Multi-Reference Linear Response Methods for Core Electron Spectroscopy
In one of our recent articles, we show how to adapt the CASSCF-LR method for simulating K-edges of X-ray absorption spectra. The high-energy core-to-valence transitions can be reached either by a core-valence separation approximation or by a special algorithm for finding interior eigenvalues of the LR eigenvalue equations. First results for K-edges are encouraging. Of all available MR methods only the CASSCF-LR approach was able to describe the correct peak order for O-K-edges of MnO4- and ozone. As for the simulation of valence electronic spectra, including dynamic correlation will significantly increase the accuracy and will help us to gain new insights on the electronic structure of transition-metal containing molecules.
B. Helmich-Paris; Simulating X-ray absorption spectra with complete active space self-consistent field linear response methods, Int J Quantum Chem. 2020 e26559. https://doi.org/10.1002/qua.26559