Gaussian basis sets for ab initio calculation of NLO properties of polyatomic molecules

In this paper, basis sets for H, C, N and O atoms were adjusted to obtain electric properties of diatomic molecules. The dipole moment, polarizability and first-order hyperpolarizability were calculated for H₂, CH⁺, CN^- and CO molecules and the basis sets modified to reproduce the reference data available. A sequential methodology was used, where the basis set for H is firstly adjusted and then used to fit the basis set for C in the CH⁺ molecule and so on. The final basis sets were (7s2p1d)→[3s2p1d] for H and (9s5p2d)→[5s3p2d] for C and O. In the case of N atom, the best basis set was found to be (9s5p1d)→[5s3p1d], where only one set of d polarization functions was needed. The atomic basis sets fitted were further utilized for calculation of geometry and electric properties of 36 benzene derivatives mono- and di-substituted by electron donor and acceptor groups attached at ortho, meta and para positions. The results were satisfactory for most of molecules. For instance, in the case of p-nitroaniline, an important push-pull benzene derivative, the first hyperpolarizability was predicted to be 9.4 × 10^-30 e.s.u. in excellent agreement with experimental value, 9.2 × 10^-30 e.s.u.. Besides electric properties, our basis sets also gave good geometries for polyatomic molecules at reasonable computational cost. Therefore, the results reported in the present paper suggest the use of our modified basis sets for calculation of geometry and electric properties (linear and non-linear) of push-pull benzene derivatives like molecules.