Transitions energies, optical oscillator strengths and partial potential energy surfaces of inner-shell states of water clusters

Transitions energies, optical oscillator strengths and partial potential energy surfaces of inner-shell (core-hole) states of water clusters are calculated at the inner-shell multiconfigurational self-consistent field (IS-MCSCF) level. This approach has been applied to diatomic and small polyatomic molecules with high accuracy. In the present work, IS-MCSCF was applied to molecular clusters for the first time. Discussions are carried out based on calculations done at different geometric conformations. It is shown that the transition energy is blue shifted to the first two discrete states at O 1s edge when referred to the isolated water molecule, while the core-electron binding energy is red shifted. Although the results for water clusters can only be compared to liquid water with care, it is worth emphasizing that this same trend is found in the corresponding spectra of the latter, revealing the importance of the first solvation shell to establish the main features of liquid water spectrum.