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The Development, Implementation and Application of Accurate Quantum Chemical Methods for Molecular Structure, Spectra and Reaction Paths

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Technical Report

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University of Florida - Gainesville Gainesville United States

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A number of new developments in coupled-cluster theory and their implementation into the massively parallel ACES 3 and 4 systems were accomplished. Studies were made of the singlet-triplet energy separations in di-radicals using the recently developed DIPDEA-EOM-CC which is a straight-forward approach to classes of multi-reference problems in coupled-cluster CC theory. As a target for future multi-reference problems, transition metal multiplets were also studied with single reference coupled-cluster, subject to a variety of orbital choices. In particular, the use of fractionally occupied orbitals termed template orbitals were introduced, which could then be occupied however necessary to describe a multiplet state, depending upon CC theory to fix the orbitals as part of the calculation. The length at which an all transalkane-like C18H38 can turn on itself to form a hairping was also investigated. The formation of such a kink requires only 0.5 kcalmol, so very high accuracy is demanded. The coupled-cluster methods in ACES III make such a study possible. The decomposition of RDX has been studied in detail to assess the energetics of the gas phase decomposition paths. Comparison to HMX and CL20 have been part of the study. Another study focused on the sway a strong bond link in oxalate can be broken by manganese containing enzymes. The intermediate steps involved the formation of either a radical or radical anion. In this way the activation barrier could be reduced from 36 kcalmol to less than10.

Subject Categories:

  • Quantum Theory and Relativity

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