized aromatic hexagons, in agreement with recent experimental findings. <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/tachi-seminar-for-web-130702044520-phpapp02-thumbnail.jpg?width=120&height=120&fit=bounds" /> Chemical adsorption of hydrogen atoms on graphite surfaces has attracted considerable interest due to its relevance for a broad range of areas including plasma/fusion physics, gap tuning in graphene, and hydrogen storage. We adjusted the C-H repulsive potential of the spin-polarized self-consistent-charge density-functional tight-binding (sSCC-DFTB) method to reproduce CCSD(T)-based relaxed potential energy curves for the attack of atomic hydrogen on a center carbon atom of pyrene and coronene at a tiny fraction of the computational cost. Using this cheap quantum chemical potential, we performed direct on-the-fly Born-Oppenheimer MD simulations while “shooting” H atoms with varying collision energies on a periodic graphene target equilibrated at 300 Kelvin. We compared reaction cross sections for a) elastic collisions, b) chemisorption reactions, c) penetration reactions in dependence of H/D/T kinetic energies, and found remarkable differences to previously reported classical MD simulations of the same process. Using the same potential, in simulations involving the shooting of up to 400 hydrogen atoms on the graphene sheet, we observed the self-assembly of C4H, a novel polymer with localized aromatic hexagons, in agreement with recent experimental findings.

Quantum chemical molecular dynamics simulations of graphene hydrogenation from Stephan Irle

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0 Kinetic Stability Governs Relative Fullerene Isomer Abundance /slideshow/fullerene-ksecs13forweb/23764963 fullerene-ks-ecs13-for-web-130701205935-phpapp02
A methodology to evaluate the kinetic stability of molecular nanostructures is presented based on the assumption of the independent and random nature of thermal vibrations, calculated at the density functional theory (DFT) level of theory using the harmonic approximation [1]. The kinetic stability (KS) is directly correlated to the cleavage probability for the weakest bond of a given molecular geometry. The application of the presented method to a selection of fullerenes (see Fig. 1) and carbon nanotubes yields clear correlation to their experimentally observed relative isomer abundances. Moreover, we present good agreement of harmonic vibrational eigenmodes between DFT and the computationally more efficient density-functional tight-binding (DFTB) method [2-4]. Thus, DFTB-based KS calculations allow the estimation of kinetic stability for more than 100,000 isomers of the fullerenes C20-C100. We found that the experimentally observed isomer abundances, as recorded for instance by mass spectroscopic investigations, are reasonably well reproduced by the Boltzmann-weighted kinetic stabilities of the cage isomers. This result suggests a mechanism of fullerene formation involving cage destruction, such as recently predicted by quantum chemical molecular dynamics (QM/MD) simulations [5-6]. Rerefences: [1] A. S. Fedorov et al., Phys. Rev. Lett., 107, 175506 (2011). [2] H. A. Witek et al., J. Chem. Phys., 121, 5163 (2004). [3] E. Małolepsza et al., Chem. Phys. Lett., 412, 237 (2005). [4] H. A. Witek et al., J. Chem. Phys., 125, 214706 (2006). [5] S. Irle et al., J. Phys. Chem. B, 110, 14531 (2006). [6] B. Saha et al., J. Phys. Chem. A, 115, 22707 (2011). ]]>
A methodology to evaluate the kinetic stability of molecular nanostructures is presented based on the assumption of the independent and random nature of thermal vibrations, calculated at the density functional theory (DFT) level of theory using the harmonic approximation [1]. The kinetic stability (KS) is directly correlated to the cleavage probability for the weakest bond of a given molecular geometry. The application of the presented method to a selection of fullerenes (see Fig. 1) and carbon nanotubes yields clear correlation to their experimentally observed relative isomer abundances. Moreover, we present good agreement of harmonic vibrational eigenmodes between DFT and the computationally more efficient density-functional tight-binding (DFTB) method [2-4]. Thus, DFTB-based KS calculations allow the estimation of kinetic stability for more than 100,000 isomers of the fullerenes C20-C100. We found that the experimentally observed