Variational vibrational states of HCOOH

TL;DR

This paper computes the vibrational states of formic acid using an advanced quantum approach, incorporating torsional and normal coordinates, and reports states up to and beyond the isomerization barrier.

Contribution

It introduces a variational method combining the GENIUSH-Smolyak approach with a detailed coordinate system for accurate vibrational state calculations of HCOOH.

Findings

Vibrational states up to the isomerization barrier are identified.

The method successfully describes trans, cis, and delocalized states.

The approach provides detailed insights into the vibrational structure of formic acid.

Abstract

Vibrational states of the formic acid molecule are converged using the GENIUSH-Smolyak approach and the potential energy surface taken from [D. Tew and W. Mizukami, J. Phys. Chem. A 120, 9815 (2016)]. The quantum nuclear motion is described by using the $cis$-$trans$ torsional coordinate and eight curvilinear normal coordinates defined with respect to an instantaneous reference configuration changing as a function of the torsional degree of freedom. Harmonic oscillator basis functions are used for the curvilinear normal coordinates, a Fourier basis for the torsional coordinate, and a simple basis pruning condition is combined with a Smolyak integration grid. $Trans$, $cis$, and $delocalized$ vibrational states are reported up to and slightly beyond the isomerization barrier.