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Simon Eckard, Thomas E. Exner
Generalized Hybrid Orbitals in the FA-ADMA Method
Keywords: Ab-Initio Quality, Fuzzy Density Fragmentation, QM/MM, Border Region, Proteins
The field-adapted adjustable density matrix assembler (FA-ADMA), developed for ab initio quality quantum chemistry computations of proteins and other macromolecules, divides a molecule (the target) into fuzzy fragments. For these fragments, conventional quantum chemical calculations are performed using moderate-sized “parent molecules”, which contain both the fragment and all the local interactions of the fuzzy fragment with its surroundings within a pre-selected distance. Effects of distant parts of a target macromolecule are approximated in the fragment by point charges in the quantum chemical calculations. A known problem of the FA-ADMA approach, as well as mixed QM/MM calculations, is the treatment of the border between the quantum region and the point charges. One possibility in circumventing this problem is to use generalized hybrid orbitals (GHO) on the boundary atom next to the QM region. In this paper we describe the introduction of this approach in the FA-ADMA method, which includes a re-parameterization of the partial charges of the boundary atom. Four small proteins were taken as test cases to compare the new GHO-FA-ADMA to the original hydrogen-capping-atom scheme. The promising results demonstrate that, after the extension to sp2-hybridized atoms, GHO could greatly increase the accuracy of FA-ADMA calculations.
Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag
Print ISSN: 0942-9352
Volume: 220, 07/2006
Pages: 927 - 944