Groundstate KohnSham density functional theory provides, in principle, the exact groundstate energy and electronic spin densities of real interacting electrons in a static external potential. In practice, the exact density functional for the exchangecorrelation (xc) energy must be approximated in a computationally efficient way. About 20 mathematical properties of the exact xc functional are known. In this work, we review and discuss these known constraints on the xc energy and hole. By analyzing a sequence of increasingly sophisticated density functional approximations (DFAs), we argue that ( a) the satisfaction of more exact constraints and appropriate norms makes a functional more predictive over the immense space of manyelectron systems and ( b) fitting to bonded systems yields an interpolative DFA that may not extrapolate well to systems unlike those in the fitting set. We discuss both how the class of welldescribed systems has grown along with constraint satisfaction and the possibilities for future functional development.
 Award ID(s):
 1939528
 NSFPAR ID:
 10326295
 Date Published:
 Journal Name:
 Science
 Volume:
 374
 Issue:
 6573
 ISSN:
 00368075
 Page Range / eLocation ID:
 1322 to 1323
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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