Optical excitations of α–RuCl₃ using real-space quantum Monte Carlo

α–RuCl₃ has been an intensely studied material in recent years due to its exotic electronic and magnetic properties. It is a quasi-2D system with an insulating ground state which exhibits a few energetically close magnetic states and conjectured to realize Kitaev's spin-liquid. It has been suggested that the inclusion of spin-orbit coupling effects of the Ru atom and an accurate description of electron correlations is critical for the proper description of the electronic and magnetic properties of α–RuCl₃. We study the ferromagnetic and non-magnetic phases of this material with a highly accurate diffusion Monte Carlo (DMC) method to investigate these aspects. In particular, we aim to calculate the optical gaps using spin-orbit averaged potentials with fixed-node DMC, as well as using explicit spin-orbit potentials with fixed-phase DMC and 2-component formalism. Our goal is to shed light on the significance of spin-orbit effects and electron correlations on the key quantities such as band excitations and cohesive energy.