Semi empirical and ab initio methods for calculation of polarizability ( α) and the hyperpolarizability ( β) of fluorenyl molecular system: a comparative investigation

Abstract

The calculation of molecular hyperpolarizability of fluorenyl molecular system was investigated using both ab initio and semi empirical methods. Ab initio optimizations were performed at the Hartree–Fock level using different basis sets, starting with the minimal basis set and then moved to higher basis sets by inserting polarization and diffusion functions. The basis sets incorporated in this study include STO-3G, 3-21G, 6-31G, 6-31+G, 6-31++G, 6-31G(d,p), 6-31+G(d,p), 6-311G, 6-311+G and 6-311++G. The semi empirical investigation was confined to AM1, PM3, MNDO, MNDOd and the newly developed PM5 Hamiltonian. The first static hyperpolarizabilities were calculated at the Hartree–Fock level employing the corresponding basis sets using gaussian 98W. The semi empirical level calculations were performed using MOPAC 2002 within BioMedCAChe 6.1 software package. The first hyperpolarizability is dependent on the method of choice. The first hyperpolarizability, in general, is dependent on the choice of the basis set and clearly influenced after the addition of polarization and diffusion functions. The PM5 method produce results which are comparable with ab initio methodology with a very minimum computational cost.