Quantum Chemical Description of the Vibration Motion of Chrysene, Comparison Results of the MINDO/3-FORCES Method , ab initio and Density Functional (B3LYP)

Abstract

Vibration frequencies and IR absorption intensities for the chrysene molecule
in its calculated equilibrium structure were calculated quantum mechanically applying
both the semiempirical MINDO/3-FORCES, the ab initio and density functional
(B3LYP 6-311G) methods. The MINDO/3-FORCES frequency values were scaled
applying scaling factors that had been evaluated formerly for naphthalene, anthracene
and pyrene. Similarly the ab initio frequencies were scaled, and both treatments gave
vibration motions of correct symmetries and sequence in frequency values. The
calculated frequencies of MINDO/3-FORCES and scaled and ab initio methods, were
close to the literature experimental frequencies. The (B3LYP 6-311G) treatment
yielded frequency values that were very close to the experimental and MINDO/3-
FORCES forces frequencies. Comparison of the results for different vibration modes
showed a dependence of the vibration frequencies on the atomic site of the vibration.
Thus the following relations were detected: