State-specific Variational Quantum Monte Carlo for Point Defect Excited States*

In recent years, much progress has been made in electronic structure calculations of spin defects from first principles, for example using quantum embedding theories [1,2]. However, several important controversies remain open in comparing different theoretical approaches and their respective results with experiments. Hence, the development of methods to obtain systematically improvable reference excitation energies of defects is a key priority. Quantum Monte Carlo techniques, particularly state-specific Variational Monte Carlo, have recently seen significant progress in the quality of the wave function ansatzes and optimization algorithms that can be employed for the description of excited states and have provided reliable excitation energies in molecular settings [3]. In this work, we extend the use of state-specific Variational Monte Carlo to the investigation of excited states of point defects in solids with the QMCPACK code and present preliminary results characterizing its accuracy, with the vacancy defect in diamond as an initial test case.

[1] C. Vorwerk et al. Nat. Comput. Sci. 2, 424 (2022).

[2] A. Mitra et al. J. Phys. Chem Lett. 12, 11688 (2021).

[3] L. Otis, I. Craig, and E. Neuscamman. J. Chem. Phys. 153, 234105 (2020).