EOM-CC guide to Fock-space travel: The C2 edition

S. Gulania, T.-C. Jagau, and A. I. Krylov
Faraday Disc.  217, 514 – 532 (2019)

Despite their small size, C2 species pose a big challenge to electronic structure owing to extensive electronic degeneracies and multi-configurational wave functions leading to a dense manifold of electronic states. We present detailed electronic structure calculations of C2, C2-, and C22- emphasizing spectroscopically relevant properties. We employ double ionization potential (DIP) and ionization potential (IP) variants of equation-of-motion coupled-cluster method with single and double substitutions (EOM-CCSD) and a dianionic reference state. We show that EOM-CCSD is capable of describing multiple interacting states in C2 and C2- in an accurate, robust, and effective way. We also characterize the electronic structure of C22-, which is metastable with respect to electron detachment.

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