THEORY OF ELECTRONIC CORRELATIONS IN SOLIDS

A formalism is presented for the computation of long range as well as short range correlations in the electronic ground state of a solid. It is based on a Local Approach to the correlation problem which was successfully tested before for small molecules. The method connects two approaches to the correlation problem. One is that of the RPA which is often applied in solid state physics and describes the long range aspects of the correlated electronic motions. The other is that of quantum chemistry which tries to calculate to high accuracy the short range part of the correlation problem. The method is variational in nature. The approximations which have been made exclude the application of the present formalism to strongly correlated systems such as valence fluctuating systems. © 1979 Springer-Verlag.