Improved algorithm for the direct dynamics variational multi-configurational Gaussian method

Christopoulou, Georgia; Freibert, Antonia; Worth, Graham A.

doi:10.1063/5.0043720

Cited by 19 publications

(18 citation statements)

References 51 publications

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“…DD-vMCG is a frozen Gaussian nuclear dynamics method that shares the wavefunction ansatz with the full multiple spawning method of Curchod and Martínez [ 37 , 46 ] and the coupled coherent method of Shalashilin [ 47 ], but both these methods use classical trajectories to propagate the Gaussian centres, while in vMCG the Gaussian basis functions follow variationally determined trajectories to keep the basis set optimally small. The method has been describe extensively in the literature [ 48 , 49 , 50 ] and will only be outlined here.…”

Section: Methodsmentioning

confidence: 99%

“…The DD-vMCG method takes advantage of previously calculated electronic structure points stored in a database to construct the full potential energy surfaces [ 50 ]. Initially, a calculation including energies, gradients, nonadiabatic couplings and Hessians at the Frank-Condon point is carried out with the electronic structure method of choice.…”

Section: Methodsmentioning

confidence: 99%

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Micro-Solvated DMABN: Excited State Quantum Dynamics and Dual Fluorescence Spectra

2021

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In this work, we report a complete analysis by theoretical and spectroscopic methods of the short-time behaviour of 4-(dimethylamino)benzonitrile (DMABN) in the gas phase as well as in cyclohexane, tetrahydrofuran, acetonitrile, and water solution, after excitation to the La state. The spectroscopic properties of DMABN were investigated experimentally using UV absorption and fluorescence emission spectroscopy. The computational study was developed at different electronic structure levels and using the Polarisable Continuum Model (PCM) and explicit solvent molecules to reproduce the solvent environment. Additionally, excited state quantum dynamics simulations in the diabatic picture using the direct dynamics variational multiconfigurational Gaussian (DD-vMCG) method were performed, the largest quantum dynamics “on-the-fly” simulations performed with this method until now. The comparison with fully converged multilayer multiconfigurational time-dependent Hartree (ML-MCTDH) dynamics on parametrised linear vibronic coupling (LVC) potentials show very similar population decays and evolution of the nuclear wavepacket. The ring C=C stretching and three methyl tilting modes are identified as the responsible motions for the internal conversion from the La to the Lb states. No major differences are observed in the ultrafast initial decay in different solvents, but we show that this effect depends strongly on the level of electronic structure used.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Micro-Solvated DMABN: Excited State Quantum Dynamics and Dual Fluorescence Spectra

2021

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“…Full details of how the QC database is generated are given in refs. [6,46]. In brief, points are added to the database when the centre of a GWP (or point on a trajectory) is further than a specified distance from any point in the database.…”

Section: Methodsmentioning

confidence: 99%

“…The QC data are transformed to the diabatic picture using a global diabatisation scheme [13], in which the adiabatic-diabatic transformation matrix is propagated using the calculated derivative couplings. This scheme has been shown to provide globally consistent surfaces for a two-state system [46]. The QC database can also be either generated or used by either DD-TSH or DD-vMCG calculations.…”

Section: Methodsmentioning

confidence: 99%

Mixed-quantum-classical or fully-quantized dynamics? A unified code to compare methods

Coonjobeeharry

Spinlove

Sanz-Sanz

et al. 2022

Phil. Trans. R. Soc. A.

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Three methods for non-adiabatic dynamics are compared to highlight their capabilities. Multi-configurational time-dependent Hartree is a full grid-based solution to the time-dependent Schrödinger equation, variational multi-configurational Gaussian (vMCG) uses a less flexible but unrestricted Gaussian wavepacket basis, and trajectory surface hopping (TSH) replaces the nuclear wavepacket with a swarm of classical trajectories. Calculations with all methods using a model Hamiltonian were performed. The vMCG and TSH were also then run in a direct dynamics mode, with the potential energy surfaces calculated on-the-fly using quantum chemistry calculations. All dynamics calculations used the Q uantics package, with the TSH calculations using a new interface to a surface hopping code. A novel approach to calculate adiabatic populations from grid-based quantum dynamics using a time-dependent discrete variable representation is presented, allowing a proper comparison of methods. This article is part of the theme issue ‘Chemistry without the Born–Oppenheimer approximation’.

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“…The theory is sophisticated in that it address the two-(or more-) layer Gaussian multiconfiguration time-dependent Hartree method [13] in the context of on-the-fly scheme, which are expected to have a vast application realm of large molecular systems of many vibronic modes. Worth and his group have developed the improved direct dynamics variational multi-configurational Gaussian method for nonadiabatic dynamics [47].…”

Section: Nonadiabatic Quantum Dynamicsmentioning

confidence: 99%

Time-dependent variational dynamics for nonadiabatically coupled nuclear and electronic quantum wavepackets in molecules

Takatsuka

2021

Eur. Phys. J. D

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We propose a methodology to unify electronic and nuclear quantum wavepacket dynamics in molecular processes including nonadiabatic chemical reactions. The canonical and traditional approach in the full quantum treatment both for electrons and nuclei rests on the Born–Oppenheimer fixed nuclei strategy, the total wavefunction of which is described in terms of the Born–Huang expansion. This approach is already realized numerically but only for small molecules with several number of coupled electronic states for extremely hard technical reasons. Besides, the stationary-state view of the relevant electronic states based on the Born–Oppenheimer approximation is not always realistic in tracking real-time electron dynamics in attosecond scale. We therefore incorporate nuclear wavepacket dynamics into the scheme of nonadiabatic electron wavepacket theory, which we have been studying for a long time. In this scheme thus far, electron wavepackets are quantum mechanically propagated in time along nuclear paths that can naturally bifurcate due to nonadiabatic interactions. The nuclear paths are in turn generated simultaneously by the so-called matrix force given by the electronic states involved, the off-diagonal elements of which represent the force arising from nonadiabatic interactions. Here we advance so that the nuclear wavepackets are directly taken into account in place of path (trajectory) approximation. The nuclear wavefunctions are represented in terms of the Cartesian Gaussians multiplied by plane waves, which allows for feasible calculations of atomic and molecular integrals together with the electronic counterparts in a unified manner. The Schrödinger dynamics of the simultaneous electronic and nuclear wavepackets are to be integrated by means of the dual least action principle of quantum mechanics [K. Takatsuka, J. Phys. Commun. 4, 035007 (2020)], which is a time-dependent variational principle. Great contributions of Vincent McKoy in the electron dynamics in the fixed nuclei approximation and development in time-resolved photoelectron spectroscopy are briefly outlined as a guide to the present work.

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Improved algorithm for the direct dynamics variational multi-configurational Gaussian method

Cited by 19 publications

References 51 publications

Micro-Solvated DMABN: Excited State Quantum Dynamics and Dual Fluorescence Spectra

Micro-Solvated DMABN: Excited State Quantum Dynamics and Dual Fluorescence Spectra

Mixed-quantum-classical or fully-quantized dynamics? A unified code to compare methods

Time-dependent variational dynamics for nonadiabatically coupled nuclear and electronic quantum wavepackets in molecules

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