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Learn about the extended configuration-interaction singles with core/valence separation (XCIS-CVS) method for modeling core-level spectroscopy in open-shell molecular systems through this 49-minute webinar presented by Avik Ojha from The Ohio State University. Discover how XCIS enhances conventional configuration-interaction singles by incorporating selected doubly substituted determinants to achieve spin-pure excited states from restricted open-shell Hartree-Fock references, effectively eliminating spin contamination issues that plague unrestricted CIS methods in open-shell systems. Explore the core/valence separation approximation that focuses the active orbital space on core orbitals relevant for core-to-valence excitations, making the method particularly valuable for studying molecules and materials with open-shell ground states and quasi-degenerate frontier molecular orbitals. Examine practical applications of XCIS-CVS to K-edge transitions in 3d transition-metal complexes, where the method demonstrates semi-quantitative agreement with experimental results for both K-edge and pre-edge orbital splittings. Gain insights into how x-ray absorption spectroscopy provides detailed information about valence virtual orbitals and understand the theoretical foundations of this variational, size-consistent wave function approach that offers improved accuracy compared to ROHF-based CIS methods. Access the implementation of these features in Q-Chem 6.4 software and learn from a researcher who has made significant contributions to electronic structure methods, excited-state theory, and computational approaches for predicting electronic and spectroscopic properties of large open-shell and transition-metal complexes.
