Modeling Non-Reversible Molecular Internal Conversion Using the Time-dependent Variational Approach with sD2 Ansatz

TL;DR

This paper investigates how non-linear system-bath interactions affect molecular internal conversion dynamics, using a variational approach that captures entangled states and bath wavepacket effects, revealing non-reversible processes and computational efficiencies.

Contribution

It introduces a variational method with the sD2 ansatz to model non-reversible internal conversion driven by quadratic system-bath coupling, accounting for non-Gaussian bath wavepackets.

Findings

Quadratic coupling induces non-reversible internal conversion.

Bath wavepackets become broadened and asymmetrically squeezed.

Using degenerate coherent states reduces computational effort.

Abstract

Effects of non-linear coupling between the system and the bath vibrational modes on the system internal conversion dynamics are investigated using the Dirac-Frenkel variational approach with the defined sD2 ansatz. It explicitly accounts for the entangled system electron-vibrational wavepacket states, while the bath quantum harmonic oscillator (QHO) states are expanded in a superposition of coherent states (CS). Using a non-adiabatically coupled three-level model, we show that quadratic system-bath coupling induces non-reversible internal conversion when the bath QHO wavepacket representation is highly non-Gaussian. The quadratic coupling results in a broadened and asymmetrically squeezed bath QHO wavepackets in the coordinate-momentum phase space. Additionally, we found that computational effort can be reduced using degenerate CSs to represent the initial bath wavepackets.