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Uwe Manthe - One of the best experts on this subject based on the ideXlab platform.
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full dimensional Quantum Dynamics calculations for h chd3 h2 cd3 the effect of multiple vibrational excitations
Journal of Chemical Physics, 2018Co-Authors: Roman Ellerbrock, Uwe MantheAbstract:Initial state-selected reaction probabilities for the H + CHD3 → H2 + CD3 reaction starting from various different ro-vibrational states of CHD3 are studied by accurate full-dimensional (12D) Quantum Dynamics calculation for vanishing total angular momentum (J = 0). The calculations employ the Quantum transition state concept and the multi-layer multi-configurational time-dependent Hartree approach. First results focusing on fundamental excitations and the reactivity borrowing effect were communicated recently [R. Ellerbrock and U. Manthe, J. Chem. Phys. 147, 241104 (2017)]. In the present work, all vibrational states of the methane reactant are considered. It is found that energy deposited in overtones and combination bands is less efficient in promoting reactivity than expected from separable or sudden models. Furthermore, the effects of rotational excitation on the reactivity are studied in detail.
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a multilayer multiconfigurational time dependent hartree approach for Quantum Dynamics on general potential energy surfaces
Journal of Chemical Physics, 2008Co-Authors: Uwe MantheAbstract:The multiconfigurational time-dependent Hartree (MCTDH) approach facilitates multidimensional Quantum Dynamics calculations by representing the wavepacket in an optimal set of time-dependent basis functions, called single-particle functions. Choosing these single-particle functions to be themselves multidimensional wavefunctions which are represented using a MCTDH representation, a multilayer MCTDH scheme has been constructed and used for Quantum Dynamics calculations treating up to 1000 degrees of freedom rigorously [Wang and Thoss, J. Chem. Phys. 199, 1289 (2003)]. The present work gives a practical scheme which facilitates the application of the multilayer MCTDH approach, which previously has only been employed to study systems described by model-type Hamiltonians, to molecular systems described by more complicated Hamiltonians and general potential energy surfaces. A multilayer extension of the correlation discrete variable representation (CDVR) scheme employed in MCTDH calculations studying Quantum Dynamics on general potential energy surfaces is developed and tested in a simple numerical application. The resulting multilayer MCTDH/CDVR approach might offer a perspective to rigorously describe the Quantum Dynamics of larger polyatomic systems.
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a multilayer multiconfigurational time dependent hartree approach for Quantum Dynamics on general potential energy surfaces
Journal of Chemical Physics, 2008Co-Authors: Uwe MantheAbstract:The multiconfigurational time-dependent Hartree (MCTDH) approach facilitates multidimensional Quantum Dynamics calculations by representing the wavepacket in an optimal set of time-dependent basis functions, called single-particle functions. Choosing these single-particle functions to be themselves multidimensional wavefunctions which are represented using a MCTDH representation, a multilayer MCTDH scheme has been constructed and used for Quantum Dynamics calculations treating up to 1000degrees of freedom rigorously [Wang and Thoss, J. Chem. Phys. 199, 1289 (2003)]. The present work gives a practical scheme which facilitates the application of the multilayer MCTDH approach, which previously has only been employed to study systems described by model-type Hamiltonians, to molecular systems described by more complicated Hamiltonians and general potential energy surfaces. A multilayer extension of the correlation discrete variable representation (CDVR) scheme employed in MCTDH calculations studying Quantum dy...
Scott Habershon - One of the best experts on this subject based on the ideXlab platform.
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mctdh on the fly efficient grid based Quantum Dynamics without pre computed potential energy surfaces
Journal of Chemical Physics, 2018Co-Authors: Gareth W Richings, Scott HabershonAbstract:We present significant algorithmic improvements to a recently proposed direct Quantum Dynamics method, based upon combining well established grid-based Quantum Dynamics approaches and expansions of the potential energy operator in terms of a weighted sum of Gaussian functions. Specifically, using a sum of low-dimensional Gaussian functions to represent the potential energy surface (PES), combined with a secondary fitting of the PES using singular value decomposition, we show how standard grid-based Quantum Dynamics methods can be dramatically accelerated without loss of accuracy. This is demonstrated by on-the-fly simulations (using both standard grid-based methods and multi-configuration time-dependent Hartree) of both proton transfer on the electronic ground state of salicylaldimine and the non-adiabatic Dynamics of pyrazine.
