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arxiv 2406.06883 v1 pith:SHRUKQYV submitted 2024-06-11 cond-mat.mtrl-sci physics.comp-ph

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

classification cond-mat.mtrl-sci physics.comp-ph
keywords chalcogenidescoppererrorhybrididentifymethodsresultunderestimation
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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Gap opening remains elusive in copper chalcogenides (Cu$_{2}X$, $X$ = 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 4$s$-3$d$ 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 Cu$_{2}X$, suggesting their predominantly electronic nature. Our work not only clarifies the debate about the Cu$_{2}X$ 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.

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