RichMol: A general variational approach for rovibrational molecular dynamics in external electric fields

TL;DR

RichMol introduces a versatile variational method for accurately simulating the rovibrational dynamics of polyatomic molecules under external electric fields, accommodating complex field configurations and molecular interactions.

Contribution

It presents a novel, fully numerical variational approach and software for modeling molecular rovibrational behavior in external electric fields, including multipole interactions up to second hyperpolarizability.

Findings

Accurate simulation of NH₃ orientation and rotational excitation.

Implementation of a flexible, efficient computational tool for external field effects.

Demonstration of effects of multiple, complex external fields on molecules.

Abstract

A general variational approach for computing the rovibrational dynamics of polyatomic molecules in the presence of external electric fields is presented. Highly accurate, full-dimensional variational calculations provide a basis of field-free rovibrational states for evaluating the rovibrational matrix elements of high-rank Cartesian tensor operators, and for solving the time-dependent Schr\"odinger equation. The effect of the external electric field is treated as a multipole moment expansion truncated at the second hyperpolarizability interaction term. Our fully numerical and computationally efficient method has been implemented in a new program, RichMol, which can simulate the effects of multiple external fields of arbitrary strength, polarization, pulse shape and duration. Illustrative calculations of two-color orientation and rotational excitation with an optical centrifuge of NH$_3$ are discussed.