| dc.description.abstract | The atomistic description of complex molecular systems, such as solutions and biological moieties, requires some sort of compromise between computational efforts and accuracy. Low-level models can treat thousands of atoms, but under severe approximations that neglect important features of the systems. High-level models can give a more accurate description, but with stricter size limitations. In order to try taking the best from the different approaches, multiscale methods have been developed: high levels of theory are used on the part of the system directly responsible for the property of interest, while low levels of theory are employed for the environment. The first part of this thesis is about the implementation and optimization of one of these multiscale approaches, the multilevel Hartree-Fock model. The region of interest is treated with the Hartree-Fock method, and the environment is frozen and considered as an external field. The implementation is now publicly available in the software eT. The time and memory required for calculations have been reduced to grow linearly with the number of atoms.In the second part, the multilevel Hartree-Fock model has been used in combination with other theoretical methods, of both higher and lower levels, to study the properties of complex systems. In particular, the resulting three and four-level approaches have been applied to the calculation of excitation energies and polarizabilities of molecules in solution.
In the future, these protocols are expected to be further applied to the study of local properties in systems of interest for biology and material science. | en_US |
