The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Anders M.n. Niklasson - One of the best experts on this subject based on the ideXlab platform.
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Higher-order symplectic Born-Oppenheimer molecular dynamics
2020Co-Authors: Anders M.n. Niklasson, Anders Odell, Nicolas Bock, Matt Challacombe, Anna Delin, Börje JohanssonAbstract:The extended Lagrangian formulation of time-reversible Born-Oppenheimer molecular dynamics (TR-BOMD) enables the use of geometric integrators in the propagation of both the nuclear and the electronic degrees of freedom on the Born-Oppenheimer potential energy surface. Different symplectic integrators up to the 6th order have been adapted and optimized to TR-BOMD in the framework of ab initio self-consistent-field theory. It is shown how the accuracy can be significantly improved compared to a conventional Verlet integration at the same level of computational cost, in particular for the case of very high accuracy requirements.
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Thermostating extended Lagrangian Born-Oppenheimer molecular dynamics.
Journal of Chemical Physics, 2015Co-Authors: Enrique Martínez, Marc J. Cawkwell, Arthur F. Voter, Anders M.n. NiklassonAbstract:Extended Lagrangian Born-Oppenheimer molecular dynamics is developed and analyzed for applications in canonical (NVT) simulations. Three different approaches are considered: the Nose and Andersen thermostats and Langevin dynamics. We have tested the temperature distribution under different conditions of self-consistent field (SCF) convergence and time step and compared the results to analytical predictions. We find that the simulations based on the extended Lagrangian Born-Oppenheimer framework provide accurate canonical distributions even under approximate SCF convergence, often requiring only a single diagonalization per time step, whereas regular Born-Oppenheimer formulations exhibit unphysical fluctuations unless a sufficiently high degree of convergence is reached at each time step. The thermostated extended Lagrangian framework thus offers an accurate approach to sample processes in the canonical ensemble at a fraction of the computational cost of regular Born-Oppenheimer molecular dynamics simulations.
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energy conserving linear scaling born Oppenheimer molecular dynamics
Journal of Chemical Physics, 2012Co-Authors: Marc J. Cawkwell, Anders M.n. NiklassonAbstract:Born-Oppenheimer molecular dynamics simulations with long-term conservation of the total energy and a computational cost that scales linearly with system size have been obtained simultaneously. Linear scaling with a low pre-factor is achieved using density matrix purification with sparse matrix algebra and a numerical threshold on matrix elements. The extended Lagrangian Born-Oppenheimer molecular dynamics formalism [A. M. N. Niklasson, Phys. Rev. Lett. 100, 123004 (2008)10.1103/PhysRevLett.100.123004] yields microcanonical trajectories with the approximate forces obtained from the linear scaling method that exhibit no systematic drift over hundreds of picoseconds and which are indistinguishable from trajectories computed using exact forces.
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wave function extended lagrangian born Oppenheimer molecular dynamics
Physical Review B, 2010Co-Authors: Peter Steneteg, Anders M.n. Niklasson, Igor A Abrikosov, Valery WeberAbstract:Extended Lagrangian Born-Oppenheimer molecular dynamics [A. M. N. Niklasson, Phys. Rev. Lett. 100, 123004 (2008)] has been generalized to the propagation of the electronic wave functions. The techn ...
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Higher-order symplectic integration in Born-Oppenheimer molecular dynamics
Journal of Chemical Physics, 2009Co-Authors: Anders Odell, Nicolas Bock, Matt Challacombe, Anna Delin, Börje Johansson, Anders M.n. NiklassonAbstract:The extended Lagrangian formulation of time-reversible Born-Oppenheimer molecular dynamics [A. M. N. Niklasson, C. J. Tymczak, and M. Challacombe, Phys. Rev. Lett. 100, 123004 (2008); Phys. Rev. Lett. 97, 123001 (2006)] enables the use of geometric integrators in the propagation of both the nuclear and the electronic degrees of freedom on the Born-Oppenheimer potential energy surface. Different symplectic integrators up to the sixth order have been adapted and optimized in the framework of ab initio self-consistent-field theory. It is shown how the accuracy can be significantly improved compared to a conventional Verlet integration at the same level of computational cost, in particular, for the case of very high accuracy requirements.
Matthias F Kling - One of the best experts on this subject based on the ideXlab platform.
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non born Oppenheimer molecular dynamics observed by coherent nuclear wave packets
Journal of Physical Chemistry Letters, 2020Co-Authors: Christian Burger, Myeongkee Park, Matthias F KlingAbstract:The reaction dynamics of a photochemical reaction is typically described by reaction coordinates based on the Born–Oppenheimer (BO) approximation. A strong interaction between electrons and nuclei,...
Kazuo Takatsuka - One of the best experts on this subject based on the ideXlab platform.
