Some Exact Conditions Satisfied by all Electronic Systems

SOME EXACT CONDITIONS SATISFIED BY ALL ELECTRONIC SYSTEMS 

In this section, we discuss some of the many exact conditions that can be shown to be satisfied by all interacting electronic systems in their ground states. We look at both real space and momentum space decompositions of the exchange-correlation energy. In the following sections, we show how knowledge of these exact conditions has been vital to the construction and testing of approximate density functionals. 

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