ABSTRACT
Molecular modelling is considered to be an effective tool for the evaluation of many physical as well as spectroscopic parameters. Both Semiempirical AMI, PM5 and ab initio methods. VWN. B88LYP B88PW91. B3PW9I and B3LYP were used to study nitromethane in its gas phase. The optimized structure, some physical parameters and vibrational spectrum are calculated and discussed. The calculated optimized structure indicates that nitromethane belongs to point group C[2v]. The obtained data indicate that quantum mixing gives results comparable to both ab initio method in accuracy and semiempirical method in computation time. It is concluded that for a small structure like nitromethane quantum mixing method provides reliable results in short computation time