An explicitly correlated approach to basis set incompleteness in full configuration interaction quantum Monte Carlo

George H. Booth*, Deidre Cleland, Ali Alavi, David P. Tew

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

45 Citations (Scopus)

Abstract

By performing a stochastic dynamic in a space of Slater determinants, the full configuration interaction quantum Monte Carlo (FCIQMC) method has been able to obtain energies which are essentially free from systematic error to the basis set correlation energy, within small and systematically improvable error bars. However, the weakly exponential scaling with basis size makes converging the energy with respect to basis set costly and in larger systems, impossible. To ameliorate these basis set issues, here we use perturbation theory to couple the FCIQMC wavefunction to an explicitly correlated strongly orthogonal basis of geminals, following the [2](R12) approach of Valeev et al. The required one- and two-particle density matrices are computed on-the-fly during the FCIQMC dynamic, using a sampling procedure which incurs relatively little additional computation expense. The F12 energy corrections are shown to converge rapidly as a function of sampling, both in imaginary time and number of walkers. Our pilot calculations on the binding curve for the carbon dimer, which exhibits strong correlation effects as well as substantial basis set dependence, demonstrate that the accuracy of the FCIQMC-F12 method surpasses that of all previous FCIQMC calculations, and that the F12 correction improves results equivalent to increasing the quality of the one-electron basis by two cardinal numbers. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4762445]

Original languageEnglish
Article number164112
Number of pages11
JournalJournal of Chemical Physics
Volume137
Issue number16
DOIs
Publication statusPublished - 28 Oct 2012

Keywords

  • MULTIREFERENCE PERTURBATION-THEORY
  • COUPLED-CLUSTER THEORY
  • CORRELATION CUSP
  • GROUND-STATE
  • ELECTRONIC CORRELATION
  • DOUBLE-EXCITATIONS
  • WAVE-FUNCTIONS
  • SCF METHOD
  • TERMS
  • ENERGY

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