Bipolarons in a KCl melt

A theory of two excess electrons in alkali halide melts is developed using variational estimates of path integrals. As a result of the strong screenin g, the average field generated by the ions has little influence on the elec trons and the problem reduces to a study of a bipolaron type of free energy functional. The behavior of this functional is determined as a function of the thermodynamic and structural characteristics of the melt. Variational bipolaron calculations are made using the approximation of uncorrelated ele ctrons and using Kohn-Sham theory to allow for electron-electron correlatio ns. The results of the calculations using Kohn-Sham theory agree with the d ata obtained by quantum molecular dynamics and show that a correct choice o f trial wave function which allows explicitly for the correlation of two el ectrons is required to obtain a correct estimate of bipolaron stability. (C ) 2000 MAIK "Nauka/ Interperiodica".