Vibrational spectra for P4O6 and P4O10 systems: Theoretical study from DFT quartic potential and mixed perturbation-variation method

This Letter presents the first anharmonic vibrational results obtained for the tetraphosphorus hexoxide and the tetraphosphorus decaoxide from PBE0/DFT calculations using a 6-311+G(2d) basis set. The quartic force fields are obtained from a linear regression procedure taking into consideration energies and analytical gradients and hessians. The vibrational energies levels are computed using a mixed variation-perturbation approach (VCI-P) in which the vibrational configuration interaction (VCI) space is guessed by a preliminary second order perturbative (P) treatment. Our theoretical results are compared with the existing Raman and IR data for a new vibrational analysis.