Forces and atomic relaxations in the pSIC approach with ultrasoft pseudopotentials

TL;DR

This paper introduces an efficient scheme for calculating forces within the pSIC framework using ultrasoft pseudopotentials, implemented in Quantum ESPRESSO, and demonstrates improved geometric predictions over standard DFT in systems affected by self-interaction errors.

Contribution

The authors develop and implement a force calculation scheme for pSIC with ultrasoft pseudopotentials in plane-wave DFT codes, enabling more accurate geometry predictions for correlated materials.

Findings

pSIC predicts geometries closer to experiments where self-interaction errors are significant

The scheme is validated with tests on ZnO and CeO2 crystals

Applications to perovskites and silicon demonstrate its effectiveness

Abstract

We present the scheme that allows for efficient calculations of forces in the framework of pseudopotential self-interaction corrected (pSIC) formulation of the density functional theory. The scheme works with norm conserving and also with ultrasoft pseudopotentials and has been implemented in the plane-wave basis code {\sc quantum espresso}. We have performed tests of the internal consistency of the derived expressions for forces considering ZnO and CeO$_2$ crystals. Further, we have performed calculations of equilibrium geometry for LaTiO$_3$, YTiO$_3$, and LaMnO$_3$ perovskites and also for Re and Mn pairs in silicon. Comparison with standard DFT and DFT+U approaches shows that in the cases where spurious self-interaction matters, the pSIC approach predicts different geometry, very often closer to the experimental data.