Equation-of-motion coupled-cluster theory to model L-edge x-ray absorption and photoelectron spectra

M. L. Vidal, P. Pokhilko, A.I. Krylov, and S. Coriani
J. Phys. Chem. Lett.  11, 8314 – 8321 (2020)

We present an extension of the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) theory for computing x-ray L-edge spectra, both in the absorption (XAS) and photoelectron (XPS) regimes. The approach is based on the perturbative evaluation of spin-orbit couplings using the Breit-Pauli Hamiltonian and non- relativistic wave-functions described by the fc-CVS-EOM-CCSD ansatz (EOM-CCSD within the frozen-core core-valence separated (fc-CVS) scheme). The formalism is based on spinless one-particle density matrices. The approach is illustrated by modeling XAS and XPS of several model systems ranging from argon atoms to small molecules containing sulfur and silicon.

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