Communication: Rationale for a new class of double-hybrid approximations in density-functional theory

We provide a rationale for a new class of double-hybrid approximations introduced by Bremond and Adamo [J. Chem. Phys. 135, 024106 (2011)] which combine an exchange-correlation density functional with Hartree-Fock exchange weighted by lambda and second-order Moller-Plesset (MP2) correlation weighted by lambda(3). We show that this double-hybrid model can be understood in the context of the density-scaled double-hybrid model proposed by Sharkas et al. [J. Chem. Phys. 134, 064113 (2011)], as approximating the density-scaled correlation functional E(c)[n(1/lambda)] by a linear function of lambda, interpolating between MP2 at lambda = 0 and a density-functional approximation at lambda = 1. Numerical results obtained with the Perdew-Burke-Ernzerhof density functional confirms the relevance of this double-hybrid model. (C) 2011 American Institute of Physics. [doi:10.1063/1.3640019]