Magnetization dynamics with time-dependent spin-density functional theory: significance of exchange-correlation torques

TL;DR

This paper explores the role of exchange-correlation magnetic fields in spin-density-functional theory, demonstrating their importance in accurately modeling magnetization dynamics, especially near phase transitions, through comparisons with exact solutions.

Contribution

It highlights the significance of exchange-correlation torques in noncollinear SDFT and assesses their impact on magnetization dynamics using orbital-dependent approximations.

Findings

Exchange-correlation torques influence magnetization dynamics.

Exchange-only approximations work well for weak to moderate interactions.

Both exchange and correlation torques are important near phase transitions.

Abstract

In spin-density-functional theory (SDFT) for noncollinear magnetic materials, the Kohn-Sham system features exchange-correlation (xc) scalar potentials and magnetic fields. The significance of the xc magnetic fields is not very well explored; in particular, they can give rise to local torques on the magnetization, which are absent in standard local and semilocal approximations. Exact benchmark solutions for a five-site extended Hubbard lattice at half filling and in the presence of spin-orbit coupling are compared with SDFT results obtained using orbital-dependent exchange-only approximations. The magnetization dynamics following short-pulse excitations is found to be reasonably well described in the exchange-only approximation for weak to moderate interactions. For stronger interactions and near transitions between magnetically ordered and frustrated phases, exchange and correlation torques tend to compensate each other and must both be accounted for.