title: Discontinuities-free complete-active-space state-specific multi-reference coupled cluster theory for describing bond stretching and dissociation.
abstract: The earlier proposed multi-reference state-specific coupled-cluster theory with the complete active space reference [CASCC; Lyakh et al., J. Chem. Phys. 122, 024108 (2005)] suffered from a problem of energy discontinuities when the formal reference state was changing in the calculation of the potential energy curve (PEC). A simple remedy to the discontinuity problem is found and is presented in this work. It involves using natural complete active space self-consistent field active orbitals in the complete active space coupled-cluster calculations. The approach gives smooth PECs for different types of dissociation problems, as illustrated in the calculations of the dissociation of the single bond in the hydrogen fluorine molecule and of the symmetric double-bond dissociation in the water molecule.
authors.affiliation: Department of Chemistry, V. N. Karazin Kharkiv National University, Kharkiv, Ukraine.
authors.forename: Irina A
authors.initials: IA
authors.lastname: Zaporozhets
authors.affiliation: Department of Chemistry, V. N. Karazin Kharkiv National University, Kharkiv, Ukraine.
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Ivanov
authors.affiliation: Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Dmitry I
authors.initials: DI
authors.lastname: Lyakh
authors.affiliation: Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Ludwik
authors.initials: L
authors.lastname: Adamowicz