  Vibrationally resolved near-edge x-ray absorption spectra at the K-edge for a
number of small molecules have been computed from anharmonic vibrational
configuration interaction calculations of the Franck-Condon factors. The
potential energy surfaces for ground and core-excited states were obtained at
the core-valence separated CC2, CCSD, CCSDR(3), and CC3 levels of theory,
employing the Adaptive Density-Guided Approach (ADGA) scheme to select the
single points at which to perform the energy calculations. We put forward an
initial attempt to include pair-mode coupling terms to describe the potential
of polyatomic molecules
