Density functional Gaussian-type orbital approach in theoretical study of S2F2 isomerization

The structures of two isomers, difluorodisulfane (FSSF) and thiothionylfluoride (SSF2), and the corresponding transition structure were generated with density functional theory (DFT) methods. Three groups of DFT methods were used: local (Local Spin Density Approximation, LSDA), nonlocal (local with gradient corrections; BLYP and BP86), and hybrid methods that include a mixture of Hartree-Fock (HF) exchange with nonlocal correlation (Becke3BLYP, Becke3P86). An extended basis set [6-311++G(3df)] was used for all calculations, although satisfactory results can be obtained with the 6-311G(d) basis set. The geometries obtained were compared with both restricted Hartree-Fock (RHF) calculated and experimentally obtained-values. The energy outcome and the activation barrier for the isomerization were evaluated. It was determined that excellent geometries can be obtained with the Becke3B86 hybrid method, whereas for reasonable energies MP2 single-point calculations on these geometries are necessary. (C) 1996 by John Wiley & Sons, Inc.