title: Relativistic coupled-cluster calculations on XeF6: Delicate interplay between electron-correlation and basis-set effects.
abstract: A systematic relativistic coupled-cluster study is reported on the harmonic vibrational frequencies of the O(h), C(3v), and C(2v) conformers of XeF6, with scalar-relativistic effects efficiently treated using the spin-free exact two-component theory in its one-electron variant (SFX2C-1e). Atomic natural orbital type basis sets recontracted for the SFX2C-1e scheme have been shown to provide rapid basis-set convergence for the vibrational frequencies. SFX2C-1e as well as complementary pseudopotential based computations consistently predicts that both O(h) and C(3v) structures are local minima on the potential energy surface, while the C(2v) structure is a transition state. Qualitative disagreement between the present results for the O(h) structure and those from CCSD(T)-F12b calculations [Peterson et al., J. Phys. Chem. A 116, 9777 (2012)], which yielded a triply degenerate imaginary frequency for the O(h) structure, is attributed here to the high sensitivity of the computed harmonic frequencies of the t(1u) bending modes to the basis-set effects of triples contributions.
authors.affiliation: Department of Chemistry, Institute for Theoretical Chemistry, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Lan
authors.initials: L
authors.lastname: Cheng
authors.affiliation: Institut für Physikalische Chemie, Universität Mainz, D-55099 Mainz, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Gauss
authors.affiliation: Department of Chemistry, Institute for Theoretical Chemistry, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: John F
authors.initials: JF
authors.lastname: Stanton