RT Journal Article
SR Electronic
T1 Understanding band gaps of solids in generalized Kohn–Sham theory
JF Proceedings of the National Academy of Sciences
JO Proc Natl Acad Sci USA
FD National Academy of Sciences
SP 2801
OP 2806
DO 10.1073/pnas.1621352114
VO 114
IS 11
A1 Perdew, John P.
A1 Yang, Weitao
A1 Burke, Kieron
A1 Yang, Zenghui
A1 Gross, Eberhard K. U.
A1 Scheffler, Matthias
A1 Scuseria, Gustavo E.
A1 Henderson, Thomas M.
A1 Zhang, Igor Ying
A1 Ruzsinszky, Adrienn
A1 Peng, Haowei
A1 Sun, Jianwei
A1 Trushin, Egor
A1 Görling, Andreas
YR 2017
UL http://www.pnas.org/content/114/11/2801.abstract
AB Semiconductors and insulators have a fundamental energy gap and absorb light at a continuum of photon energies above this gap. They also have a band structure of one-electron energies, and a band gap separating unoccupied from occupied one-electron states. When should these gaps be equal? It is known that they are not equal in the exact Kohn–Sham density-functional theory but are equal in commonly used density-functional approximations, such as the generalized gradient approximation (GGA). We show here that they are also equal (and improved) in higher level approximations, such as the meta-GGA or the hybrid of GGA with exact exchange, when the effective one-electron potential is not constrained to be a multiplication operator.The fundamental energy gap of a periodic solid distinguishes insulators from metals and characterizes low-energy single-electron excitations. However, the gap in the band structure of the exact multiplicative Kohn–Sham (KS) potential substantially underestimates the fundamental gap, a major limitation of KS density-functional theory. Here, we give a simple proof of a theorem: In generalized KS theory (GKS), the band gap of an extended system equals the fundamental gap for the approximate functional if the GKS potential operator is continuous and the density change is delocalized when an electron or hole is added. Our theorem explains how GKS band gaps from metageneralized gradient approximations (meta-GGAs) and hybrid functionals can be more realistic than those from GGAs or even from the exact KS potential. The theorem also follows from earlier work. The band edges in the GKS one-electron spectrum are also related to measurable energies. A linear chain of hydrogen molecules, solid aluminum arsenide, and solid argon provide numerical illustrations.