Current excited state methods can only describe excited states of a specific character or require technically demanding approaches. In this work, we demonstrate the usage of the projection-after-variation double-hybrid density functional theory method and the active space decomposition methodology for examining strongly correlated systems. The strengths and weaknesses of the projection-after-variation double-hybrid density functional theory method are discussed. Vertical excitation energies are computed for local, charge transfer, and Rydberg excited states. The findings of this study show that the proposed method can achieve standard deviations in the error of computed vertical excitation energies compared to complete active space second-order perturbation theory of similar size to linear response coupled-cluster theories for local excitations. This work also demonstrated the correlation between the magnitude of exchange and correlation provided within the method demonstrating that the predetermined parameters for double-hybrid functionals may not give the most accurate results. Single correlation methods like the projection-after-variation double-hybrid density functional theory method may not always be the most efficient way of studying systems with significant amounts of correlation. Thus, our work has also expanded to study active space decomposition, in which multiple nonorthogonal slater determinants are coupled to create a multiconfigurational method for molecular dimer systems. The active space decomposition method has been shown to achieve standard deviations close to that of complete active space second-order perturbation theory with a decreased computational cost in comparison to other multireference methods by selecting the most correlated slater determinants.

New method developments for the application of correlated electron systems

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.