isomer abundances, as recorded for instance by mass spectroscopic investigations, are reasonably well reproduced by the Boltzmann-weighted kinetic stabilities of the cage isomers. This result suggests a mechanism of fullerene formation involving cage destruction, such as recently predicted by quantum chemical molecular dynamics (QM/MD) simulations [5-6]. Rerefences: [1] A. S. Fedorov et al., Phys. Rev. Lett., 107, 175506 (2011). [2] H. A. Witek et al., J. Chem. Phys., 121, 5163 (2004). [3] E. Małolepsza et al., Chem. Phys. Lett., 412, 237 (2005). [4] H. A. Witek et al., J. Chem. Phys., 125, 214706 (2006). [5] S. Irle et al., J. Phys. Chem. B, 110, 14531 (2006). [6] B. Saha et al., J. Phys. Chem. A, 115, 22707 (2011). ]]> Mon, 01 Jul 2013 20:59:35 GMT /slideshow/fullerene-ksecs13forweb/23764963 StephanIrle1@slideshare.net(StephanIrle1) Kinetic Stability Governs Relative Fullerene Isomer Abundance StephanIrle1 A methodology to evaluate the kinetic stability of molecular nanostructures is presented based on the assumption of the independent and random nature of thermal vibrations, calculated at the density functional theory (DFT) level of theory using the harmonic approximation [1]. The kinetic stability (KS) is directly correlated to the cleavage probability for the weakest bond of a given molecular geometry. The application of the presented method to a selection of fullerenes (see Fig. 1) and carbon nanotubes yields clear correlation to their experimentally observed relative isomer abundances. Moreover, we present good agreement of harmonic vibrational eigenmodes between DFT and the computationally more efficient density-functional tight-binding (DFTB) method [2-4]. Thus, DFTB-based KS calculations allow the estimation of kinetic stability for more than 100,000 isomers of the fullerenes C20-C100. We found that the experimentally observed isomer abundances, as recorded for instance by mass spectroscopic investigations, are reasonably well reproduced by the Boltzmann-weighted kinetic stabilities of the cage isomers. This result suggests a mechanism of fullerene formation involving cage destruction, such as recently predicted by quantum chemical molecular dynamics (QM/MD) simulations [5-6]. Rerefences: [1] A. S. Fedorov et al., Phys. Rev. Lett., 107, 175506 (2011). [2] H. A. Witek et al., J. Chem. Phys., 121, 5163 (2004). [3] E. Małolepsza et al., Chem. Phys. Lett., 412, 237 (2005). [4] H. A. Witek et al., J. Chem. Phys., 125, 214706 (2006). [5] S. Irle et al., J. Phys. Chem. B, 110, 14531 (2006). [6] B. Saha et al., J. Phys. Chem. A, 115, 22707 (2011). <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/fullerene-ks-ecs13-for-web-130701205935-phpapp02-thumbnail.jpg?width=120&height=120&fit=bounds" /> A methodology to evaluate the kinetic stability of molecular nanostructures is presented based on the assumption of the independent and random nature of thermal vibrations, calculated at the density functional theory (DFT) level of theory using the harmonic approximation [1]. The kinetic stability (KS) is directly correlated to the cleavage probability for the weakest bond of a given molecular geometry. The application of the presented method to a selection of fullerenes (see Fig. 1) and carbon nanotubes yields clear correlation to their experimentally observed relative isomer abundances. Moreover, we present good agreement of harmonic vibrational eigenmodes between DFT and the computationally more efficient density-functional tight-binding (DFTB) method [2-4]. Thus, DFTB-based KS calculations allow the estimation of kinetic stability for more than 100,000 isomers of the fullerenes C20-C100. We found that the experimentally observed isomer abundances, as recorded for instance by mass spectroscopic investigations, are reasonably well reproduced by the Boltzmann-weighted kinetic stabilities of the cage isomers. This result suggests a mechanism of fullerene formation involving cage destruction, such as recently predicted by quantum chemical molecular dynamics (QM/MD) simulations [5-6]. Rerefences: [1] A. S. Fedorov et al., Phys. Rev. Lett., 107, 175506 (2011). [2] H. A. Witek et al., J. Chem. Phys., 121, 5163 (2004). [3] E. Małolepsza et al., Chem. Phys. Lett., 412, 237 (2005). [4] H. A. Witek et al., J. Chem. Phys., 125, 214706 (2006). [5] S. Irle et al., J. Phys. Chem. B, 110, 14531 (2006). [6] B. Saha et al., J. Phys. Chem. A, 115, 22707 (2011).

