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Study of Diradicals By Explicitly Correlated Multireference Coupled Cluster Methods
Švaňa, Matej ; Pittner, Jiří (advisor) ; Pitoňák, Michal (referee)
Title: Study of Diradicals by Explicitly Correlated Multireference Coupled Cluster Methods Author: Matej Švaňa Department: Department of Physical and Macromelecular Chemistry Supervisor: Mgr. Jiří Pittner, Dr. rer. nat., J. Heyrovský Institute of Physical Chemistry Abstract: Total energies of cyclopropane, trimethylene, and propylidene were calculated with conventional post-HF CCSD(T), BWCCSD(T), MkCCSD(T) methods and their explicitly correlated alternatives. Main aims of the the- sis were to compare the basis set convergence of total energies and relative energies between cyclopropane and trimethylene/propylidene, both at the conventional and the explicitly correlated levels. It was shown that use of explicit correlation accelerates the convergence of the total energy by one or- der of basis set quality, resulting in considerable savings in computational times. Also, the MkCCSD(T)-F12/QZ and the BWCCSD(T)-F12/QZ calcula- tions belong to the most sophisticated approaches employed for estimation of the relative energies of cyclopropane and trimethylene/propylidene to date. Keywords: explicitly correlated, coupled cluster, multi-reference, cyclopropane isomerisation, trimethylene, propylidene 1
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Explicitly correlated multireference coupled cluster computations
Švaňa, Matej ; Pittner, Jiří (advisor) ; Nachtigall, Petr (referee)
Title: Explicitly Correlated Multireference Coupled Cluster Computations Author: Matej Švaňa Department: Department of Physical and Macromelecular Chemistry Supervisor: Mgr. Jiří Pittner, Dr. rer. nat., J. Heyrovský Institute of Physical Chemistry Abstract: Total energies for the bent singlet state of carbene molecule were calculated using post-HF CCSD, CCSD-F12, MR BWCSSD, and MR BWCC- SD-F12 methods. Main aim of the thesis was to compare the energy con- vergence with respect to cardinal number X of the basis set used for the conventional MR BWCCSD method and its explicitly correlated counter- part. Also, weights of the references within the multireference calculations were compared. It was shown that use of explicit correlation within the mul- tireference approach, as well as for the single-reference approach, speeds up the convergence of energy by an order when considering the cardinal number of basis set. Keywords: coupled clusters, multireference, explicitly correlated, F12, car- bene 1
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