Novel Approach to Structural Relaxation of Materials in Optically Excited States

TL;DR

This paper introduces a first-principles method based on the Bethe-Salpeter equation for efficiently relaxing the geometry of materials in optically excited states, capturing exciton and atomic displacement details.

Contribution

It presents a novel, single-iteration approach to relax excited-state geometries using coupled exciton and atomic displacement equations.

Findings

Successfully applied to CO, H₂O, and NH₃ molecules.

Provides insights into the relaxation mechanisms via phonon modes.

Achieves energy and wavefunction characterization of self-trapped excitons.

Abstract

We present a first-principles method for relaxing a material's geometry in an optically excited state. This method, based on the Bethe-Salpeter equation, consists of solving coupled equations for exciton wavefunctions and atomic displacements. Our approach allows for structural relaxation of excited states to be achieved through a single iteration. As results, one obtains not only energy and wavefunction of the thus modified, i.e. self-trapped, exciton, but also the mechanism of relaxation in terms of atomic displacements in the respective phonon eigenmodes. We demonstrate and evaluate our formalism with the example of the three molecules CO, H$_{2}$O, and NH$_{3}$.