Kinetic Stability Governs Relative Fullerene Isomer Abundance from Stephan Irle

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0 What can we learn from molecular dynamics simulations of carbon nanotube and graphene growth? /slideshow/what-can-we-learn-from-molecular-dynamics-simulations-of-carbon-nanotube-and-graphene-growth/23762047 ding-md-for-cnt-graphene-growth-130701191703-phpapp01
We present the results of nonequilibrium molecular dynamics (MD) simulations of catalytic and non-catalytic carbon nanostructure formation processes, including single-walled carbon nanotube (SWCNT) and graphene nucleation and growth. In the talk, we discuss the significance of the findings in the light of more traditional, static descriptions of growth reaction mechanisms, and highlight differences as well as commonalities.]]>
We present the results of nonequilibrium molecular dynamics (MD) simulations of catalytic and non-catalytic carbon nanostructure formation processes, including single-walled carbon nanotube (SWCNT) and graphene nucleation and growth. In the talk, we discuss the significance of the findings in the light of more traditional, static descriptions of growth reaction mechanisms, and highlight differences as well as commonalities.]]> Mon, 01 Jul 2013 19:17:03 GMT /slideshow/what-can-we-learn-from-molecular-dynamics-simulations-of-carbon-nanotube-and-graphene-growth/23762047 StephanIrle1@slideshare.net(StephanIrle1) What can we learn from molecular dynamics simulations of carbon nanotube and graphene growth? StephanIrle1 We present the results of nonequilibrium molecular dynamics (MD) simulations of catalytic and non-catalytic carbon nanostructure formation processes, including single-walled carbon nanotube (SWCNT) and graphene nucleation and growth. In the talk, we discuss the significance of the findings in the light of more traditional, static descriptions of growth reaction mechanisms, and highlight differences as well as commonalities. <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/ding-md-for-cnt-graphene-growth-130701191703-phpapp01-thumbnail.jpg?width=120&height=120&fit=bounds" /> We present the results of nonequilibrium molecular dynamics (MD) simulations of catalytic and non-catalytic carbon nanostructure formation processes, including single-walled carbon nanotube (SWCNT) and graphene nucleation and growth. In the talk, we discuss the significance of the findings in the light of more traditional, static descriptions of growth reaction mechanisms, and highlight differences as well as commonalities.

