title: On Pair Functions for Strong Correlations.
abstract: The UHF wave function may be written as a spin-contaminated pair wave function of the APSG form, and the overlap of the α and β corresponding orbitals of the UHF solution can be taken as a proxy for the strength of the correlation captured by breaking symmetry. We demonstrate this with calculations on one- and two-dimensional hydrogen clusters and make contact with the well studied Hubbard model. The UHF corresponding orbitals pair in a manner that allows a smooth evolution from doubly occupied orbitals at small distance to one in which wave function breaks symmetry, segregating the α and β electrons onto distinct sublattices at large distances. By performing spin projection on these UHF solutions, we address strong correlations that are difficult to capture at intermediate distances using a single determinant.
authors.affiliation: Theoretical Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Jason K
authors.initials: JK
authors.lastname: Ellis
authors.affiliation: Theoretical Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Martin
authors.affiliation: Department of Chemistry and Department of Physics and Astronomy, Rice University , Houston, Texas 77005-1827, United States.
authors.forename: Gustavo E
authors.initials: GE
authors.lastname: Scuseria