Using a proxy state to improve the accuracy of truncated hyperpolarizability calculations

TL;DR

This paper introduces a proxy state method that improves the accuracy of truncated hyperpolarizability calculations by incorporating sum rules and off-resonant polarizability, enhancing predictions of nonlinear optical properties.

Contribution

The paper presents a novel proxy state algorithm that accounts for state truncation in hyperpolarizability calculations, improving accuracy over traditional methods.

Findings

Benchmarking shows improved accuracy with the proxy state method.

The method effectively incorporates sum rules and off-resonant polarizability.

Enhanced predictions of nonlinear optical properties are demonstrated.

Abstract

We have developed a simple algorithm for defining a single proxy state which accounts for state truncation in the sum-over-states calculations of the dispersion of the molecular hyperpolarizabilities. The transition strengths between the proxy state and the truncated set of states are determined using the Thomas-Reiche-Kuhn sum rules. In addition to the sum rules, this method requires as an input the off-resonant polarizability. This proxy state method can augment experimentally determined parameters or finite-state theories to allow for a more accurate prediction of the nonlinear optical properties of molecular systems. We benchmark this approach by comparison with exact perturbation calculations of one-dimensional power law potentials.