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direct Quantum Dynamics using grid based wave function propagation and machine learned potential energy surfaces
Journal of Chemical Theory and Computation, 2017Co-Authors: Gareth W Richings, Scott HabershonAbstract:We describe a method for performing nuclear Quantum Dynamics calculations using standard, grid-based algorithms, including the multiconfiguration time-dependent Hartree (MCTDH) method, where the potential energy surface (PES) is calculated “on-the-fly”. The method of Gaussian process regression (GPR) is used to construct a global representation of the PES using values of the energy at points distributed in molecular configuration space during the course of the wavepacket propagation. We demonstrate this direct Dynamics approach for both an analytical PES function describing 3-dimensional proton transfer Dynamics in malonaldehyde and for 2- and 6-dimensional Quantum Dynamics simulations of proton transfer in salicylaldimine. In the case of salicylaldimine we also perform calculations in which the PES is constructed using Hartree–Fock calculations through an interface to an ab initio electronic structure code. In all cases, the results of the Quantum Dynamics simulations are in excellent agreement with prev...
Gareth W Richings - One of the best experts on this subject based on the ideXlab platform.
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mctdh on the fly efficient grid based Quantum Dynamics without pre computed potential energy surfaces
Journal of Chemical Physics, 2018Co-Authors: Gareth W Richings, Scott HabershonAbstract:We present significant algorithmic improvements to a recently proposed direct Quantum Dynamics method, based upon combining well established grid-based Quantum Dynamics approaches and expansions of the potential energy operator in terms of a weighted sum of Gaussian functions. Specifically, using a sum of low-dimensional Gaussian functions to represent the potential energy surface (PES), combined with a secondary fitting of the PES using singular value decomposition, we show how standard grid-based Quantum Dynamics methods can be dramatically accelerated without loss of accuracy. This is demonstrated by on-the-fly simulations (using both standard grid-based methods and multi-configuration time-dependent Hartree) of both proton transfer on the electronic ground state of salicylaldimine and the non-adiabatic Dynamics of pyrazine.
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direct Quantum Dynamics using grid based wave function propagation and machine learned potential energy surfaces
Journal of Chemical Theory and Computation, 2017Co-Authors: Gareth W Richings, Scott HabershonAbstract:We describe a method for performing nuclear Quantum Dynamics calculations using standard, grid-based algorithms, including the multiconfiguration time-dependent Hartree (MCTDH) method, where the potential energy surface (PES) is calculated “on-the-fly”. The method of Gaussian process regression (GPR) is used to construct a global representation of the PES using values of the energy at points distributed in molecular configuration space during the course of the wavepacket propagation. We demonstrate this direct Dynamics approach for both an analytical PES function describing 3-dimensional proton transfer Dynamics in malonaldehyde and for 2- and 6-dimensional Quantum Dynamics simulations of proton transfer in salicylaldimine. In the case of salicylaldimine we also perform calculations in which the PES is constructed using Hartree–Fock calculations through an interface to an ab initio electronic structure code. In all cases, the results of the Quantum Dynamics simulations are in excellent agreement with prev...
Ulrich Schollwock - One of the best experts on this subject based on the ideXlab platform.
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time dependent density matrix renormalization group Quantum Dynamics for realistic chemical systems
Journal of Chemical Physics, 2019Co-Authors: Ulrich SchollwockAbstract:Electronic and/or vibronic coherence has been found by recent ultrafast spectroscopy experiments in many chemical, biological, and material systems. This indicates that there are strong and complicated interactions between electronic states and vibration modes in realistic chemical systems. Therefore, simulations of Quantum Dynamics with a large number of electronic and vibrational degrees of freedom are highly desirable. Due to the efficient compression and localized representation of Quantum states in the matrix-product state (MPS) formulation, time-evolution methods based on the MPS framework, which we summarily refer to as tDMRG (time-dependent density-matrix renormalization group) methods, are considered to be promising candidates to study the Quantum Dynamics of realistic chemical systems. In this work, we benchmark the performances of four different tDMRG methods, including global Taylor, global Krylov, and local one-site and two-site time-dependent variational principles (1TDVP and 2TDVP), with a comparison to multiconfiguration time-dependent Hartree and experimental results. Two typical chemical systems of internal conversion and singlet fission are investigated: one containing strong and high-order local and nonlocal electron-vibration couplings and the other exhibiting a continuous phonon bath. The comparison shows that the tDMRG methods (particularly, the 2TDVP method) can describe the full Quantum Dynamics in large chemical systems accurately and efficiently. Several key parameters in the tDMRG calculation including the truncation error threshold, time interval, and ordering of local sites were also investigated to strike the balance between efficiency and accuracy of results.Electronic and/or vibronic coherence has been found by recent ultrafast spectroscopy experiments in many chemical, biological, and material systems. This indicates that there are strong and complicated interactions between electronic states and vibration modes in realistic chemical systems. Therefore, simulations of Quantum Dynamics with a large number of electronic and vibrational degrees of freedom are highly desirable. Due to the efficient compression and localized representation of Quantum states in the matrix-product state (MPS) formulation, time-evolution methods based on the MPS framework, which we summarily refer to as tDMRG (time-dependent density-matrix renormalization group) methods, are considered to be promising candidates to study the Quantum Dynamics of realistic chemical systems. In this work, we benchmark the performances of four different tDMRG methods, including global Taylor, global Krylov, and local one-site and two-site time-dependent variational principles (1TDVP and 2TDVP), with a ...
