Density Functional Calculations on WH6 and WF6

Abstract

We present the results of a computational study on both WH₆ and WF₆ using a relativistic pseudopotential on tungsten, comparing results at the HF and MP2 levels with density functional calculations using local (SVWN), nonlocal (BLYP), and hybrid HF-DFT (ACM) functionals. In agreement with the earlier all-electron HF study of Schaefer and co-workers (J. Chem. Phys. 1993, 98, 508), we find that the ground state geometry of WH₆ is far from octahedral; instead, there are four low-lying structures of C_3v (2) and C_5v (2) symmetry. Barrier heights for interconversion of these isomers are low, indicating a highly fluxional molecule. In contrast, the octahedral structure appears to be the only stable species on the ground state potential energy surface of WF₆. It derives its stability from the greater ionic character of the W?F bond compared to that of W?H.