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".