Theoretical and experimental studies of optical nonlinearities of haloforms CHX3, X=F, Cl, Br, I

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Abstract
In this paper, we present ab initio calculations of static polarizability α and static first and second hyperpolarizabilities β and γ for the haloform series CHX3, where X=F, Cl, Br, and I using the effective core potential (ECP) approach. The microscopic optical nonlinearities α, β, and γ are calculated as the derivatives of the energy with respect to the electric field, with the energy determined by means of the self-consistent-field approach (SCF), and nonlinearities calculated by means of the coupled perturbed Hartree–Fock (CPHF) formalism. To test the approximation introduced by the ECP method, nonlinear optical responses for the lighter members of the series CHF3 and CHCl3 are compared with all electron calculations. The effects due to basis set size and inclusion of diffuse and polarization functions of d and f type are examined. The ECP technique is then used to calculate optical nonlinearities for CHBr3 and CHI3. Although very good agreement is found between calculated and experimental polarizabilities α for the haloform series, the agreement is not as good for the higher order polarizabilities. Possible causes for this discrepancy are discussed.