What can we learn from molecular dynamics simulations of carbon nanotube and graphene growth? from Stephan Irle

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0 SWCNT Growth from Chiral and Achiral Carbon Nanorings: Prediction of Chirality and Diameter Influence on Local Growth Rates /slideshow/swcnt-growth-from-chiral-and-achiral-carbon-nanorings-prediction-of-chirality-and-diameter-influence-on-local-growth-rates/23759813 cpp-growth-nasa-for-carl-130701180552-phpapp01
Catalyst-free, chirality-controlled growth of chiral and achiral single-walled carbon nanotubes (SWCNTs) from organic precursors is demonstrated using quantum chemical simulations [1]. Growth of (4,3), (6,5), (6,1), (10,1), (6,6) and (8,0) SWCNTs was induced by ethynyl radical (C2H) addition to organic precursors. These simulations show a strong dependence of the SWCNT growth rate on the chiral angle, θ. The SWCNT diameter however does not influence the SWCNT growth rate under these conditions. This agreement with a previously proposed screw-dislocation-like model of transition metal-catalyzed SWCNT growth rates [2] indicates that the SWCNT growth rate is an intrinsic property of the SWCNT edge itself. Conversely, we predict that the rate of local SWCNT growth via Diels-Alder cycloaddition of C2H2 is strongly influenced by the diameter of the SWCNT. We therefore predict the existence of a maximum local growth rate for an optimum diameter/chirality combination at a given C2H/C2H2 ratio. We also find that the ability of a SWCNT to avoid defect formation during growth is an intrinsic quality of the SWCNT edge. References: [1] Li, H.-B.; Page, A. J.; Irle, S.; Morokuma, K. J. Am. Chem. Soc. 2012, 134, 15887-15896. [2] Ding, F.; Harutyunyan, A. R.; Yakobson, B. I. Proc. Natl. Acad. Sci. 2009, 106, 2506-2509. ]]>
Catalyst-free, chirality-controlled growth of chiral and achiral single-walled carbon nanotubes (SWCNTs) from organic precursors is demonstrated using quantum chemical simulations [1]. Growth of (4,3), (6,5), (6,1), (10,1), (6,6) and (8,0) SWCNTs was induced by ethynyl radical (C2H) addition to organic precursors. These simulations show a strong dependence of the SWCNT growth rate on the chiral angle, θ. The SWCNT diameter however does not influence the SWCNT growth rate under these conditions. This agreement with a previously proposed screw-dislocation-like model of transition metal-catalyzed SWCNT growth rates [2] indicates that the SWCNT growth rate is an intrinsic property of the SWCNT edge itself. Conversely, we predict that the rate of local SWCNT growth via Diels-Alder cycloaddition of C2H2 is strongly influenced by the diameter of the SWCNT. We therefore predict the existence of a maximum local growth rate for an optimum diameter/chirality combination at a given C2H/C2H2 ratio. We also find that the ability of a SWCNT to avoid defect formation during growth is an intrinsic quality of the SWCNT edge. References: [1] Li, H.-B.; Page, A. J.; Irle, S.; Morokuma, K. J. Am. Chem. Soc. 2012, 134, 15887-15896. [2] Ding, F.; Harutyunyan, A. R.; Yakobson, B. I. Proc. Natl. Acad. Sci. 2009, 106, 2506-2509. ]]> Mon, 01 Jul 2013 18:05:52 GMT /slideshow/swcnt-growth-from-chiral-and-achiral-carbon-nanorings-prediction-of-chirality-and-diameter-influence-on-local-growth-rates/23759813 StephanIrle1@slideshare.net(StephanIrle1) SWCNT Growth from Chiral and Achiral Carbon Nanorings: Prediction of Chirality and Diameter Influence on Local Growth Rates StephanIrle1 Catalyst-free, chirality-controlled growth of chiral and achiral single-walled carbon nanotubes (SWCNTs) from organic precursors is demonstrated using quantum chemical simulations [1]. Growth of (4,3), (6,5), (6,1), (10,1), (6,6) and (8,0) SWCNTs was induced by ethynyl radical (C2H) addition to organic precursors. These simulations show a strong dependence of the SWCNT growth rate on the chiral angle, θ. The SWCNT diameter however does not influence the SWCNT growth rate under these conditions. This agreement with a previously proposed screw-dislocation-like model of transition metal-catalyzed SWCNT growth rates [2] indicates that the SWCNT growth rate is an intrinsic property of the SWCNT edge itself. Conversely, we predict that the rate of local SWCNT growth via Diels-Alder cycloaddition of C2H2 is strongly influenced by the diameter of the SWCNT. We therefore predict the existence of a maximum local growth rate for an optimum diameter/chirality combination at a given C2H/C2H2 ratio. We also find that the ability of a SWCNT to avoid defect formation during growth is an intrinsic quality of the SWCNT edge. References: [1] Li, H.