Ab initio calculation of dipole polarizabilities for nonlinear optics applications

In the field of photonics, the analog of electronics, which describes the technology of using photons to acquire, store, transmit, and process information, molecules with large dipole polarizabilities and hyperpolarizabilities are of interest. Ab initio calculations of dipole polarizabilities (DP) and hyperpolarizabilities (DH) of systems of model molecules enhances greatly the development process of new materials and ultimately the fabrication of devices which implement photonics. Ab initio calculations at the Hartree Fock (HF) self-consistent field (SCF) level and at the second-order Moller Plesset Perturbation Theory level (MP2) using the Hondo 8 (H8) and Gaussian 90 (G90) computer codes are performed to calculate accurate values of the dipole moment (DM), dipole polarizabilities (DP), first and second dipole hyperpolarizabilities (DH) for a series of small polyatomic molecules. These are the following: AH₃; (A = N, P, As), formamide, benzene, pyridine, pyrrole, AH₂; (A = S, Se, Te), AH₄;, A₂;H₄;, and A₂;H₂; (A = C, Si, Ge). The pyrrole calculations show how the effective core potential (ECP) could be used to produce reasonably accurate results. Accurate HF SCF calculations using very large basis sets are used as reference results, which are used to develop much smaller basis sets without significant loss in accuracy of results. It was found that the MP2 calculations produced significant changes in the results. Typically, the DP increases by 10- 20%, the second DH (y tensors) increases 20-40%, and the first DH (ẞ tensors) changes by 100%, and sometimes changes in sign. For example, a H₂;Te [11s10p8d1f/4s2p2d] basis set calculation β_yyz; changes from 21.88 (HF) to -6.38 (MP2).