A way to identify whether a DFT gap is from right reasons or error cancellations: The case of copper chalcogenides

Author:

Shen Jiale1ORCID,Liu Haitao23ORCID,Li Yuanchang1ORCID

Affiliation:

1. Key Lab of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), and Advanced Research Institute of Multidisciplinary Science, Beijing Institute of Technology 1 , Beijing 100081, China

2. Institute of Applied Physics and Computational Mathematics 2 , Beijing 100088, China

3. National Key Laboratory of Computational Physics 3 , Beijing 100088, China

Abstract

Gap opening remains elusive in copper chalcogenides (Cu2X, X = S, Se, and Te), not least because Hubbard + U, hybrid functional, and GW methods have also failed. In this work, we elucidate that their failure originates from a severe underestimation of the 4s–3d orbital splitting of the Cu atom, which leads to a band-order inversion in the presence of an anionic crystal field. As a result, the Fermi energy is pinned due to symmetry, yielding an invariant zero gap. Utilizing the hybrid pseudopotentials to correct the underestimation on the atomic side opens up gaps of experimental magnitude in Cu2X, suggesting their predominantly electronic nature. Our work not only clarifies the debate about the Cu2X gap but also provides a way to identify which of the different methods really captures the physical essence and which is the result of error cancellation.

Funder

Ministry of Science and Technology of the People’s Republic of China

National Natural Science Foundation of China

Publisher

AIP Publishing

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