Theoretical mixing coefficients for hybrid functionals

The theoretical foundations of the double hybrid exchange-correlation functionals have been recently analyzed by Sharkas [J. Chem. Phys. 134, 064113 (2011)10.1063/1.3544215] and, successively, by Brmond and Adamo [J. Chem. Phys. 135, 024106 (2011)10.1063/1.3604569] and by Toulouse [J. Chem. Phys. 135, 101102 (2011)10.1063/1.3640019]. This analysis partially resulted in the introduction of a new class of double hybrids depending on just one parameter, the value of which was assumed to be 0.5 by Brmond and Adamo. In this note, I will suggest that other values can be chosen and that all these choices can be justified using the same theoretical arguments. These values are also theoretical mixing coefficients for single-hybrids, i.e., functional where only the exchange is hybridized. © 2012 American Institute of Physics.