Výpočty metodou renormalizační grupy matice hustoty a optimalizace entanglementu v kvantové chemii

Antalík, Andrej

Density matrix renormalization group is a powerful numerical approach originating in solid state physics. Since its introduction to quantum chemis- try it has been successfully applied to many challenging problems and proved especially efficient for systems with strong multi-reference character. As the method is not invariant to the change of orbital ordering, we implemented the automatic orbital ordering optimization procedure built around the entan- glement analysis and employing the Fiedler method. A technique for active space selection based on one-orbital entropy is introduced. We followed the study by Berardo et al. in which EOM-CC methods were applied to excited states of TiO2 clusters. Four lowest-lying singlet excited states of monomer, dimer and trimer were calculated by means of the DMRG method. In case of the monomer there was good agreement for two states, but the calculations suffered from insufficient treatment of dynamic correlation. For the dimer our results were in very good agreement with EOM-CCSDT results and for the trimer further study would be appropriate. 1

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