Strong static and dynamic Jahn-Teller and pseudo-Jahn-Teller effects in niobium tetrafluoride.

We present a first-principles study of the static and dynamic aspects of the strong Jahn-Teller (JT) and pseudo-JT (PJT) effects in niobium tetrafluoride, NbF, in the manifold of its electronic ground state, E, and its first excited state, T. The complex topography of the full-dimensional multi-sheeted adiabatic JT/PJT surfaces is analyzed computationally at the complete-active-space self-consistent-field (CASSCF) and multireference second-order perturbation levels of electronic structure theory, providing a detailed characterization of minima, saddle points, and minimum-energy conical intersection points. The calculations reveal that the tetrahedral (T) configuration of NbF undergoes strong JT distortions along the bending mode of e symmetry, yielding tetragonal molecular structures of D symmetry with T → D stabilization energies of about 2000 cm in the X̃E state and about 6400 cm in the ÃT state.

First-principles study of large-amplitude dynamic Jahn-Teller effects in vanadium tetrafluoride.

Transition metal tetrahalides are a class of highly symmetric molecules for which very few spectroscopic data exist. Exploratory ab initio calculations of electronic potential energy functions indicate that the equilibrium molecular geometries of the vanadium, niobium, and tantalum tetrafluorides (i.e.

Composite vibrational spectroscopy of the group 12 difluorides: ZnF2, CdF2, and HgF2.

The vibrational spectra of group 12 difluorides, MF2 (M = Zn, Cd, Hg), were investigated via coupled cluster singles, doubles, and perturbative triples, CCSD(T), including core correlation, with a series of correlation consistent basis sets ranging in size from triple-zeta through quintuple-zeta quality, which were then extrapolated to the complete basis set (CBS) limit using a variety of extrapolation procedures. The explicitly correlated coupled cluster method, CCSD(T)-F12b, was employed as well. Although exhibiting quite different convergence behavior, the F12b method yielded the CBS limit estimates closely matching more computationally expensive conventional CBS extrapolations.