Addendum to Free-energy functional of the Debye-Huckel model of simple fluids

In previous publications [arXiv:1608.08430, arXiv:1704.06502], the authors have proposed Debye-Huckel-approximate free-energy functionals of the pair distribution functions for one-component fluid and two-component plasmas. These functionals yield the corresponding Debye-Huckel integral equations when they are minimized with respect to the pair distribution functions, lead to correct thermodynamic relations and fulfill the virial theorem. In the present addendum, we update our results by providing simpler functionals that have the same properties. We relate these functionals to the approaches of Lado [Phys. Rev. A 8:2548, 1973] and of Olivares and McQuarrie [J. Chem. Phys. 65:3604, 1976]. We also discuss briefly the non-uniqueness issue that is raised by these results.