In this work,we focus on the structural and electronic properties of lanthanum mono-nitride s under high pressure.Based on firstprinciples calculations and crystal structure predictions,we identified an anti-ferroelec...In this work,we focus on the structural and electronic properties of lanthanum mono-nitride s under high pressure.Based on firstprinciples calculations and crystal structure predictions,we identified an anti-ferroelectric orthogonal phase with space group Pbcm.It is predicted to be thermodynamically stable from 20 to 60 GPa,above which the tetragonal phase without the antiferroelectric distortion will substitute it.However,the anti-ferroelectric distortion can be enhancedby reducing the pressure,and a phase transition to a NiAs-type(B8,P63/mmc) structure occurs at about 20 GPa.The calculated double-well potential for La atoms along the c direction in the B8 phase reveals that it should exhibit ferroelectric properties at low temperatures.Enthalpy calculations well confirm their phase transition sequences under high pressure.Electtonic properties calculations suggest that all the newly identified phases are semiconductors and the corresponding structural distortions can increase their bandgaps.When increasing the pressure to 50 GPa,the tetragonal phase undergoes a semiconductor-to-semimetal transition.Taking the spin-orbit coupling into account,the semimetal phase becomes a topological insulator with a small bandgap.Finally,given the similarities between the ionic compounds LaN and BaO,we predict that the most stable phase for BaO at about 25 GPa should also be the anti-ferroelectric orthogonal phase instead of the tetragonal phase.展开更多
In recent decades,pentazolate salts have gained considerable attention as high energy density materials(HEDMs).Using the machine-learning accelerated structure searching method,we predicted four pentazolate salts stab...In recent decades,pentazolate salts have gained considerable attention as high energy density materials(HEDMs).Using the machine-learning accelerated structure searching method,we predicted four pentazolate salts stabilized with tetravalent metals(Ti-N and Zr-N).Specifically,the ground state MN_(20)(M=Ti,Zr)adopts the space-group P 4/mcc under ambient conditions,transforming into the I-4 phase at higher pressure.Moreover,the I-4-MN_(20)becomes energetically stable at moderate pressure(46.8 GPa for TiN_(20),38.7 GPa for ZrN_(20)).Anharmonic phonon spectrum calculations demonstrate the dynamic stabilities of these MN_(20)phases.Among them,the P 4/mcc phase can be quenched to 0 GPa.Further ab-initio molecular dynamic simulations suggest that the N_(5)rings within these MN_(20)systems can still maintain integrity at finite temperatures.Calculations of the projected crystal orbital Hamilton population and reduced density gradient revealed their covalent and noncovalent interactions,respectively.The aromaticity of the N_(5)ring was investigated by molecular orbital theory.Finally,we predicted that these MN_(20)compounds have very high energy densities and exhibit good detonation velocities and pressures,compared to the HMX explosive.These calculations enrich the family of pentazolate compounds and may also guide future experiments.展开更多
In this paper, we study the growth of the solutions for 1st kind of differential equations of higher order in the unit disc. We give a sufficient condition for all solutions of second order linear differential equatio...In this paper, we study the growth of the solutions for 1st kind of differential equations of higher order in the unit disc. We give a sufficient condition for all solutions of second order linear differential equation to be inadmissible and a sufficient condition for all solutions of higher order linear differential equation to be of infinite order.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 12125404, 11974162, and 11834006)the Fundamental Research Funds for the Central Universities。
文摘In this work,we focus on the structural and electronic properties of lanthanum mono-nitride s under high pressure.Based on firstprinciples calculations and crystal structure predictions,we identified an anti-ferroelectric orthogonal phase with space group Pbcm.It is predicted to be thermodynamically stable from 20 to 60 GPa,above which the tetragonal phase without the antiferroelectric distortion will substitute it.However,the anti-ferroelectric distortion can be enhancedby reducing the pressure,and a phase transition to a NiAs-type(B8,P63/mmc) structure occurs at about 20 GPa.The calculated double-well potential for La atoms along the c direction in the B8 phase reveals that it should exhibit ferroelectric properties at low temperatures.Enthalpy calculations well confirm their phase transition sequences under high pressure.Electtonic properties calculations suggest that all the newly identified phases are semiconductors and the corresponding structural distortions can increase their bandgaps.When increasing the pressure to 50 GPa,the tetragonal phase undergoes a semiconductor-to-semimetal transition.Taking the spin-orbit coupling into account,the semimetal phase becomes a topological insulator with a small bandgap.Finally,given the similarities between the ionic compounds LaN and BaO,we predict that the most stable phase for BaO at about 25 GPa should also be the anti-ferroelectric orthogonal phase instead of the tetragonal phase.
基金J.S.gratefully acknowledges the financial support from the National Natural Science Foundation of China(12125404,11974162,11834006)the Fundamental Research Funds for the Central Universities.K.X.acknowledges the National Natural Science Foundation of China under 12004185+2 种基金the Natural Science Foundation of the Jiangsu Higher Education Institutions of China under 20KJB140016the Scientific Research Start-up Funds of Nanjing Forestry University(163101110)the financial support from the Project funded by China Postdoctoral Science Foundation(2019M651767).
文摘In recent decades,pentazolate salts have gained considerable attention as high energy density materials(HEDMs).Using the machine-learning accelerated structure searching method,we predicted four pentazolate salts stabilized with tetravalent metals(Ti-N and Zr-N).Specifically,the ground state MN_(20)(M=Ti,Zr)adopts the space-group P 4/mcc under ambient conditions,transforming into the I-4 phase at higher pressure.Moreover,the I-4-MN_(20)becomes energetically stable at moderate pressure(46.8 GPa for TiN_(20),38.7 GPa for ZrN_(20)).Anharmonic phonon spectrum calculations demonstrate the dynamic stabilities of these MN_(20)phases.Among them,the P 4/mcc phase can be quenched to 0 GPa.Further ab-initio molecular dynamic simulations suggest that the N_(5)rings within these MN_(20)systems can still maintain integrity at finite temperatures.Calculations of the projected crystal orbital Hamilton population and reduced density gradient revealed their covalent and noncovalent interactions,respectively.The aromaticity of the N_(5)ring was investigated by molecular orbital theory.Finally,we predicted that these MN_(20)compounds have very high energy densities and exhibit good detonation velocities and pressures,compared to the HMX explosive.These calculations enrich the family of pentazolate compounds and may also guide future experiments.
文摘In this paper, we study the growth of the solutions for 1st kind of differential equations of higher order in the unit disc. We give a sufficient condition for all solutions of second order linear differential equation to be inadmissible and a sufficient condition for all solutions of higher order linear differential equation to be of infinite order.
