title: High-order electron-correlation methods with scalar relativistic and spin-orbit corrections.
abstract: An assortment of computer-generated, parallel-executable programs of ab initio electron-correlation methods has been fitted with the ability to use relativistic reference wave functions. This has been done on the basis of scalar relativistic and spin-orbit effective potentials and by allowing the computer-generated programs to handle complex-valued, spinless orbitals determined by these potentials. The electron-correlation methods that benefit from this extension are high-order coupled-cluster methods (up to quadruple excitation operators) for closed- and open-shell species, coupled-cluster methods for excited and ionized states (up to quadruples), second-order perturbation corrections to coupled-cluster methods (up to triples), high-order perturbation corrections to configuration-interaction singles, and active-space (multireference) coupled-cluster methods for the ground, excited, and ionized states (up to active-space quadruples). A subset of these methods is used jointly such that the dynamical correlation energies and scalar relativistic effects are computed by a lower-order electron-correlation method with more extensive basis sets and all-electron relativistic treatment, whereas the nondynamical correlation energies and spin-orbit effects are treated by a higher-order electron-correlation method with smaller basis sets and relativistic effective potentials. The authors demonstrate the utility and efficiency of this composite scheme in chemical simulation wherein the consideration of spin-orbit effects is essential: ionization energies of rare gases, spectroscopic constants of protonated rare gases, and photoelectron spectra of hydrogen halides.
authors.affiliation: Quantum Theory Project, Department of Chemistry, University of Florida, Gainesville, Florida 32611-8435, USA. hirata@qtp.ufl.edu
authors.forename: So
authors.initials: S
authors.lastname: Hirata
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yanai
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Harrison
authors.forename: Muneaki
authors.initials: M
authors.lastname: Kamiya
authors.forename: Peng-Dong
authors.initials: PD
authors.lastname: Fan