A comparison of geometric parameters from PBE-based doubly hybrid density functionals PBE0-DH, PBE0-2, and xDH-PBE0.

We present a systematic investigation on the optimized geometric parameters for covalently bonded molecules, nonbonded intermolecular complexes, and transition state structures from three PBE (Perdew-Burke-Ernzerhof)-based doubly hybrid (DH) density functionals, namely PBE0-DH, PBE0-2, and xDH-PBE0. While the former two are the B2PLYP-type of DH functionals with no fit parameters, the latter is the XYG3-type of DH functional (xDH for short) with three fit parameters, whose energy expression is constructed by using density and orbital information from another standard (general) Kohn-Sham functional (i.e., PBE0) for doing the self-consistent field calculations. Generally good performances have been obtained with all three DH functionals, in particular, with xDH-PBE0.