DETAILED QUANTUMMECHANICAL CALCULATIONS OF MOLECULAR VIBRATION FREQUENCIES OF BENZENE, NAPHTHALENE, ANTHRACENE AND PHENANTHRENE - COMPARISON OF SEVERAL QUANTUMCHEMICAL METHODS

The reliability of the MNDO/PM3 semiempirical self-consistent field mo lecular orbital (SCF-MO) method for the calculation of fundamental vib ration frequencies, and the effect of scaling are studied. The vibrati on frequencies of naphthalene were calculated by various semiempirical SCF-MO methods like MNDO/PM3, AMI, and MINDO/3. Results from the ab i nitio STO-3G model are also included for comparison. The MNDO/PM3 freq uencies and geometries are in better agreement with experiment than th e other methods. The errors in the MNDO/PM3 frequencies of benzene, na phthalene, anthracene and phenanthrene are mostly characteristic for s pecific types of vibration. The mean percentage deviation is 5.5% for all the modes of the molecules under investigation. A scaling procedur e leads to frequency errors only within 2.8%. This agreement with expe riment offers hope that MNDO/PM3 calculations may usefully contribute to the determination of harmonic frequencies. Calculations of that typ e may be of practical use in assignments of vibrational frequencies, e specially for large molecules.