Theoretical study on oligoacenes and polycyclic aromatic hydrocarbons using the restricted active space self-consistent field method.
ABSTRACT This is the first study, to my knowledge, to report the optimized geometries and vibrational frequency analysis for oligoacenes (naphthalene, anthracene, naphtacene, and pentacene) and polycyclic aromatic hydrocarbons (PAHs; perylene, phenanthrene, and picene) by using the restricted active space self-consistent field (RASSCF) method. For naphthalene, both the complete active space self-consistent field (CASSCF) and RASSCF calculations were performed. As a result, it was confirmed that the RASSCF, with its small computational costs, is appropriate for oligoacenes and PAHs. It should be noted that, for anthracene and perylene, the optimized geometries under D(2h) symmetry were not the minimum energy points, whereas the optimized geometries under C(s) symmetry were the minimum energy points. For naphthalene, anthracene, naphtacene, pentacene, and phenanthrene, the calculated bond lengths and infrared absorption spectra by the RASSCF were in good agreement with the experimental values.