First-principles Study On 3dTMP₄?TM=V,Cr,Mn,Fe? And Be_xS_y

Transition-metal phosphides possess outstanding physical and chemical properties,so they attract increasing attentions on the applications for energy conversion and storage.Therefore,we perform the investigations of the structural,electronic and elastic properties for 3d TMP₄?TM=V,Cr,Mn and Fe?using First-principles calculations.First,3d TMP₄ are featured with alternating phosphorus sheets with ten-numbered phosphorus rings and varied transition-metal layers.Secondly,hybrid DFT calculations reveal that 3d TMP₄ ranging from metallic behavior for VP₄,semiconducting CrP₄ with the narrow direct band gap of0.63 eV,to enlarged semiconducting MnP₄ and FeP₄ with band gap of 1.6-2.1 eV,as the atomic number increases.Thirdly,the Valence electron density distribution and Crystal Orbital Hamiltonian Population?COHP?analysis indicates that P-P and TM-P covalent interactions are dominated,which are responsible for the structural and electronic stability.Light-metal sulfides have attracted great attention due to the application to energy storage devices.We combined first-principles calculations with structure searching,explored stable binary compounds systematacially in Be-S system.Interestingly,our results identify some stable Be_xS_y phases in bulk and two-dimensional configurations.BeS₂ in bulk adopts P???structure at ambient pressure,C2 phase over 1.6 GPa and then a cubic c-BeS₂with unique S₂ dimers up to 5.8 GPa,c-BeS₂ stable thermodynamically at 25GPa.We also present a monolayer penta-BeS₂ with Be₂S₃ pentagons,and a bilayer T-BeS structure where the single layer is similar to h-BN.Hybrid DFT calculations reveal that P???-BeS₂ and c-BeS₂are direct semiconductors,the band gaps are 3.38 eV and 2.53 eV respectively.C2-BeS₂,penta-BeS₂ and T-BeS are indirect semiconductors,the band gaps are 2.02 eV,3.79 eV and2.53 eV respectively.The Electron Localization Function?ELF?and COHP analysis indicates that S-S shows strong covalent bond character,Be-S bonds hold ionic property mainly with some covalent feature,which plays a key role for the structural stability.