TDDFT and the X-ray absorption spectrum of liquid water: finding the “best” functional

We investigate the performance of time-dependent density functional theory (TDDFT) for reproducing high-level reference X-ray absorption spectra of liquid water. For this, we apply the integrated absolute difference (IAD) metric, previously used for X-ray emission spectra of liquid water [J. Chem. Theory Comput. 19, 7333-7342 (2023)], in order to investigate which exchange-correlation (xc) functionals yield TDDFT spectra in best agreement to reference, as well as to investigate the suitability of IAD for XAS spectrum calculations. It is seen that long-range corrected xc-functionals are required to yield good agreement with reference coupled cluster (CC) and algebraic-diagrammatic construction (ADC) spectra, with 100% asymptotic Hartree−Fock exchange resulting in the lowest IADs. The xc-functionals with best agreement to reference have been adopted for larger water clusters, yielding results in line with recently published coupled cluster theory, but which still show some discrepancies in the relative intensity of the features compared to experiment.