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Communication: Multi-reference Approach to the Computation of Double-Core-Hole Spectra

Abstract

Double-Core Hole (DCH) states of small molecules are assessed with the restricted<br />active space self-consistent field (RASSCF) and multi-state restricted active space perturbation<br />theory of second order (MS-RASPT2) approximations. To ensure an unbiased<br />description of the relaxation and correlation effects on the DCH states, the neutral<br />ground state and DCH wave functions are optimized separately, whereas the spectral<br />intensities are computed with a biorthonormalized set of molecular orbitals within the<br />state-interaction (SI) approximation. Accurate shake-up satellites binding energies and<br />intensities of double-core-ionized states (K<sup>-2</sup>) are obtained for H<sub>2</sub>O, N<sub>2</sub>, CO and C<sub>2</sub>H<sub>2n</sub><br />(n=1–3). The results are analyzed in detail and show excellent
agreement with recent theoretical and experimental data. The K^{-2} shake-up spectra
of H2O and the C2H2n molecules are here completely characterized for the first time.

Version notes

Cholesky localization used throughout

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