Spin-orbit Hamiltonian for organic crystals from first principles electronic structure and Wannier functions

TL;DR

This paper introduces a first-principles method combining density functional theory and Wannier functions to construct effective spin-orbit Hamiltonians for organic crystals, simplifying calculations of spin-related phenomena.

Contribution

The method allows direct evaluation of spin-orbit Hamiltonians over Wannier functions without needing to compute spin-orbit-split bands, addressing a key computational challenge.

Findings

Successfully applied to molecules, atomic chains, and organic crystals.

Eliminates the need for spin-orbit band disentanglement.

Provides a practical tool for spin dynamics studies in organic materials.

Abstract

Spin-orbit coupling in organic crystals is responsible for many spin-relaxation phenomena, going from spin diffusion to intersystem crossing. With the goal of constructing effective spin-orbit Hamiltonians to be used in multiscale approaches to the thermodynamical properties of organic crystals, we present a method that combines density functional theory with the construction of Wannier functions. In particular we show that the spin-orbit Hamiltonian constructed over maximally localised Wannier functions can be computed by direct evaluation of the spin-orbit matrix elements over the Wannier functions constructed in absence of spin-orbit interaction. This eliminates the prob- lem of computing the Wannier functions for almost degenerate bands, a problem always present with the spin-orbit-split bands of organic crystals. Examples of the method are presented for isolated molecules, for mono-dimensional chains of Pb and C atoms and for triarylamine-based one-dimansional single crystals.