Derivation and application of response functions for nonlinear absorption and dichroisms

Sammanfattning: This thesis is titled ’Derivation and application of response functions for nonlinear absorption and dichroisms’ and was written by Tobias Fahleson at the Division of Theoretical Chemistry & Biology at KTH Royal Institute of Technology in Sweden. It explores and expands upon theoretical means of quantifying a number of nonlinear spectroscopies, including two-photon absorption, resonant inelastic x-ray scattering, Jones birefringence, and magnetic circular dichroism. Details are provided for the derivation and program implementation of complex-valued (damped) cubic response functions that have been implemented in the quantum chemistry package DALTON [1], based on working equations formulated for an approximate-state wave function. This is followed by an assessment of the implementation. It is demonstrated how two-photon absorption (TPA) can be described either through second-order transition moments or the damped cubic response function. A set of illustrative TPA profiles are produced for smaller molecules. In addition, resonant inelastic x-ray scattering (RIXS) is explored in a similar manner as two-photon absorption. It is shown for small systems how RIXS spectra may be obtained using a reduced form of the cubic response function. Linear birefringences are investigated for noble gases, monosubstituted benzenes, furan homologues, and liquid acetonitrile. Regarding the noble gases, the Jones effect is shown to be proportional to a power series with respect to atomic radial sizes. For monosubstituted benzenes, a linear relation between the Jones birefringence and the empirical para-Hammett constant as well as the permanent electric dipole moment is presented. QM/MM protocols are applied for a pure acetonitrile liquid, including polarizable embedding and polarizable-density embedding models. The final chapter investigates magnetically induced circular dichroism (MCD). A question regarding relative stability of the first set of excited states for DNA-related molecular systems is resolved through MCD by exploiting the signed nature of circular dichroisms. Furthermore, to what extent solvent contributions affect MCD spectra and the effect on uracil MCD spectrum due to thionation is studied.