Quasi-relativistic approach to analytical gradients of parity violating potentials

TL;DR

This paper develops an analytic gradient method within a quasirelativistic framework to compute parity-violating potential derivatives in chiral molecules, enabling accurate estimation of PV frequency splittings and anharmonic effects.

Contribution

It introduces a new analytic gradient approach for PV potentials in a quasirelativistic mean-field framework, allowing detailed vibrational analysis including multi-mode effects.

Findings

PV frequency shifts agree with previous theoretical values.

Multi-mode effects significantly influence vibrational frequency shifts.

The method efficiently estimates anharmonic contributions in chiral molecules.

Abstract

An analytic gradient approach for the computation of derivatives of parity-violating (PV) potentials with respect to displacements of the nuclei in chiral molecules is described and implemented within a quasirelativistic mean-field framework. Calculated PV potential gradients are utilised for estimating PV frequency splittings between enantiomers in rotational and vibrational spectra of four chiral polyhalomethanes, i.e. CHBrClF, CHClFI, CHBrFI and CHAtFI. Values calculated within the single-mode approximation for the frequency shifts agree well with previously reported theoretical values. The influence of non-separable anharmonic effects (multi-mode effects) on the vibrational frequency shifts, which are readily accessible with the present analytic derivative approach, are estimated for the C--F stretching fundamental of all four molecules and computed for each of the fundamentals in CHBrClF and CHAtFI. Multi-mode effects are found to be significant, in particular for the C--F stretching modes, being for some modes and cases of similar size as the single-mode contribution.