Challenging systems for quantum chemistry : inorganic excited states and intermolecular aggregates
Almeida, Nuno Miguel da Silva
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This thesis focuses on challenging systems for computational chemistry: inorganic excited states and intermolecular aggregates. Excited states of inorganic systems can be extremely challenging for conventional methods of quantum chemistry, mostly due to strong correlation, degeneracy and near-degeneracy problems, in addition to a large density of states. A calibration study of the electronic excited states of a range of complexes has been carried out in a number of chapters using a wide range of methods. A range of all-electron and ECP basis sets were used. These calculations reveal the effect of improving the treatment of electron correlation systematically. A CASSCF/RASSCF study was performed for the most complex systems to be able to capture and analyse the multireference nature of the complexes. Later in the thesis the photochemistry arising from the photodissociaton of Mn2(CO)10 and Cr(CO)6 is described using CASPT2 to recover the dynamic correlation of the system and compare with previous CASSCF results. The last part focuses on intermolecular aggregates. Supramolecular structures have grown in importance in recent years due to their potential applications as advanced functional materials. The fine-tuning of these structures allows to build up higher hierarchical superstructures with very diverse and interesting properties. A bottom-up approach for this kind of systems is used to characterize the multichromophoric self-assembly of gels and detail their responses to light.