Multireference Correlation Calculations for the Ground States of VO^+/0/- Using Correlation Consistent Basis Sets

Abstract

Highly correlated multireference calculations for the ground states of the VO +/0/species are presented. We use extrapolation techniques to estimate correlation energies at the basis set limit. Correlation consistent basis sets for vanadium have been constructed for this purpose. Binding energies, bond distances, and vibrational frequencies have been calculated. Excellent agreement between the calculated and experimental values is reached for the cation and the neutral molecule. We present highly accurate theoretical estimates for the properties of the VO anion. Furthermore, we confirm previous assignments of its ground state which is found to be 3 Σ -.

A systematic quantum chemical investigation of the CH bond activation in methane by gas phase vanadium oxide cation VO+

“…8,23 Vibrational analysis and reaction path following calculations are used to classify and validate located critical (i.e. zero gradient) points of the PES.…”

“…Corresponding CASSCF calculations are equivalent to single determinant Hartree-Fock calculations for the triplet state. † Then we formally multiply the number of active orbitals and electrons by 2, 3, and 4, ending up with the active spaces (4,4), (6,6), and (8,8), respectively. In other words, we successively add one orbital from the closed shell space and one from the virtual space each time we enlarge the active space by a pair of electrons.…”

“…Note that the "high-spin" state is a quintet for the (4,4) active space, but a septet and a nonet for the (6,6) and (8,8) active spaces, respectively. The admixture of this "high-spin" state helps to control the nature of active orbitals: (1) it prevents often observed but undesired rotations between strongly occupied active and doubly occupied orbitals, and (2) improves the description of very weakly occupied active orbitals.…”

“…Their relative energies (with respect to the triplet structure of K) are obtained using (8,8) active space. Like just described earlier for the triplet state, molecular orbitals for each spin state are obtained from separate state-averaged CASSCF calculations for the state of the given spin multiplicity (i.e.…”

“…Our experience with bare vanadium oxide species 8,9 reveals that DFT calculations provide good molecular structures (geometries), but it must be taken with caution if energetic data is concerned. Therefore we decided to start a series of high level quantum chemical investigations on the gas phase interaction of vanadium oxide cations with small hydrocarbons.…”