Structure and bonding of F2O2

The geometry of F2O2 is determined by several ab initio methods, including Moller--Plesset perturbation theory (MP) based on an RHF reference and externally contracted configuration interaction (CCI) based on a complete-active-space (CAS) reference. Basis sets with polarization and diffuse functions are used. Compared to the gas-phase experimental structure, SCF and MP bond lengths are very poor, and the MP geometries vary considerably with basis set changes. Three sizes of CAS are examined and each results in a dissociative surface. Only CCI calculations from a large CAS produce a geometry in reasonable agreement with experiment. After addition of Davidson's correction, the remaining errors in the O--O and O--F bond lengths are 0.016 and 0.025 A, respectively