title: On the evaluation of quadratic response functions at the four-component Hartree-Fock level: nonlinear polarization and two-photon absorption in bromo- and iodobenzene.
abstract: The nonlinear polarization and two-photon absorption parameters have been determined for dibromo- and di-iodobenzene in their meta- and ortho-conformations and with relativistic effects accounted for to a varying degree. By exclusion of small component integrals in the calculations of the first-order hyperpolarizability, results within 1% of fully relativistic four-component Hartree-Fock values are obtained at a cost of 8.7 times the corresponding nonrelativistic calculations. It is shown that the nonlinear absorption in bromobenzene (and even more so in iodobenzene) is broad banded due to spin-orbit interactions among the excited states, and nonrelativistic and scalar relativistic calculations are not to be used in this case.
authors.affiliation: Department of Physics, Chemistry, and Biology, Linköping University, SE-581 83 Linköping, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Henriksson
authors.forename: Ulf
authors.initials: U
authors.lastname: Ekström
authors.forename: Patrick
authors.initials: P
authors.lastname: Norman