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The geminal basis in explicitly correlated wave functions

Research output: Contribution to journalArticle

  • Sebastian Hoefener
  • David P. Tew
  • Wim Klopper
  • Trygve Helgaker
Original languageEnglish
Pages (from-to)25-30
Number of pages6
JournalChemical Physics
Volume356
Issue number1-3
DOIs
DatePublished - 17 Feb 2009

Abstract

In 1985 Kutzelnigg showed that a large percentage of the electron correlation energy for helium can be recovered using a single explicitly correlated basis function, chosen to fit the cusp at the correlation hole. In particular the simple wave function Psi = (1 + 1/2r(12))Phi returned more than 80% of the correlation energy. In this paper we return to Kutzelnigg's simple ansatz and remove the conventional double excitations in explicitly correlated CC2 theory (denoted as CCS(F12)), applying all established developments in modern F12 theory, such as replacing linear r(12) With f(r(12)) = exp(-gamma r(12)) and the use of auxiliary basis sets for the standard RI approximation in R12 theory. Analysing different approximations we show that in general the CCS(F12) approach yields 80-95% of the CC2 correlation energy, which is astonishingly large considering the small number and restricted form of the geminal basis functions. (C) 2008 Elsevier B.V. All rights reserved.

    Research areas

  • Explicit-correlation, Geminal basis set, Correlation factor, Correlation energy, Coupled-cluster, QUANTUM-CHEMICAL CALCULATIONS, MOLLER-PLESSET CALCULATIONS, ELECTRONIC-STRUCTURE THEORY, COUPLED-CLUSTER METHODS, BASIS-SETS, PERTURBATION-THEORY, LINEAR-R(12) CORRECTIONS, CORRELATION CUSP, TERMS, MULTIREFERENCE

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