Journal
JOURNAL OF COMPUTATIONAL CHEMISTRY
Volume 40, Issue 19, Pages 1789-1799Publisher
WILEY
DOI: 10.1002/jcc.25832
Keywords
configuration interaction; excited states; X-ray spectroscopy; multiconfigurational wavefunction; computational cost
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Funding
- foundation Olle Engkvist Byggmastare
- Carl Trygger Foundation
- Knut and Alice Wallenberg Foundation [KAW-2013.0020]
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Electronically excited states play important roles in many chemical reactions and spectroscopic techniques. In quantum chemistry, a common technique to solve excited states is the multiroot Davidson algorithm, but it is not designed for processes like X-ray spectroscopy that involves hundreds of highly excited states. We show how the use of a restricted active space wavefunction together with a projection operator to remove low-lying electronic states offers an efficient way to reach single and double-core-hole states. Additionally, several improvements to the stability and efficiency of the configuration interaction (CI) algorithm for a large number of states are suggested. When applied to a series of transition metal complexes the new CI algorithm does not only resolve divergence issues but also leads to typical reduction in computational time by 70%, with the largest savings for small molecules and large active spaces. Together, the projection operator and the improved CI algorithm now make it possible to simulate a wide range of single- and two-photon spectroscopies. (c) 2019 Wiley Periodicals, Inc.
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