-B.; Page, A. J.; Irle, S.; Morokuma, K. J. Am. Chem. Soc. 2012, 134, 15887-15896. [2] Ding, F.; Harutyunyan, A. R.; Yakobson, B. I. Proc. Natl. Acad. Sci. 2009, 106, 2506-2509. <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/cpp-growth-nasa-for-carl-130701180552-phpapp01-thumbnail.jpg?width=120&height=120&fit=bounds" /> Catalyst-free, chirality-controlled growth of chiral and achiral single-walled carbon nanotubes (SWCNTs) from organic precursors is demonstrated using quantum chemical simulations [1]. Growth of (4,3), (6,5), (6,1), (10,1), (6,6) and (8,0) SWCNTs was induced by ethynyl radical (C2H) addition to organic precursors. These simulations show a strong dependence of the SWCNT growth rate on the chiral angle, θ. The SWCNT diameter however does not influence the SWCNT growth rate under these conditions. This agreement with a previously proposed screw-dislocation-like model of transition metal-catalyzed SWCNT growth rates [2] indicates that the SWCNT growth rate is an intrinsic property of the SWCNT edge itself. Conversely, we predict that the rate of local SWCNT growth via Diels-Alder cycloaddition of C2H2 is strongly influenced by the diameter of the SWCNT. We therefore predict the existence of a maximum local growth rate for an optimum diameter/chirality combination at a given C2H/C2H2 ratio. We also find that the ability of a SWCNT to avoid defect formation during growth is an intrinsic quality of the SWCNT edge. References: [1] Li, H.-B.; Page, A. J.; Irle, S.; Morokuma, K. J. Am. Chem. Soc. 2012, 134, 15887-15896. [2] Ding, F.; Harutyunyan, A. R.; Yakobson, B. I. Proc. Natl. Acad. Sci. 2009, 106, 2506-2509.

SWCNT Growth from Chiral and Achiral Carbon Nanorings: Prediction of Chirality and Diameter Influence on Local Growth Rates from Stephan Irle

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0 Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes /slideshow/origin-of-the-sizedependent-fluorescence-blueshift-in-ncycloparaphenylenes/23759587 excited-states-130701175756-phpapp01
We present quantum chemical electronic structure calculations to investigate the nature of the low-lying excited states of [n]cycloparaphenylenes ([n]CPPs) and the role of static and dynamic geometrical distortions in the bright states. The lowest-energy bright states involve single-electron excitations from S0 ground state to S2 and S3 states, which are at the Franck-Condon geometry the two components of a twofold degenerate 1E state. They couple to a twofold degenerate e vibration which induces Jahn-Teller (JT) deformation of the CPP geometry from circular to oval shape. Non-radiative decay from the S2/S3 states to the ground S0 and first excited, dark S1 states is suppressed due to symmetry rules. The emission spectral features in CPPs with large number of phenylene units n can therefore largely be attributed to the E ⊗ e JT system associated with S2 and S3. However, absorption and emission energies computed at the respective S0 and S2/S3 minimum energy geometries are found to be nearly identical, independent of the molecular size n in the CPP molecules. In contrast, molecular dynamics simulations performed on the excited state potential surfaces are able to explain the experimentally observed fluorescence blueshift of the strongest emission peaks with increasing molecular size. This unusual feature turns out to be a consequence of large vibrational amplitudes in small [n]CPPs, causing greater Stokes shifts, while large [n]CPPs are more rigid and therefore feature smaller Stokes shifts (“dynamic blueshift”). For the same reasons, symmetry rules are violated to a greater extent in small [n]CPPs, and it is expected that in their case a “static blueshift” due to emission from S1 contributes in the fluorescence spectra. ]]>
We present quantum chemical electronic structure calculations to investigate the nature of the low-lying excited states of [n]cycloparaphenylenes ([n]CPPs) and the role of static and dynamic geometrical distortions in the bright states. The lowest-energy bright states involve single-electron excitations from S0 ground state to S2 and S3 states, which are at the Franck-Condon geometry the two components of a twofold degenerate 1E state. They couple to a twofold degenerate e vibration which induces Jahn-Teller (JT) deformation of the CPP geometry from circular to oval shape. Non-radiative decay from the S2/S3 states to the ground S0 and first excited, dark S1 states is suppressed due to symmetry rules. The emission spectral features in CPPs with large number of phenylene units n can therefore largely be attributed to the E ⊗ e JT system associated with S2 and S3. However, absorption and emission energies computed at the respective