Journal Article multiconfigurational wavefunction CASPT2 Macrocyclic Compounds Organometallic Compounds Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. Thymidine VC2W18DGKR X-ray absorption spectroscopy X-ray spectroscopy charge transfer computational cost configuration interaction electron correlation excited states gradients high performance computing molecular dynamics multiconfigurational perturbation theory parallelization parallellization relativistic spin-orbit coupling transition metals