  Without the use of any empirical fitting to experimental or high-level ab
initio data, we present a double-hybrid density functional approximation for
the exchange-correlation energy, combining the exact Hartree-Fock exchange and
second-order Moller-Plesset (MP2) correlation with the Perdew-Burke-Ernzerhof
(PBE) functional. This functional, denoted as PBE0-2, is shown to be accurate
for a wide range of applications, when compared with other functionals and the
ab initio MP2 method. The qualitative failures of conventional density
functional approximations, such as self-interaction error and noncovalent
interaction error, are significantly reduced by PBE0-2.
