The Experts below are selected from a list of 49221 Experts worldwide ranked by ideXlab platform
George H. Booth - One of the best experts on this subject based on the ideXlab platform.
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analytic nuclear forces and molecular properties from full configuration interaction quantum monte carlo
Journal of Chemical Physics, 2015Co-Authors: Robert E Thomas, Catherine Overy, George H. Booth, Ali Alavi, Peter J. Knowles, Daniel OpalkaAbstract:Unbiased stochastic sampling of the one- and two-body reduced density matrices is achieved in full configuration interaction quantum Monte Carlo with the introduction of a second, “replica” ensemble of walkers, whose population evolves in imaginary time independently from the first and which entails only modest additional computational overheads. The matrices obtained from this approach are shown to be representative of full configuration-interaction quality and hence provide a realistic opportunity to achieve high-quality results for a range of properties whose operators do not necessarily commute with the Hamiltonian. A density-matrix formulated quasi-Variational Energy estimator having been already proposed and investigated, the present work extends the scope of the theory to take in studies of analytic nuclear forces, molecular dipole moments, and polarisabilities, with extensive comparison to exact results where possible. These new results confirm the suitability of the sampling technique and, where sufficiently large basis sets are available, achieve close agreement with experimental values, expanding the scope of the method to new areas of investigation.
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Unbiased reduced density matrices and electronic properties from full configuration interaction quantum Monte Carlo
The Journal of Chemical Physics, 2014Co-Authors: Catherine Overy, N. S. Blunt, Deidre Cleland, George H. Booth, James J Shepherd, Ali AlaviAbstract:Properties that are necessarily formulated within pure (symmetric) expectation values are difficult to calculate for projector quantum Monte Carlo approaches, but are critical in order to compute many of the important observable properties of electronic systems. Here, we investigate an approach for the sampling of unbiased reduced density matrices within the full configuration interaction quantum Monte Carlo dynamic, which requires only small computational overheads. This is achieved via an independent replica population of walkers in the dynamic, sampled alongside the original population. The resulting reduced density matrices are free from systematic error (beyond those present via con- straints on the dynamic itself) and can be used to compute a variety of expectation values and properties, with rapid convergence to an exact limit.Aquasi-Variational Energy estimate derived from these density matrices is proposed as an accurate alternative to the projected estimator for multiconfigurational wavefunctions, while its Variational property could potentially lend itself to accurate extrapolation approaches in larger systems.
Ali Alavi - One of the best experts on this subject based on the ideXlab platform.
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analytic nuclear forces and molecular properties from full configuration interaction quantum monte carlo
Journal of Chemical Physics, 2015Co-Authors: Robert E Thomas, Catherine Overy, George H. Booth, Ali Alavi, Peter J. Knowles, Daniel OpalkaAbstract:Unbiased stochastic sampling of the one- and two-body reduced density matrices is achieved in full configuration interaction quantum Monte Carlo with the introduction of a second, “replica” ensemble of walkers, whose population evolves in imaginary time independently from the first and which entails only modest additional computational overheads. The matrices obtained from this approach are shown to be representative of full configuration-interaction quality and hence provide a realistic opportunity to achieve high-quality results for a range of properties whose operators do not necessarily commute with the Hamiltonian. A density-matrix formulated quasi-Variational Energy estimator having been already proposed and investigated, the present work extends the scope of the theory to take in studies of analytic nuclear forces, molecular dipole moments, and polarisabilities, with extensive comparison to exact results where possible. These new results confirm the suitability of the sampling technique and, where sufficiently large basis sets are available, achieve close agreement with experimental values, expanding the scope of the method to new areas of investigation.