Habershon Scott - One of the best experts on this subject based on the ideXlab platform.
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Data for A new diabatization scheme for direct Quantum Dynamics : Procrustes diabatization
'AIP Publishing', 2020Co-Authors: Richings Gareth, Habershon ScottAbstract:We present a new scheme for diabatizing electronic potential energy surfaces, for use within the recently implemented direct-Dynamics grid-based (DD-GB) class of computational nuclear Quantum Dynamics methods (DD-SM and DD-MCTDH), called Procrustes diabatization. Calculations on the well-studied molecular systems LiF and the butatriene cation, using both Procrustes diabatization and the previously implemented propagation and projection diabatization schemes, have allowed detailed comparisons to be made which indicate that the new method combines the best features of the older approaches; it generates smooth surfaces which cross at the correct molecular geometries, reproduces interstate couplings accurately and hence allows the correct modelling of non-adiabatic Dynamics
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A new diabatization scheme for direct Quantum Dynamics : procrustes diabatization
'AIP Publishing', 2020Co-Authors: Richings Gareth, Habershon ScottAbstract:We present a new scheme for diabatizing electronic potential energy surfaces, for use within the recently implemented direct-Dynamics grid-based (DD-GB) class of computational nuclear Quantum Dynamics methods (DD-SM and DD-MCTDH), called Procrustes diabatization. Calculations on the well-studied molecular systems LiF and the butatriene cation, using both Procrustes diabatization and the previously implemented propagation and projection diabatization schemes, have allowed detailed comparisons to be made which indicate that the new method combines the best features of the older approaches; it generates smooth surfaces which cross at the correct molecular geometries, reproduces interstate couplings accurately and hence allows the correct modelling of non-adiabatic Dynamics
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Direct grid-based Quantum Dynamics on propagated diabatic potential energy surfaces
'Elsevier BV', 2017Co-Authors: Habershon Scott, Richings GarethAbstract:We present a method for performing non-adiabatic, grid-based nuclear Quantum Dynamics calculations using diabatic potential energy surfaces (PESs) generated “on-the-fly”. Gaussian process regression is used to interpolate PESs by using electronic structure energies, calculated at points in configuration space determined by the nuclear Dynamics, and diabatising the results using the propagation diabatisation method reported recently (Richings and Worth, 2015). Our new method is successfully demonstrated using a grid-based approach to model the non-adiabatic Dynamics of the butatriene cation. Overall, our scheme offers a route towards accurate Quantum Dynamics on diabatic PESs learnt on-the-fly
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Data for Direct grid-based Quantum Dynamics on propagated diabatic potential energy surfaces
Department of Chemistry University of Warwick, 2017Co-Authors: Habershon Scott, Richings GarethAbstract:We present a method for performing non-adiabatic, grid-based nuclear Quantum Dynamics calculations using diabatic potential energy surfaces (PESs) generated “on-the-fly”. Gaussian process regression is used to interpolate PESs by using electronic structure energies, calculated at points in configuration space determined by the nuclear Dynamics, and diabatising the results using the propagation diabatisation method reported recently (Richings and Worth, 2015). Our new method is successfully demonstrated using a grid-based approach to model the non-adiabatic Dynamics of the butatriene cation. Overall, our scheme offers a route towards accurate Quantum Dynamics on diabatic PESs learnt on-the-fly
