The paper by A. S. Rodin, A. Carvalho, and A. H. Castro Neto investigates the strain-induced gap modification in black phosphorus using density functional theory (DFT) and tight-binding models. They determine the localized orbital composition of the individual bands from first-principles calculations and construct an effective low-energy Hamiltonian at the Γ point. The study shows that uniaxial stress applied perpendicular to the layer can change the gap size, leading to a semiconductor-metal transition. The authors also discuss the structural characteristics of black phosphorus, which is composed of flattened P$_4$ clusters linked together, forming a puckered structure. They use DFT to model strained layers and demonstrate that moderate compression can cause a semiconductor-metal transition, with the bandgap closing and the material transitioning from a direct to an indirect bandgap semiconductor, semimetal, and eventually a metal. The findings highlight the unique electronic and structural transformations in black phosphorus under strain, making it an interesting material for fundamental physics studies.The paper by A. S. Rodin, A. Carvalho, and A. H. Castro Neto investigates the strain-induced gap modification in black phosphorus using density functional theory (DFT) and tight-binding models. They determine the localized orbital composition of the individual bands from first-principles calculations and construct an effective low-energy Hamiltonian at the Γ point. The study shows that uniaxial stress applied perpendicular to the layer can change the gap size, leading to a semiconductor-metal transition. The authors also discuss the structural characteristics of black phosphorus, which is composed of flattened P$_4$ clusters linked together, forming a puckered structure. They use DFT to model strained layers and demonstrate that moderate compression can cause a semiconductor-metal transition, with the bandgap closing and the material transitioning from a direct to an indirect bandgap semiconductor, semimetal, and eventually a metal. The findings highlight the unique electronic and structural transformations in black phosphorus under strain, making it an interesting material for fundamental physics studies.