Multireference X-ray emission and absorption spectroscopy calculations from Monte Carlo configuration interaction

Abstract

We adapt the method of Monte Carlo configuration interaction to calculate core-hole states and use this for the computation of X-ray emission and absorption values. We consider CO, CH 4 , NH 3 , H 2 O, HF, HCN, CH 3 OH, CH 3 F, HCl and NO using a 6-311G** basis. We also look at carbon monoxide with a stretched geometry and discuss the dependence of its results on the cutoff used. The Monte Carlo configuration interaction results are compared with EOM-CCSD values for X-ray emission and with experiment for X-ray absorption. Oscillator strengths are also computed and we quantify the multireference nature of the wavefunctions to suggest when approaches based on a single reference would be expected to be successful.

Assessment of basis sets for density functional theory-based calculations of core-electron spectroscopies

“…Within the context of quantum chemical calculations, core-electron binding energies (CEBEs) are most commonly computed using a self-consistent field ( SCF) approach [6][7][8][9], although an unrestricted generalised transition state method has also been proposed for the calculation of CEBEs [10,11]. X-ray absorption spectra can be computed using the transition potential method [12], time-dependent density functional theory (TDDFT) [13,14], Bethe-Salpeter equation [15], coupled cluster theory [16,17], the algebraic diagrammatic construction (CVS-ADC) scheme [18] and multi-reference methods [19]. TDDFT and EOM-CCSD methods have also been used to study X-ray emission spectroscopy through the use of a reference determinant with a core-hole [20][21][22][23].…”

XABOOM: An X-Ray Absorption Benchmark of Organic Molecules Based on Carbon, Nitrogen, and Oxygen 1s → π ∗ Transitions

“…An abundance of methodologies for modeling X-ray absorption spectra has been developed, including semi-empirical, density-based, and wave function-based methods. 31,33,34,[36][37][38][39]43,45,[49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68] Here the focus is on first-principles methods, and hence semi-empirical approaches will thus be left out of the discussion. Among the first-principles methods, researchers in the field of theoretical spectroscopy commonly apply density functional theory (DFT).…”

“…Moving to wave function-based methods, single-and multi-reference methods have both been used, and electron relaxation can be accounted for through electron correlation by the use of (at least) doubly excited configurations. [34][35][36]51,53,54,56,68,[94][95][96][97][98][99] Available schemes include single-reference methods such as coupled cluster (CC) theory, the algebraic-diagrammatic construction (ADC) approach, density-cumulant theory, and multireference methods such as RASSCF, RASPT2, and MR-CC. Regardless of the underlying electronic structure method used, a reoccurring issue for any method based on molecular response theory is the embedding of core-excited states in the continuum of valence-excited states, which makes a straightforward application of an iterative diagonalization scheme such as the Davidson algorithm 100 unfeasible for all but the smallest of systems.…”

Development of spin‐orbit coupling for stochastic configuration interaction techniques

“…Excellent results were obtained for the H 3 molecule. Finally, other applications of MCCI include calculations of higher‐order dipole properties, X‐ray emission and absorption energies, positronic systems, and the potential energy surfaces of transition metal dimers …”