An analysis of the performance of coupled cluster methods for K-edge core excitations and ionizations using standard basis sets

Abstract

An extensive analysis has been carried out of the performance of standard families of basis sets with the hierarchy of coupled cluster methods CC2, CCSD, CC3 and CCSDT in computing selected Oxygen, Carbon and Nitrogen K-edge (vertical) core excitation and ionization energies within a core-valence separated scheme in the molecules water, ammonia, and carbon monoxide. Complete basis set limits for the excitation energies have been estimated via different basis set extrapolation schemes. The importance of scalar relativistic effects has been established within the spin-free exact two-component theory in its one-electron variant (SFX2C-1e).

Resonant Inelastic X-ray Scattering and Nonesonant X-ray Emission Spectra from Coupled-Cluster (Damped) Response Theory

“…[47][48][49][50][51] The intensity of the first excitation is also in very good agreement with the experimentally derived one, 48 whereas the intensity of the 2 1 A 1 excitation is overestimated. In the chosen basis set, and as previously observed, 53,54 the first two core excitation energies are systematically overestimated at the CCSD level, respectively by 1.74 eV and 1.67 eV, compared to the experimental peak maxima. This results in a slightly smaller separation between the two computed XAS peaks (1.79 eV) than the separation between the experimental peaks (1.9 eV).…”

Resonant Inelastic X-Ray Scattering and Non Resonant X-ray Emission Spectra from Coupled-Cluster (Damped) Response Theory

“…[43][44][45][46][47] The intensity of the first excitation is also in very good agreement with the experimentally derived one, 44 whereas the intensity of the 2 1 A 1 excitation is overestimated. In the chosen basis set, and as previously observed, 49,50 the first two core excitation energies are systematically overestimated at the CCSD level, respectively by 1.74 eV and 1.67 eV, compared to the experimental peak maxima. This results in a slightly smaller separation between the two computed XAS peaks (1.79 eV) than the separation between the experimental peaks (1.9 eV).…”

Spin adapted implementation of EOM-CCSD for triplet excited states: Probing intersystem crossings of acetylacetone at the carbon and oxygen K-edges

“…the aug-cc-pVTZ basis set, but with reduced computational cost, both in coupled cluster 11,40 and algebraic diagrammatic construction 41,42 theory.…”