Multielectron effects in high harmonic generation in N2 and benzene: simulation using a non-adiabatic quantum molecular dynamics approach for laser-molecule interactions

TL;DR

This paper introduces a mixed quantum-classical simulation approach using TDDFT to model high harmonic generation in molecules like N2 and benzene under intense laser pulses, revealing polarization-dependent effects.

Contribution

It presents a novel non-adiabatic quantum molecular dynamics method combining TDDFT with grid-based numerical solutions for laser-molecule interactions, applied to high harmonic generation in benzene and N2.

Findings

Enhanced high harmonics when laser is perpendicular to N2 axis.

Suppressed high harmonics when laser is parallel to benzene plane.

First TDDFT calculations of HHG in benzene with linearly polarized pulses.

Abstract

A mixed quantum-classical approach is introduced which allows the dynamical response of molecules driven far from equilibrium to be modeled. This method is applied to the interaction of molecules with intense, short-duration laser pulses. The electronic response of the molecule is described using time-dependent density functional theory (TDDFT) and the resulting Kohn-Sham equations are solved numerically using finite difference techniques in conjunction with local and global adaptations of an underlying grid in curvilinear coordinates. Using this approach, simulations can be carried out for a wide range of molecules and both all-electron and pseudopotential calculations are possible. The approach is applied to the study of high harmonic generation in N2 and benzene using linearly-polarized laser pulses and, to the best of our knowledge, the results for benzene represent the first TDDFT calculations of high harmonic generation in benzene using linearly polarized laser pulses. For N2 an enhancement of the cut-off harmonics is observed whenever the laser polarization is aligned perpendicular to the molecular axis. This enhancement is attributed to the symmetry properties of the Kohn-Sham orbital that responds predominantly to the pulse. In benzene we predict that a suppression in the cut-off harmonics occurs whenever the laser polarization is aligned parallel to the molecular plane. We attribute this suppression to the symmetry-induced response of the highest-occupied molecular orbital.