Article
Adiabatic connection for strictly correlated electrons.
Department of Chemistry, University of California, Irvine, California 926972025, USA.
The Journal of Chemical Physics (Impact Factor: 3.12). 09/2009; 131(12):124124. DOI: 10.1063/1.3239472 Source: arXiv

Article: The formulation and performance of a perturbative correction to the perfect quadruples model.
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ABSTRACT: A recently published alternative hierarchy of coupledcluster approximations is reformulated as a perturbative correction. A single variant, a model for the total electronic energy based on the perfect quadruples model, is explored in detail. The computational scaling of the method developed is the same as canonical second order Mo̸llerPlesset perturbation theory (fifth order in the number of molecular orbitals), but its accuracy competes with the highaccuracy, highcost standard CCSD(T), even when the latter is allowed to break spinsymmetry. The variation presented can be implemented without explicit calculation and storage of the most expensive energy contributions, thereby improving the range of systems which can be treated. The performance and scaling of the method are demonstrated with calculations on the water, fluorine, and oxirane molecules, and compared to the parent model.The Journal of Chemical Physics 04/2011; 134(15):154112. · 3.12 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Improving the accuracy and thus broadening the applicability of electronic density functional theory (DFT) is crucial to many research areas, from material science, to theoretical chemistry, biophysics and biochemistry. In the last three years, the mathematical structure of the stronginteraction limit of density functional theory has been uncovered, and exact information on this limit has started to become available. The aim of this paper is to give a perspective on how this new piece of exact information can be used to treat situations that are problematic for standard KohnSham DFT. One way to use the stronginteraction limit, more relevant for solidstate physical devices, is to define a new framework to do practical, nonconventional, DFT calculations in which a stronginteracting reference system is used instead of the traditional noninteracting one of Kohn and Sham. Another way to proceed, more related to chemical applications, is to include the exact treatment of the stronginteraction limit into approximate exchangecorrelation energy density functionals in order to describe difficult situations such as the breaking of the chemical bond.Physical Chemistry Chemical Physics 10/2010; 12(43):1440519. · 4.20 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Paired, activespace treatments of static correlation are augmented with additional amplitudes to produce a hierarchy of parsimonious and efficient cluster truncations that approximate the total energy. The number of parameters introduced in these models grow with system size in a tractable way: two powers larger than the static correlation model it is built upon: for instance cubic for the models built on perfect pairing, fourth order for a perfect quadruples (PQ) reference, and fifth order for the models built on perfect hextuples. These methods are called singles+doubles (SD) corrections to perfect pairing, PQ, perfect hextuples, and two variants are explored. An implementation of the SD methods is compared to benchmark results for F(2) and H(2)O dissociation problems, the H(4) and H(8) model systems, and the insertion of beryllium into hydrogen. In the cases examined even the quartic number of parameters associated with PQSD is able to provide results which meaningfully improve on coupledcluster singles doubles (CCSD) (which also has quartic amplitudes) and compete with existing multireference alternatives.The Journal of Chemical Physics 09/2010; 133(12):124102. · 3.12 Impact Factor
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