Ab initio and density functional calculations of core excitation spectra of CO, H2CO and F2CO

Calculations of the discrete core excitation spectra, including Rydberg transitions, are reported for CO, H2CO and R2CO employing ab initio and density functional approaches. The highly correlated QDPTCI approach compares well with experimental data and other accurate ab initio results. It appears that reliable values can be currently obtained for small molecules, although considerable uncertainty still affects intensity values, notably those experimentally derived. Comparison with the simpler Ih-lp CI approach indicates some deficiencies of the latter, attributed to the use of inadequate orbitals. The density functional approach proves generally reliable and can be profitably employed for the interpretation of experimental data in large systems, although presently limited to the case of nondegenerate core holes.