S0 and S2/S3 minimum energy geometries are found to be nearly identical, independent of the molecular size n in the CPP molecules. In contrast, molecular dynamics simulations performed on the excited state potential surfaces are able to explain the experimentally observed fluorescence blueshift of the strongest emission peaks with increasing molecular size. This unusual feature turns out to be a consequence of large vibrational amplitudes in small [n]CPPs, causing greater Stokes shifts, while large [n]CPPs are more rigid and therefore feature smaller Stokes shifts (“dynamic blueshift”). For the same reasons, symmetry rules are violated to a greater extent in small [n]CPPs, and it is expected that in their case a “static blueshift” due to emission from S1 contributes in the fluorescence spectra. ]]> Mon, 01 Jul 2013 17:57:56 GMT /slideshow/origin-of-the-sizedependent-fluorescence-blueshift-in-ncycloparaphenylenes/23759587 StephanIrle1@slideshare.net(StephanIrle1) Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes StephanIrle1 We present quantum chemical electronic structure calculations to investigate the nature of the low-lying excited states of [n]cycloparaphenylenes ([n]CPPs) and the role of static and dynamic geometrical distortions in the bright states. The lowest-energy bright states involve single-electron excitations from S0 ground state to S2 and S3 states, which are at the Franck-Condon geometry the two components of a twofold degenerate 1E state. They couple to a twofold degenerate e vibration which induces Jahn-Teller (JT) deformation of the CPP geometry from circular to oval shape. Non-radiative decay from the S2/S3 states to the ground S0 and first excited, dark S1 states is suppressed due to symmetry rules. The emission spectral features in CPPs with large number of phenylene units n can therefore largely be attributed to the E ⊗ e JT system associated with S2 and S3. However, absorption and emission energies computed at the respective S0 and S2/S3 minimum energy geometries are found to be nearly identical, independent of the molecular size n in the CPP molecules. In contrast, molecular dynamics simulations performed on the excited state potential surfaces are able to explain the experimentally observed fluorescence blueshift of the strongest emission peaks with increasing molecular size. This unusual feature turns out to be a consequence of large vibrational amplitudes in small [n]CPPs, causing greater Stokes shifts, while large [n]CPPs are more rigid and therefore feature smaller Stokes shifts (“dynamic blueshift”). For the same reasons, symmetry rules are violated to a greater extent in small [n]CPPs, and it is expected that in their case a “static blueshift” due to emission from S1 contributes in the fluorescence spectra. <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/excited-states-130701175756-phpapp01-thumbnail.jpg?width=120&height=120&fit=bounds" /> We present quantum chemical electronic structure calculations to investigate the nature of the low-lying excited states of [n]cycloparaphenylenes ([n]CPPs) and the role of static and dynamic geometrical distortions in the bright states. The lowest-energy bright states involve single-electron excitations from S0 ground state to S2 and S3 states, which are at the Franck-Condon geometry the two components of a twofold degenerate 1E state. They couple to a twofold degenerate e vibration which induces Jahn-Teller (JT) deformation of the CPP geometry from circular to oval shape. Non-radiative decay from the S2/S3 states to the ground S0 and first excited, dark S1 states is suppressed due to symmetry rules. The emission spectral features in CPPs with large number of phenylene units n can therefore largely be attributed to the E ⊗ e JT system associated with S2 and S3. However, absorption and emission energies computed at the respective S0 and S2/S3 minimum energy geometries are found to be nearly identical, independent of the molecular size n in the CPP molecules. In contrast, molecular dynamics simulations performed on the excited state potential surfaces are able to explain the experimentally observed fluorescence blueshift of the strongest emission peaks with increasing molecular size. This unusual feature turns out to be a consequence of large vibrational amplitudes in small [n]CPPs, causing greater Stokes shifts, while large [n]CPPs are more rigid and therefore feature smaller Stokes shifts (“dynamic blueshift”). For the same reasons, symmetry rules are violated to a greater extent in small [n]CPPs, and it is expected that in their case a “static blueshift” due to emission from S1 contributes in the fluorescence spectra.

Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes from Stephan Irle

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0 Rh(I)-catalyzed Aldol-type Reaction of Organonitriles under Mild Conditions: Theoretical Investigations /slideshow/ibarakirh-aldolforweb/23758876 ibaraki-rh-aldol-for-web-130701173612-phpapp02
Chemical modification of nitrle groups has significant importance in the field of organic synthesis. In particular, aldol-type reactions of organonitriles with aldehydes provide β-hydroxynitries, which are potential precursors for pharmaceutically important functionality. We previously reported that RhI complexes efficiently catalyzed aldol-type reactions of nitriles under mild conditions. However, the mechanism for activation of nitrile group in this Rh catalysis was not made clear. Because of the difficulty in functionalizing the nitrile group, it is of great importance to elucidate the mechanism of such an efficient catalytic reaction. Here, we conducted theoretical investigations to clarify the mechanism for the Rh catalysis. All structures were optimized using the density functional theory (DFT) with the B3PW91 functional. We chose a moderate basis set size (6-31G(d) for non-metal elements and LanL2DZ for Rh) for geometry optimization, and energy refinement was done using a larger basis set ((aug-)cc-pVTZ and ECP28MWB) at ONIOM(DF-LCCSD(T):DF-LMP2). We looked into several reaction pathways with monomer and dimer catalysts, and proposed a plausible catalytic cycle.]]>
Chemical modification of nitrle groups has significant importance in the field of organic synthesis. In particular, aldol-type reactions of organonitriles with aldehydes provide β-hydroxynitries, which are potential precursors for pharmaceutically important functionality. We previously reported that RhI complexes efficiently catalyzed aldol-type reactions of nitriles under mild conditions. However, the mechanism for activation of nitrile group in this Rh catalysis was not made clear. Because of the difficulty in functionalizing the nitrile group, it is of great importance to elucidate the mechanism of such an efficient catalytic reaction. Here, we conducted theoretical investigations to clarify the mechanism for the Rh catalysis. All structures were optimized using the density functional theory (DFT) with the B3PW91 functional. We chose a moderate basis set size (6-31G(d) for non-metal elements and LanL2DZ for Rh) for geometry optimization, and energy refinement was done using a larger basis set ((aug-)cc-pVTZ and ECP28MWB) at ONIOM(DF-LCCSD(T):DF-LMP2). We looked into several reaction pathways with monomer and dimer catalysts, and proposed a plausible catalytic cycle.]]> Mon, 01 Jul 2013 17:36:12 GMT /slideshow/ibarakirh-aldolforweb/23758876 StephanIrle1@slideshare.net(StephanIrle1) Rh(I)-catalyzed Aldol-type Reaction of Organonitriles under Mild Conditions: Theoretical Investigations StephanIrle1 Chemical modification of nitrle groups has significant importance in the field of organic synthesis. In particular, aldol-type reactions of organonitriles with aldehydes provide β-hydroxynitries, which are potential precursors for pharmaceutically important functionality. We previously reported that RhI complexes efficiently catalyzed aldol-type reactions of nitriles under mild conditions. However, the mechanism for activation of nitrile group in this Rh catalysis was not made clear. Because of the difficulty in functionalizing the nitrile group, it is of great importance to elucidate the mechanism of such an efficient