TY  - JOUR
A1  - Ehlert, Christopher
A1  - Klamroth, Tillmann
T1  - The quest for best suited references for configuration interaction singles calculations of core excited states
JF  - Journal of computational chemistry : organic, inorganic, physical, biological
N2  - Near edge X-ray absorption fine structure (NEXAFS) simulations based on the conventional configuration interaction singles (CIS) lead to excitation energies, which are systematically blue shifted. Using a (restricted) open shell core hole reference instead of the Hartree Fock (HF) ground state orbitals improves (Decleva et al., Chem. Phys., 1992, 168, 51) excitation energies and the shape of the spectra significantly. In this work, we systematically vary the underlying SCF approaches, that is, based on HF or density functional theory, to identify best suited reference orbitals using a series of small test molecules. We compare the energies of the K edges and NEXAFS spectra to experimental data. The main improvement compared to conventional CIS, that is, using HF ground state orbitals, is due to the electrostatic influence of the core hole. Different SCF approaches, density functionals, or the use of fractional occupations lead only to comparably small changes. Furthermore, to account for bigger systems, we adapt the core-valence separation for our approach. We demonstrate that the good quality of the spectrum is not influenced by this approximation when used together with the non-separated ground state wave function. Simultaneously, the computational demands are reduced remarkably. (C) 2016 Wiley Periodicals, Inc.
KW  - core excited states
KW  - configuration interaction
KW  - near edge X-ray absorption fine structure
Y1  - 2016
U6  - https://doi.org/10.1002/jcc.24531
SN  - 0192-8651
SN  - 1096-987X
VL  - 38
SP  - 116
EP  - 126
PB  - Wiley-Blackwell
CY  - Hoboken
ER  -