First-principles study on the conventional superconductivity of N-doped fcc-LuH_(3)

Recently,room-temperature superconductivity has been reported in a nitrogen-doped lutetium hydride at near-ambient pressure[Dasenbrock-Gammon et al.,Nature 615,244(2023)].The superconducting properties might arise from Fm3m-LuH_(3)−δNε.Here,we systematically study the phase diagram of Lu–N–H at 1 GPa using first-principles calculations,and we do not find any thermodynamically stable ternary compounds.In addition,we calculate the dynamic stability and superconducting properties of N-doped Fm3m-LuH_(3) using the virtual crystal approximation(VCA)and the supercell method.The R3m-Lu_(2)H_(5)N predicted using the supercell method could be dynamically stable at 50 GPa,with a T_(c) of 27 K.According to the VCA method,the highest T_(c) is 22 K,obtained with 1%N-doping at 30 GPa.Moreover,the doping of nitrogen atoms into Fm3m-LuH_(3) slightly enhances T_(c),but raises the dynamically stable pressure.Our theoretical results show that the T_(c) values of N-doped LuH_(3) estimated using the Allen–Dynes-modified McMillan equation are much lower than room temperature.

A fresh class of superconducting and hard pentaborides

On the basis of the current theoretical understanding of boron-based hard superconductors under ambient conditions,numerous studies have been conducted with the aim of developing superconducting materials with favorable mechanical properties using boron-rich compounds.In this paper,first-principles calculations reveal the existence of an unprecedented family of tetragonal pentaborides MB_(5)(M=Na,K,Rb,Ca,Sr,Ba,Sc,and Y),comprising B_(20)cages and centered metal atoms acting as stabilizers and electron donors to the boron sublattice.These compounds exhibit both superconductivity and high hardness,with the maximum superconducting transition temperature T_(c)of 18.6 K being achieved in RbB5 and the peak Vickers hardness Hv of 35.1 GPa being achieved in KB_(5)at 1 atm.The combination of these properties is particularly evident in KB_(5),RbB5,and BaB5,with Tc values of∼14.7,18.6,and 16.3 K and H_(v)values of∼35.1,32.4,and 33.8 GPa,respectively.The results presented here reveal that pentaborides can provide a framework for exploring and designing novel superconducting materials with favorable hardness at achievable pressures and even under ambient conditions.

Structural and electrical properties of Ga–Te systems under high pressure

First-principles evolutionary calculation was performed to search for all probable stable Ga–Te compounds at extreme pressure. In addition to the well-known structures of P6_3/mmc and Fm-3 m Ga Te and I4/m Ga_2 Te_5, several new structures were uncovered at high pressure, namely, orthorhombic I4/mmm GaTe_2 and monoclinic C2/m Ga Te_3, and all the Ga–Te structures stabilize up to a maximum pressure of 80 GPa. The calculation of the electronic energy band indicated that the high-pressure phases of the Ga–Te system are metallic, whereas the low-pressure phases are semiconductors. The electronic localization functions(ELFs) of the Ga–Te system were also calculated to explore the bond characteristics. The results showed that a covalent bond is formed at low pressure, however, this bond disappears at high pressure, and an ionic bond is formed at extreme pressure.

Variational and diffusion Monte Carlo simulations of a hydrogen molecular ion in a spherical box

The variational and diffusion Monte Carlo approaches are used to study the ground-state properties of a hydrogen molecular ion in a spheroidal box. In this work, we successfully treat the zero-point motion of protons in the same formalism with as of electrons and avoid the Born–Oppenheimer approximation in density function theory. The study shows that the total energy increases with the decrease in volume, and that the distance between protons decreases as the pressure increases.Considering the motion of protons, the kinetic energy of the electron is higher than that of the fixed model under the same conditions and increases by 5%. The kinetic energy of the proton is found to be small under high pressure, which is only a fraction of the kinetic energy of the electron.

Structural and Electrical Properties of Be(x)Zn_(1-x)O Alloys under High Pressure

We conduct extensive research into the structures of Be_(x)Zn_(1-x)OO ternary alloys in a pressure range of 0-60GPa,using the ab initio total energy evolutionary algorithm and total energy calculations,finding several metastable structures.Our pressure-composition phase diagram is constructed using the enthalpy results.In addition,we calculate the electronic structures of the Be_(x)Zn_(1-x)OO structures and investigate the bandgap values at varying pressures and Be content.The calculated results show that the bandgap of the Be_(x)Zn_(1-x)OO ternary alloys increases with an increase in Be content at the same pressure.Moreover,the bandgap of the Be_(x)Zn_(1-x)OO ternary alloys increases with the increasing pressure with fixed Be content.At the same Be content,the formation enthalpy of the Be_(x)Zn_(1-x)OO ternary alloys first decreases,then increases with the increasing pressure.

