DENSITY-FUNCTIONAL CALCULATIONS ON WH6 AND WF6

We present the results of a computational study on both WH6 and WF6 us ing a relativistic pseudopotential on tungsten, comparing results at t he HF and MP2 levels with density functional calculations using local (SVWN), nonlocal (BLYP), and hybrid HF-DFT (ACM) functionals. In agree ment with the earlier all-electron HF study of Schaefer and co-workers (J. Chem. Phys. 1993, 98, 508), we find that the ground state geometr y of WH6 is far from octahedral; instead, there are four low-lying str uctures of C-3v (2) and C-5v (2) symmetry. Barrier heights for interco nversion of these isomers are low, indicating a highly fluxional molec ule. In contrast, the octahedral structure appears to be the only stab le species on the ground state potential energy surface of WF6. It der ives its stability from the greater ionic character of the W-F bond co mpared to that of W-H.