Stochastic Multi Configuration Time-Dependent Hartree for Dissipative Quantum Dynamics with Strong Intramolecular Coupling

TL;DR

This paper advances the stochastic Multi-Configuration Time-Dependent Hartree method to accurately simulate dissipative quantum dynamics in strongly coupled multidimensional systems, incorporating new Lindblad operators for improved thermalization.

Contribution

It introduces novel Lindblad dissipative operators and a normal mode transformation to handle strong intramolecular coupling within the stochastic MCTDH framework.

Findings

Method achieves thermalization in strongly coupled systems.

Normal mode transformation reduces intermode coupling effects.

Effective in modeling Fermi resonances and anharmonicity.

Abstract

In this article, we explore the dissipation dynamics of a strongly coupled multidimensional system in contact with a Markovian bath following a system-bath approach. We use in this endeavour the recently developed stochastic Multi-Configuration Time-Dependent Hartree approach within the Monte Carlo wave packet formalism [J.Chem.Phys.156, 094109 (2022)]. The method proved to yield thermalized ensembles of wave packets when intramolecular coupling is weak. To treat strongly coupled systems, new Lindblad dissipative operators are constructed as linear combinations of the system coordinates and associated momenta. These are obtained by an unitary transformation to a normal mode representation, which reduces intermode coupling up to second order. Additionally, we use combinations of generalized raising/lowering operators to enforce the Boltzmann distribution in the dissipation operators, which yield perfect thermalization in the harmonic limit. The two ansatz are tested using a model two-dimensional hamiltonian parameterized to disentangle the effects of intramolecular potential coupling, of strong mode mixing observed in Fermi resonances, and of anharmonicity.