catalytic reaction. Here, we conducted theoretical investigations to clarify the mechanism for the Rh catalysis. All structures were optimized using the density functional theory (DFT) with the B3PW91 functional. We chose a moderate basis set size (6-31G(d) for non-metal elements and LanL2DZ for Rh) for geometry optimization, and energy refinement was done using a larger basis set ((aug-)cc-pVTZ and ECP28MWB) at ONIOM(DF-LCCSD(T):DF-LMP2). We looked into several reaction pathways with monomer and dimer catalysts, and proposed a plausible catalytic cycle. <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/ibaraki-rh-aldol-for-web-130701173612-phpapp02-thumbnail.jpg?width=120&height=120&fit=bounds" /> Chemical modification of nitrle groups has significant importance in the field of organic synthesis. In particular, aldol-type reactions of organonitriles with aldehydes provide β-hydroxynitries, which are potential precursors for pharmaceutically important functionality. We previously reported that RhI complexes efficiently catalyzed aldol-type reactions of nitriles under mild conditions. However, the mechanism for activation of nitrile group in this Rh catalysis was not made clear. Because of the difficulty in functionalizing the nitrile group, it is of great importance to elucidate the mechanism of such an efficient catalytic reaction. Here, we conducted theoretical investigations to clarify the mechanism for the Rh catalysis. All structures were optimized using the density functional theory (DFT) with the B3PW91 functional. We chose a moderate basis set size (6-31G(d) for non-metal elements and LanL2DZ for Rh) for geometry optimization, and energy refinement was done using a larger basis set ((aug-)cc-pVTZ and ECP28MWB) at ONIOM(DF-LCCSD(T):DF-LMP2). We looked into several reaction pathways with monomer and dimer catalysts, and proposed a plausible catalytic cycle.

Rh(I)-catalyzed Aldol-type Reaction of Organonitriles under Mild Conditions: Theoretical Investigations from Stephan Irle

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0 https://cdn.slidesharecdn.com/profile-photo-StephanIrle1-48x48.jpg?cb=1712754948 Stephan Irle has performed research in computational chemistry and materials sciences in Germany, Austria, the United States, and Japan. He has been a founding principal investigator at the Institute of Transformative Bio-Molecules (WPI-ITbM) at Nagoya University and member of the Japanese “post-K supercomputer” support project. His specialty is the quantum chemical study of complex systems. Target areas are soft matter and biosimulations, excited states of large molecules, and catalysis. Complementary studies of physicochemical properties, theoretical spectroscopy, and the development of methodologies including approximate quantum chemical methods accompany this research. www.ornl.gov/staff-profile/stephan-irle https://cdn.slidesharecdn.com/ss_thumbnails/structural-complexity-130826210439-phpapp02-thumbnail.jpg?width=320&height=320&fit=bounds StephanIrle1/structural-complexityapctcc6 Recent developments fo... https://cdn.slidesharecdn.com/ss_thumbnails/dftb-talk-3427-130702051611-phpapp02-thumbnail.jpg?width=320&height=320&fit=bounds slideshow/densityfunctional-tightbinding-dftb-as-fast-approximate-dft-method-an-introduction/23778227 Density-Functional Tig... https://cdn.slidesharecdn.com/ss_thumbnails/mrs-s12-graphene-dynamics-for-web-130702044945-phpapp02-thumbnail.jpg?width=320&height=320&fit=bounds slideshow/mrs-s12graphenedynamicsforweb/23777358 Haeckelite and Graphen...