The Moving-Grid Effect in the Harmonic Vibrational Frequency Calculations with Numeric Atom-Centered Orbitals

TL;DR

This paper investigates how the moving-grid effect influences harmonic vibrational frequency calculations using numeric atom-centered orbitals, revealing its significant impact on second derivatives and proposing efficient mitigation strategies.

Contribution

The study identifies the importance of the moving-grid effect on vibrational frequencies and introduces methods to mitigate its impact in both molecular and periodic systems.

Findings

Moving-grid effect significantly affects vibrational frequency calculations.

Diagonal force constants are mainly impacted by the moving-grid effect.

Translational symmetry can be used to bypass the effect efficiently.

Abstract

When using atom-centered integration grids, the portion of the grid that belongs to a certain atom also moves when this atom is displaced. In the paper, we investigate the moving-grid effect in the calculation of the harmonic vibrational frequencies when using all-electron full-potential numeric atomic-centered orbitals as the basis set. We find that, unlike the first order derivative (i.e., forces), the moving-grid effect plays an essential role for the second order derivatives (i.e., vibrational frequencies). Further analysis reveals that predominantly diagonal force constant terms are affected, which can be bypassed efficiently by invoking translational symmetry. Our approaches have been demonstrated in both finite (molecules) and extended (periodic) systems.