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.
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ABSTRACT: A systematic approach is introduced for defining Restricted Active Space Self-Consistent-Field (RASSCF) orbitals for treating multiple electronic states in a balanced way, based on an SCF state-averaging procedure (Thom and Head-Gordon, 2008). We start from an SCF density matrix averaged over the electronic states of interest and choose a RAS partition based on the corresponding natural orbital occupation numbers. In order to test this procedure, we apply it to naphthalene cation, previously studied as a potential interstellar Polycyclic Aromatic Hydrocarbon (PAH) because of its photo stability following electronic excitation (Hall et al., 2006). The results obtained with this method in terms of energies and bond lengths for the first three electronic states and the corresponding minimum energy conical intersections between potential energy surfaces compare very well with CASSCF results and suggest further testing of the method for RASSCF calculations.Computational and Theoretical Chemistry 07/2014; · 1.14 Impact Factor