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Toward non‐Born–Oppenheimer quantum chemistry
International Journal of Quantum Chemistry, 2020Co-Authors: Kazuo TakatsukaAbstract:A practical quantum theory for unifying electronic and nuclear dynamics, which were separated by the Born–Oppenheimer approximation, is proposed. The theory consists of two processes. Nonadiabatic (quantum) electron wavepacket dynamics on branching (non-Born–Oppenheimer) nuclear paths are first constructed. Since these paths are not the classical trajectories, most of the existing semiclassical theories to generate quantum wavepacket do not work. Therefore, we apply our own developed semiclassical wavepacket theory to these generated non-Born–Oppenheimer paths. This wavepacket is generated based on what we call the action decomposed function, which does not require the information of the so-called stability matrix. Thus, the motion of nuclei is also quantized, and consequently the total wavefunction is represented as a series of entanglement between the electronic and nuclear wavepackets. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
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non born Oppenheimer quantum chemistry on the fly with continuous path branching due to nonadiabatic and intense optical interactions
Journal of Chemical Physics, 2010Co-Authors: Takehiro Yonehara, Kazuo TakatsukaAbstract:We extend our formerly proposed theory for non-Born–Oppenheimer electronic and nuclear wavepacket dynamics within on-the-fly scheme [T. Yonehara, S. Takahashi, and K. Takatsuka, J. Chem. Phys. 130, 214113 (2009)] to a case of nonadiabatic dynamics under an intense laser field: electron wavepacket in a molecule is propagated in attosecond time-scale along non-Born–Oppenheimer nuclear paths that smoothly branch due to nonadiabatic coupling and/or optical interactions. Such branching paths are determined consistently with the motion of the electron wavepackets. Furthermore, these nuclear paths are quantized in terms of Gaussian wavepackets (action decomposed function), which can be applied to nonclassical paths. Both electronic wavepacket dynamics and quantization of non-Born–Oppenheimer paths are generalized so as to include the direct effects of the classical vector potential of electromagnetic fields. In the second half of this paper, we perform numerical studies to explore nonadiabatic dynamics in a lase...
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non born Oppenheimer electronic and nuclear wavepacket dynamics
Journal of Chemical Physics, 2009Co-Authors: Takehiro Yonehara, Satoshi Takahashi, Kazuo TakatsukaAbstract:A practical quantum theory for unifying electronic and nuclear dynamics, which were separated by the Born–Oppenheimer approximation, is proposed. The theory consists of two processes. Nonadiabatic (quantum) electron wavepacket dynamics on branching (non-Born–Oppenheimer) nuclear paths are first constructed. Since these paths are not the classical trajectories, most of the existing semiclassical theories to generate quantum wavepacket do not work. Therefore, we apply our own developed semiclassical wavepacket theory to these generated non-Born–Oppenheimer paths. This wavepacket is generated based on what we call the action decomposed function, which does not require the information of the so-called stability matrix. Thus, the motion of nuclei is also quantized, and consequently the total wave function is represented as a series of entanglement between the electronic and nuclear wavepackets. In the last half of the article, we show the practice to demonstrate how these independent theories can be unified to...
Matthias Krack - One of the best experts on this subject based on the ideXlab platform.
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Static and dynamical properties of liquid water from First Principles by a Novel Car - Parrinello-like Approach
Journal of Chemical Theory …, 2009Co-Authors: TD KuÌhne, Matthias Krack, Michele ParrinelloAbstract:Using the recently developed Car−Parrinello-like approach to Born−Oppenheimer molecular dynamics ( Kühne, TD; et al. Phys. Rev. Lett. 2007, 98, 066401.), we assess the accuracy of ab initio molecular dynamics
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liquid water from first principles investigation of different sampling approaches
Journal of Physical Chemistry B, 2004Co-Authors: Christopher J Mundy, Matthew J Mcgrath, Ilja J Siepmann, Joost Vandevondele, Michiel Sprik, Jiirg Hutter, Bin Chen, Michael L Klein, Fawzi Mohamed, Matthias KrackAbstract:A series of first principles molecular dynamics and Monte Carlo simulations were carried out for liquid water to investigate the reproducibility of different sampling approaches. These simulations include Car−Parrinello molecular dynamics simulations using the program cpmd with different values of the fictitious electron mass in the microcanonical and canonical ensembles, Born−Oppenheimer molecular dynamics using the programs cpmd and cp2k in the microcanonical ensemble, and Metropolis Monte Carlo using cp2k in the canonical ensemble. With the exception of one simulation for 128 water molecules, all other simulations were carried out for systems consisting of 64 molecules. Although the simulations yield somewhat fortuitous agreement in structural properties, analysis of other properties demonstrate that one should exercise caution when assuming the reproducibility of Car−Parrinello and Born−Oppenheimer molecular dynamics simulations for small system sizes in the microcanonical ensemble. In contrast, the m...
Christian Burger - One of the best experts on this subject based on the ideXlab platform.
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non born Oppenheimer molecular dynamics observed by coherent nuclear wave packets
Journal of Physical Chemistry Letters, 2020Co-Authors: Christian Burger, Myeongkee Park, Matthias F KlingAbstract:The reaction dynamics of a photochemical reaction is typically described by reaction coordinates based on the Born–Oppenheimer (BO) approximation. A strong interaction between electrons and nuclei,...
