Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 144, Issue 8, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.4942016
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Funding
- National Science Foundation [DMR-0812195]
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We visualize the Kohn-Sham kinetic energy density (KED) and the ingredients - the electron density, its gradient, and Laplacian - used to construct orbital-free models of it, for the AE6 test set of molecules. These are compared to related quantities used in metaGGA's, to characterize two important limits - the gradient expansion and the localized-electron limit typified by the covalent bond. We find the second-order gradient expansion of the KED to be a surprisingly successful predictor of the exact KED, particularly at low densities where this approximation fails for exchange. This contradicts the conjointness conjecture that the optimal enhancement factors for orbital-free kinetic and exchange energy functionals are closely similar in form. In addition we find significant problems with a recent metaGGA-level orbital-free KED, especially for regions of strong electron localization. We define an orbital-free description of electron localization and a revised metaGGA that improves upon atomization energies significantly. (C) 2016 AIP Publishing LLC.
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