It is shown that the Coulomb energy U of fully ionized ionic mixture can be written as a sum over partial contributions over ion species j: U= T Σ_j N_j u(Γ_j, y_j) (generalized linear mixing rule). In contrast to the traditional linear mixing rule, applicable for strong coupling, the partial contribution function u depends not only on Γ_j, but on an additional parameter y_j=(r_D/r_D^OCP)² also. Here r_D and r_D^OCP are Debye radii at the mixture and at one component plasma with coupling parameter Γ_j, correspondingly. The parameter y_j does not depend on a specific composition of the mixture, but on the Debye radius r_D only, making the function u(Γ_j, y_j) universal. The generalized linear mixing rule can be applied at any coupling parameter, if ionic mixture is not crystallized. It reproduces the results of Debye-Hückel theory at weak coupling and traditional linear mixing rule at strong coupling. It can be easily applied to the complicated mixtures, composed of a large number of ion species. Since y_j is temperature independent, the Coulomb contribution to Helmholtz free energy of the mixture can also be presented in a form of generalized linear mixing rule.

Page created on September 16, 2011.