Double hybrid density-functional theory using the coulomb-attenuating method.

A double hybrid approximation using the Coulomb-attenuating method (CAM-DH) is derived within range-separated density-functional perturbation theory, in the spirit of a recent work by Cornaton et al. (Phys. Rev. A 2013, 88, 022516). The energy expression recovered through second order is linear in the parameters α and β that control the Coulomb attenuation. The method has been tested within the local density approximation on a small test set consisting of rare-gas and alkaline-earth-metal dimers as well as diatomics with single, double, and triple bonds. In this context, the semiempirical α = 0.19 and β = 0.46 parameters, which were optimized for the hybrid CAM-B3LYP functional, do not provide accurate interaction and total energies. Using semilocal functionals with density scaling, which was neglected in this work, may lead to different conclusions. Calibration studies on a larger test set would be necessary at this point. This is left for future work. Finally, we propose as a perspective, an alternative CAM-DH approach that relies on the perturbation expansion of a partially long-range-interacting wavefunction. In this case, the energy is not linear anymore in α and β. Work is in progress in this direction. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]