Extending relativistic linear response theory to address solvent effects

Sammanfattning: The central aim of this thesis is to derive, implement and test new methods to calculate various types of spectroscopies of compounds containing heavy elements in an aqueous environment. Methods that can target such systems have to consider the following:(i) It is crucial to take relativistic effects into account.(ii) Modeling of larger systems is expensive in quantum chemistry. Thus, cheaper options need to be consideredfor the water solvent.(iii) Methods to calculate electronic spectra have to be able to model electronic excitations properly.(i) The relativistic effects can be obtained by solving the Dirac equation. This yields a four-component wave function, but methods based on only two-components have been developed in this thesis. (ii) Larger systems can be tackled by dividing them into a region that is treated by methods from electronic structure theory, and a larger environment that is treated classically as a collection of localized static multipole moments (charges, dipole moments, etc.). In most such hybrid schemes (called QM/MM) we only take into account how the static multipole moments in the environment influence the wave function in the QM region. In this thesis, however, we allow mutual polarization of the regions through the polarizable embedding (PE) model. (iii) We calculate excited state properties through linear response theory. This has been developed to work with a variety of approximate state wave functions and has been extended to a relativistic framework. Moreover, it has been combined with PE. Yet, regular linear response theory suffers from problems in non-resonant regions of spectra. For this, we consider a variant of linear response theory, called the complex polarization propagator. Here, the life-times of the excited states are included in the response equations. This allows the calculation of spectra in regions that are problematic in regular response theory. In this thesis, we have devised a method that combines relativistic CPP within a polarizable embedding framework. We employ the method on light-activated platinum complexes with application in chemotheraphy. Here, both relativistic and solvent effects are crucial to model the excitation processes. Moreover, we also consider the calculation of electronic circular dichroism for chiral organic molecules that contain heavy elements like iodine.