An iterative variation-perturbation algorithm allowing a anharmonic vibrational treatment of polyatomic molecules is proposed. This state specific process consists on an iterative construction of small 3N-5 Vibrational Configuration Interation (VCI) matrixes (N being the number of atoms) with the most pertinent couplings and includes a perturbative treatment of the weakest contributions. Thus, this scheme allow to massively reduce the size of the CI matrixes with a minimum loss of correlation energy. Through the example of
, the results stemmed from the VCI-P process are compared to their full VCI counterpart. Moreover, the computations of anharmonic intensities are also implemented. As illustration, the modelization of the medium infrared (MIR) spectrum of the glycolaldehyde is reported.