title: Electronic correlation without double counting via a combination of spin projected Hartree-Fock and density functional theories.
abstract: Several schemes to avoid the double counting of correlations in methods that merge multireference wavefunctions with density functional theory (DFT) are studied and here adapted to a combination of spin-projected Hartree-Fock (SUHF) and DFT. The advantages and limitations of the new method, denoted SUHF+fcDFT, are explored through calculations on benchmark sets in which the accounting of correlations is challenging for pure SUHF or DFT. It is shown that SUHF+fcDFT can greatly improve the description of certain molecular properties (e.g., singlet-triplet energy gaps) which are not improved by simple addition of DFT dynamical correlation to SUHF. However, SUHF+fcDFT is also shown to have difficulties dissociating certain types of bonds and describing highly charged ions with static correlation. Possible improvements to the current SUHF+fcDFT scheme are discussed in light of these results.
authors.affiliation: Department of Chemistry, Rice University, Houston, Texas 77251-1892, USA.
authors.forename: Alejandro J
authors.initials: AJ
authors.lastname: Garza
authors.affiliation: Department of Chemistry, Rice University, Houston, Texas 77251-1892, USA.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Jiménez-Hoyos
authors.affiliation: Department of Chemistry and Department of Physics and Astronomy, Rice University, Houston, Texas 77251-1892, USA and Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia.
authors.forename: Gustavo E
authors.initials: GE
authors.lastname: Scuseria