Structural Relaxation of Materials with Spin-Orbit Coupling: Analytical Forces in Spin-Current DFT

TL;DR

This paper develops analytical gradients for spin-current density functional theory including spin-orbit coupling, showing significant structural effects in iodine crystals and emphasizing the need for SCDFT with explicit spin-current dependence.

Contribution

It introduces analytical force calculations in spin-current DFT with SOC, enabling accurate structural predictions and highlighting the importance of spin-current effects.

Findings

SOC can modify crystal structures by over 50% in iodine crystals.

Analytical gradients are feasible within a two-component SCDFT framework.

Implementation in the Crystal program facilitates practical applications.

Abstract

Analytical gradients of the total energy are provided for local density and generalized-gradient hybrid approximations to generalized Kohn-Sham spin-current density functional theory (SCDFT). It is shown that gradients may be determined analytically, in a two-component framework, including spin-orbit coupling (SOC), with high accuracy. We demonstrate that renormalization of the electron-electron potential by SOC-induced spin-currents can account for considerable modification of crystal structures. In the case of Iodine-based molecular crystals, the effect may amount to more than half of the total modification of the structure by SOC. Such effects necessitate an SCDFT, rather than DFT, formulation, in which exchange-correlation functionals are endowed with an explicit dependence on spin-current densities. An implementation is presented in the \textsc{Crystal} program.