Ab initio studies on ammonium iodine under high pressure

Ammonium iodine(NH4I)as an important member of hydrogen-rich compounds has attracted a great deal of attention owing to its interesting structural changes triggered by the relative orientations of adjacent ammonium ions.Previous studies of ammonium iodide have remained in the low pressure range experimentally,which we first extended to so high pressure(250 GPa).We have investigated the structures of ammonium iodine under high pressure through ab initio evolutionary algorithm and total energy calculations based on density functional theory.The static enthalpy calculations show that phase V is stable until 85 GPa where a new phase Ibam is identified.Calculations of phonon spectra show that the Ibam phase is stable between 85 GPa and 101 GPa and the Cm phase is stable up to 130 GPa.In addition,ammonium iodine dissociates into NH3,H2,and I2 at 74 GPa.Subsequently,we analyzed phonon spectra and electronic band structures,finding that phonon softening is not the reason of dissociation and NH4I is always a semiconductor within the pressure range.

Resistive switching and artificial synaptic performances of memristor based on low-dimensional bismuth halide perovskites

Zero-dimensional(0D)-Cs_(3)Bi_(2)I_(9),two-dimensional(2D)-Cs_(3)Bi_(2)Br_(9),and one-dimensional(1D)-Cs3Bi2Cl9 perovskite films have been successfully grown on indium tin oxide(ITO)glass substrates,which were used to fabricate memristors with the structure of Al/Cs_(3)Bi_(2)X_(9)(X=I,Br,and Cl)/ITO glass.The current three types of memristors exhibited bipolar resistive switching behaviors.Both the endurance and retention time tests clearly demonstrated the excellent stability of present devices.Especially,the ON/OFF ratio of the 0D-Cs_(3)Bi_(2)I_(9)device is close to 104 at the reading voltage of 0.1 V,which is nearly 100 and 1000 times larger than those of the 1D-Cs3Bi2Cl9 device and the 2D-Cs_(3)Bi_(2)Br_(9)device,respectively.The activation energy of halide vacancies in the Cs_(3)Bi_(2)X_(9)(X=I,Br,and Cl)films was calculated using the density functional theory by considering a minimum migration path,demonstrating the dimensionality of the Cs_(3)Bi_(2)X_(9)(X=I,Br,and Cl)film affected the formation and rupture of conductive filaments.Moreover,the short-term plasticity and long-term plasticity of biological synapse were simulated by evaluating the conductance responses of Al/Cs_(3)Bi_(2)X_(9)(X=I,Br,and Cl)/ITO devices under various voltage pulses in detail.The duration time of long-term plasticity in all the present devices can last for up to 250 s.The 0D-Cs_(3)Bi_(2)I_(9)device showed both the highest spikeduration-dependent plasticity and paired-pulse facilitation indexes compared to the other two devices.Additionally,the 0DCs_(3)Bi_(2)I_(9)device successfully established the associative learning behavior by simulating the Pavlov’s dog experiment.

Electrically manipulating magnetization reversal via energy band engineering

Realization of a magnetization reversal by an external electric field is vital for developing ultra-low-power spintronic devices.In this report,starting from energy band engineering,a general design principle is proposed for achieving electrical manipulation of a nonvolatile 180°magnetization reversal.A half semiconductor(HSC)and a bipolar magnetic semiconductor(BMS)are selected as the model of magnetic layers,whose conduction-band minimum and valence-band maximum are in the same and opposite spin states,respectively.Based on the analysis of virtual hopping and tight-binding models,the interlayer coupling of HSC/insulator/BMS devices is successfully tuned between ferromagnetic and antiferromagnetic interactions by varying electric field directions.Moreover,the interlayer coupling nearly disappears after removing the electric field,proving the nonvolatile magnetization reversal.Using first-principles calculations,the feasibility of present design strategy is further confirmed by a representative device with the structure of CrBr3/h-BN/2H-VSe_(2).This design guideline and physical phenomena may open an avenue to explore magnetoelectric coupling mechanisms and develop next-generation spintronic devices.

Ternary superconducting cophosphorus hydrides stabilized via lithium

Inspired by the diverse properties of sulfur hydrides and phosphorus hydrides,we combine first-principles calculations with structure prediction to search for stable structures of Li−P−H ternary compounds at high pressures with the aim of finding novel superconductors.It is found that phosphorus hydrides can be stabilized under pressure via additional doped lithium.