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Unbiased reduced density matrices and electronic properties from full configuration interaction quantum Monte Carlo
The Journal of Chemical Physics, 2014Co-Authors: Catherine Overy, N. S. Blunt, Deidre Cleland, George H. Booth, James J Shepherd, Ali AlaviAbstract:Properties that are necessarily formulated within pure (symmetric) expectation values are difficult to calculate for projector quantum Monte Carlo approaches, but are critical in order to compute many of the important observable properties of electronic systems. Here, we investigate an approach for the sampling of unbiased reduced density matrices within the full configuration interaction quantum Monte Carlo dynamic, which requires only small computational overheads. This is achieved via an independent replica population of walkers in the dynamic, sampled alongside the original population. The resulting reduced density matrices are free from systematic error (beyond those present via con- straints on the dynamic itself) and can be used to compute a variety of expectation values and properties, with rapid convergence to an exact limit.Aquasi-Variational Energy estimate derived from these density matrices is proposed as an accurate alternative to the projected estimator for multiconfigurational wavefunctions, while its Variational property could potentially lend itself to accurate extrapolation approaches in larger systems.
Jean-philip Piquemal - One of the best experts on this subject based on the ideXlab platform.
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molecular dynamics using nonVariational polarizable force fields theory periodic boundary conditions implementation and application to the bond capacity model
Journal of Chemical Theory and Computation, 2019Co-Authors: Pier Paolo Poier, Louis Lagardère, Jean-philip Piquemal, Frank JensenAbstract:We extend the framework for polarizable force fields to include the case where the electrostatic multipoles are not determined by a Variational minimization of the electrostatic Energy. Such models formally require that the polarization response is calculated for all electrostatic parameters for all possible geometrical perturbations in order to obtain the Energy gradient required for performing molecular dynamics simulations. By making use of a Lagrange formalism, however, this computational demanding task can be replaced by solving a single equation similar to that for determining the polarization Energy itself. Using the recently proposed bond capacity model that describes molecular polarization at the charge-only level, we show that the Energy gradient for non-Variational Energy models with periodic boundary conditions can be calculated with a computational effort similar to that for Variational polarization models. The possibility of separating the equation for calculating the electrostatic parameters from the Energy expression depending on these parameters without a large computational penalty provides flexibility in the design of new force fields.
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Molecular Dynamics using Non-Variational Polarizable Force Fields: Theory, Periodic Boundary Conditions Implementation and Application to the Bond Capacity Model
'American Chemical Society (ACS)', 2019Co-Authors: Pier Paolo Poier, Louis Lagardère, Jean-philip Piquemal, Frank JensenAbstract:International audienceWe extend the framework for polarizable force fields to include the case where the electrostatic multipoles are not determined by a Variational minimization of the electrostatic Energy. Such models formally require that the polarization response is calculated for all electrostatic parameters for all possible geometrical perturbations in order to obtain the Energy gradient required for performing molecular dynamics simulations. By making use of a Lagrange formalism, however, this computational demanding task can be replaced by solving a single equation similar to that for determining the polarization Energy itself. Using the recently proposed bond capacity model that describes molecular polarization at the charge-only level, we show that the Energy gradient for non-Variational Energy models with periodic boundary conditions can be calculated with a computational effort similar to that for Variational polarization models. The possibility of separating the equation for calculating the electrostatic parameters from the Energy expression depending on these parameters without a large computational penalty provides flexibility in the design of new force fields
Frank Jensen - One of the best experts on this subject based on the ideXlab platform.
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molecular dynamics using nonVariational polarizable force fields theory periodic boundary conditions implementation and application to the bond capacity model
Journal of Chemical Theory and Computation, 2019Co-Authors: Pier Paolo Poier, Louis Lagardère, Jean-philip Piquemal, Frank JensenAbstract:We extend the framework for polarizable force fields to include the case where the electrostatic multipoles are not determined by a Variational minimization of the electrostatic Energy. Such models formally require that the polarization response is calculated for all electrostatic parameters for all possible geometrical perturbations in order to obtain the Energy gradient required for performing molecular dynamics simulations. By making use of a Lagrange formalism, however, this computational demanding task can be replaced by solving a single equation similar to that for determining the polarization Energy itself. Using the recently proposed bond capacity model that describes molecular polarization at the charge-only level, we show that the Energy gradient for non-Variational Energy models with periodic boundary conditions can be calculated with a computational effort similar to that for Variational polarization models. The possibility of separating the equation for calculating the electrostatic parameters from the Energy expression depending on these parameters without a large computational penalty provides flexibility in the design of new force fields.
