Simplified Approach to the Mixed Time-averaging Semiclassical Initial Value Representation for the Calculation of Dense Vibrational Spectra

TL;DR

This paper introduces a simplified semiclassical method with a filter for calculating dense vibrational spectra, effectively capturing anharmonic effects without extra computational cost, and successfully applies it to iodine in krypton.

Contribution

A simplified mixed time-averaging semiclassical initial value representation method with a built-in filter for efficient vibrational spectra calculation.

Findings

Accurately reproduces experimental iodine spectral peaks.

Efficiently handles up to 108 normal modes in complex systems.

Maintains accuracy despite simplification and filtering.

Abstract

We present and test an approximate method for the semiclassical calculation of vibrational spectra. The approach is based on the mixed time-averaging semiclassical initial value representation method, which is simplified to a form that contains a filter to remove contributions from approximately harmonic environmental degrees of freedom. This filter comes at no additional numerical cost, and it has no negative effect on the accuracy of peaks from the anharmonic system of interest. The method is successfully tested for a model Hamiltonian, and then applied to the study of the frequency shift of iodine in a krypton matrix. Using a hierarchic model with up to 108 normal modes included in the calculation, we show how the dynamical interaction between iodine and krypton yields results for the lowest excited iodine peaks that reproduce experimental findings to a high degree of accuracy.