Predicting anomalous quantum confinement effect in van der Waals materials
Francesca Tavazza, Kamal Choudhary
Materials with van der Waals bonding are known to exhibit a quantum confinement effect, in which the electronic band gap of the three-dimensional realization of a material is lower than that of its two-dimensional (2D) counterpart. However, the possibility of an anomalous quantum confinement effect (AQCE) exists, where the band gap trend is reversed. In this work, we computationally identify materials for which such AQCE occurs. Using density-functional theory, we compute ∼1000 OptB88vdW (semilocal functional), ∼50 HSE06, and ∼50 PBE0 (hybrid functional) band gaps for bulk and their corresponding monolayers in the JARVIS-DFT database. OptB88vdW identifies 65 AQCE materials, but the hybrid functionals only confirm such findings in 14 cases. Some of the AQCE systems identified through HSE06 and PBE0 are hydroxides or oxide hydroxide compounds [ AlO H 2 , Mg ( OH ) 2 , Mg 2 H 2 O 3 , Ni ( OH ) 2 , and Sr H 2 O 3 ], as well as Sb-halogen-chalcogenide compounds (SbSBr and SbSeI) and alkali-chalcogenides (RbLiS and RbLiSe). A detailed electronic structure analysis, based on band structure and projected density of states, shows AQCE is often characterized by lowering of the conduction band in the monolayer and corresponding changes in the p z electronic orbital contribution, with z being the nonperiodic direction in the 2D case. We investigated the possibility of these materials being topological through spin-orbit spillage calculations and determined that they are not. We believe our computational results would spur the effort to validate the results experimentally and will have an impact on band-gap engineering applications based on low-dimensional materials. Our systematic approach also shows that data-driven approaches can be used to discover a new phenomenon such as AQCE.
and Choudhary, K.
Predicting anomalous quantum confinement effect in van der Waals materials, Physical Review Materials, [online], https://doi.org/10.1103/PhysRevMaterials.5.054602
(Accessed September 28, 2023)