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Molecular Dynamics using Non-Variational Polarizable Force Fields: Theory, Periodic Boundary Conditions Implementation and Application to the Bond Capacity Model
'American Chemical Society (ACS)', 2019Co-Authors: Pier Paolo Poier, Louis Lagardère, Jean-philip Piquemal, Frank JensenAbstract:International audienceWe extend the framework for polarizable force fields to include the case where the electrostatic multipoles are not determined by a Variational minimization of the electrostatic Energy. Such models formally require that the polarization response is calculated for all electrostatic parameters for all possible geometrical perturbations in order to obtain the Energy gradient required for performing molecular dynamics simulations. By making use of a Lagrange formalism, however, this computational demanding task can be replaced by solving a single equation similar to that for determining the polarization Energy itself. Using the recently proposed bond capacity model that describes molecular polarization at the charge-only level, we show that the Energy gradient for non-Variational Energy models with periodic boundary conditions can be calculated with a computational effort similar to that for Variational polarization models. The possibility of separating the equation for calculating the electrostatic parameters from the Energy expression depending on these parameters without a large computational penalty provides flexibility in the design of new force fields
Catherine Overy - One of the best experts on this subject based on the ideXlab platform.
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analytic nuclear forces and molecular properties from full configuration interaction quantum monte carlo
Journal of Chemical Physics, 2015Co-Authors: Robert E Thomas, Catherine Overy, George H. Booth, Ali Alavi, Peter J. Knowles, Daniel OpalkaAbstract:Unbiased stochastic sampling of the one- and two-body reduced density matrices is achieved in full configuration interaction quantum Monte Carlo with the introduction of a second, “replica” ensemble of walkers, whose population evolves in imaginary time independently from the first and which entails only modest additional computational overheads. The matrices obtained from this approach are shown to be representative of full configuration-interaction quality and hence provide a realistic opportunity to achieve high-quality results for a range of properties whose operators do not necessarily commute with the Hamiltonian. A density-matrix formulated quasi-Variational Energy estimator having been already proposed and investigated, the present work extends the scope of the theory to take in studies of analytic nuclear forces, molecular dipole moments, and polarisabilities, with extensive comparison to exact results where possible. These new results confirm the suitability of the sampling technique and, where sufficiently large basis sets are available, achieve close agreement with experimental values, expanding the scope of the method to new areas of investigation.
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Unbiased reduced density matrices and electronic properties from full configuration interaction quantum Monte Carlo
The Journal of Chemical Physics, 2014Co-Authors: Catherine Overy, N. S. Blunt, Deidre Cleland, George H. Booth, James J Shepherd, Ali AlaviAbstract:Properties that are necessarily formulated within pure (symmetric) expectation values are difficult to calculate for projector quantum Monte Carlo approaches, but are critical in order to compute many of the important observable properties of electronic systems. Here, we investigate an approach for the sampling of unbiased reduced density matrices within the full configuration interaction quantum Monte Carlo dynamic, which requires only small computational overheads. This is achieved via an independent replica population of walkers in the dynamic, sampled alongside the original population. The resulting reduced density matrices are free from systematic error (beyond those present via con- straints on the dynamic itself) and can be used to compute a variety of expectation values and properties, with rapid convergence to an exact limit.Aquasi-Variational Energy estimate derived from these density matrices is proposed as an accurate alternative to the projected estimator for multiconfigurational wavefunctions, while its Variational property could potentially lend itself to accurate extrapolation approaches in larger systems.
