Optical Susceptibilities of Polymers: Current-Current versus Dipole-Dipole Correlation

TL;DR

This paper compares current-current and dipole-dipole correlation methods for calculating nonlinear optical susceptibilities in polymers, demonstrating the superiority of dipole-dipole correlation through analytical results and model analysis.

Contribution

It introduces a well-defined dipole-dipole correlation approach that resolves issues with current-current correlation in nonlinear optical susceptibility calculations.

Findings

Dipole-dipole correlation yields physically meaningful susceptibilities.

Analytical results for SSH and TLM models are provided.

Previous methods led to unphysical divergences.

Abstract

The static current operator leads to definitional zero frequency divergence and unphysical results in studying nonlinear optical susceptibilities of polymers. A well-defined dipole-dipole correlation is superior to the complicated current-current correlation to solve this problem. As illustrative examples, optical susceptibilities under both SSH and TLM models of trans-(CH)_x are studied. New analytical results are obtained. The reasons of previous improper results are analyzed.