The Kohn–Sham auxiliary system
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Density functional theory is the most widely used method today for electronic structure calculations because of the approach proposed by Kohn and Sham in 1965: to replace the original many-body problem by an auxiliary independent-particle problem. This is an ansatz1 that, in principle, leads to exact calculations of properties of many-body systems using independent-particle methods; in practice, it has made possible approximate formulations that have proved to be remarkably successful. As a self-consistent method, the Kohn–Sham approach involves independent particles but an interacting density, an appreciation of which clarifies the way the method ...