= Walter Kohn
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<Walter Kohn> and <Pierre Hohenberg> established a foundation for <density functional theory>: under their ground-state assumptions, the <electron density> determines the external scalar potential up to an additive constant. They formulated the ground-state <energy> as a universal density functional plus the external-potential contribution, with a <variational principle> selecting the physical density. This replaces the full many-electron <wave function> as the basic variable by a function of only three spatial coordinates. The theorem establishes the framework, rather than providing an explicit exact functional for practical computation.<Inhomogeneous electron gas by Pierre Hohenberg and Walter Kohn>[Physical Review 136, B864 (1964), density-potential uniqueness and variational principle]{ref}
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{title=Portrait of <Walter Kohn>}
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