RPA methods for X-ray spectroscopy

X-ray spectroscopies such as XPS, XES and XAS provide local information of charge accommodation as they probe core-electrons and their transitions. XPS methods are now being used in conjunction with liquids, where the nature of chemical shifts, i.e. change in core-electron binding energies (CEBEs) upon solvation, is poorly understood. Simulating theoretical XPS is challenging due to high lying nature of core excitations, large relaxation effects, and relativistic effects. We have recently shown that the generalized Kohn–Sham random phase approximation (GKS-RPA) method provides effective one-particle energies which can be used to estimate the CEBEs. In addition, the GKS-RPA Hamiltonian can be partitioned into static, relaxation and correlation effects which provides valuable physical insights into the nature chemical shifts.

We are now extending GKS-RPA methods with analytic continuation and MPI coding to enable fast computation of IPs. We are also working on incorporating relativistic effects, which are necessary for the study of transition metal complexes.