Symmetry-consistent expansion of interaction kernels between rigid molecules

TL;DR

This paper develops a symmetry-consistent expansion method for interaction kernels between anisotropic rigid molecules, enabling derivation of macroscopic models while respecting molecular and cluster symmetries.

Contribution

It introduces a systematic expansion of interaction kernels using symmetric traceless tensors that incorporates both cluster and molecular symmetries, including point group considerations.

Findings

Expansion expressed by symmetric traceless tensors with identified independent terms

Decomposition of tensors into subspaces based on improper rotations

Method applicable to various molecular point groups

Abstract

We discuss the expansion of interaction kernels between anisotropic rigid molecules. The expansion decouples the correlated orientational variables so that it can be utilized to derive macroscopic models. Symmetries of two types are considered. First, we examine the symmetry of the interacting cluster, including the translation and rotation of the whole cluster, and label permutation within the cluster. The expansion is expressed by symmetric traceless tensors, and the linearly independent terms are identified. Then, we study the molecular symmetry characterized by a point group in $O(3)$. The proper rotations determine what symmetric traceless tensors can appear. The improper rotations decompose these tensors into two subspaces and determine how the tensors in the two subspaces are coupled. For each point group, we identify the two subspaces, so that the expansion consistent with the point group is established.