title: Systematic investigation on topological properties of layered GaS and GaSe under strain.
abstract: The topological properties of layered β-GaS and ε-GaSe under strain are systematically investigated by ab initio calculations with the electronic exchange-correlation interactions treated beyond the generalized gradient approximation (GGA). Based on the GW method and the Tran-Blaha modified Becke-Johnson potential approach, we find that while ε-GaSe can be strain-engineered to become a topological insulator, β-GaS remains a trivial one even under strong strain, which is different from the prediction based on GGA. The reliability of the fixed volume assumption rooted in nearly all the previous calculations is discussed. By comparing to strain calculations with optimized inter-layer distance, we find that the fixed volume assumption is qualitatively valid for β-GaS and ε-GaSe, but there are quantitative differences between the results from the fixed volume treatment and those from more realistic treatments. This work indicates that it is risky to use theoretical approaches like GGA that suffer from the band gap problem to address physical properties, including, in particular, the topological nature of band structures, for which the band gap plays a crucial role. In the latter case, careful calibration against more reliable methods like the GW approach is strongly recommended.
authors.affiliation: School of Physics, Peking University, Beijing 100871, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: An
authors.affiliation: Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People's Republic of China.
authors.forename: Feng
authors.initials: F
authors.lastname: Wu
authors.affiliation: Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People's Republic of China.
authors.forename: Hong
authors.initials: H
authors.lastname: Jiang
authors.affiliation: School of Physics, Peking University, Beijing 100871, People's Republic of China.
authors.forename: Guang-Shan
authors.initials: GS
authors.lastname: Tian
authors.affiliation: School of Physics, Peking University, Beijing 100871, People's Republic of China.
authors.forename: Xin-Zheng
authors.initials: XZ
authors.lastname: Li