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Solid state physicists adopt a very different definition of strong correlations. Here, the reference system is the Kohn Sham Greens function  evaluated in some implementation of the density functional theory such as the LDA. Hence, for condensed matter scientists, by definition, a  strongly correlated material is one where $\Sigma - V_KS V_{KS}  $ is large at low energy. In quantum chemistry   Aron J Cohen, Paula Mori-Sánchez, Weitao Yang