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Calculation and interpretation of classical turning surfaces in solids

Kaplan, Aaron D.; Clark, Stewart J.; Burke, Kieron; Perdew, John P.

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Aaron D. Kaplan

Kieron Burke

John P. Perdew


Classical turning surfaces of Kohn–Sham potentials separate classically allowed regions (CARs) from classically forbidden regions (CFRs). They are useful for understanding many chemical properties of molecules but need not exist in solids, where the density never decays to zero. At equilibrium geometries, we find that CFRs are absent in perfect metals, rare in covalent semiconductors at equilibrium, but common in ionic and molecular crystals. In all materials, CFRs appear or grow as the internuclear distances are uniformly expanded. They can also appear at a monovacancy in a metal. Calculations with several approximate density functionals and codes confirm these behaviors. A classical picture of conduction suggests that CARs should be connected in metals, and disconnected in wide-gap insulators, and is confirmed in the limits of extreme compression and expansion. Surprisingly, many semiconductors have no CFR at equilibrium, a key finding for density functional construction. Nonetheless, a strong correlation with insulating behavior can still be inferred. Moreover, equilibrium bond lengths for all cases can be estimated from the bond type and the sum of the classical turning radii of the free atoms or ions.


Kaplan, A. D., Clark, S. J., Burke, K., & Perdew, J. P. (2021). Calculation and interpretation of classical turning surfaces in solids. npj Computational Materials, 7, Article 25.

Journal Article Type Article
Acceptance Date Dec 12, 2020
Online Publication Date Feb 1, 2021
Publication Date 2021
Deposit Date Jun 4, 2021
Publicly Available Date Jun 4, 2021
Journal npj Computational Materials
Publisher Nature Research
Peer Reviewed Peer Reviewed
Volume 7
Article Number 25


Published Journal Article (1.4 Mb)

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