Similar to NH 3 , the XAS spectrum for H 2 O is richer relative to the X2PA spectra (from both the CVS-0 and CVS-uS approaches) and dominated by the three features around 534.0 eV, 535.7 eV, and 537.0 eV. The first feature results from the XA 1 → c1A 1 transition, the second from the XA 1 → c1B 1 transition, and the third from XA 1 → c1B 2 and XA 1 → c2A 1 transitions, see also Refs. 73,93. The X2PA spectrum for both the CVS-0 and CVS-uS has a dominant peak corresponding to the XA 1 → c1A 1 transition with a tail of small features observed in the high-energy region. The CVS-uS X2PA spectrum is also similar to the X2PA spectrum in Ref. 63.