The electronic band structures, densities of states （DOSs）, and projected densities of states （PDOSs） of the wurtzite In1-xGaxN with x=0, 0.0625, 0.125 are studied using the generalized-gradient approximation （GG...The electronic band structures, densities of states （DOSs）, and projected densities of states （PDOSs） of the wurtzite In1-xGaxN with x=0, 0.0625, 0.125 are studied using the generalized-gradient approximation （GGA） and GGA＋U in density functional theory. Our calculations suggest that in the case of wurtzite InN it is important to apply an on-site Hubbard correction to both the d states of indium and the p states of nitrogen in order to recover the correct energy level symmetry and obtain a reliable description of the InN band structure. The method is used to study the electronic properties of the wurtzite In1-xGaxN. The conduction band minimum （CBM） energy increases, while the valence band maximum （VBM） energy decreases with the increase of the gallium concentration. The effect leads to broadening the band gap （BG） and the valence band width （VBW）. Furthermore, the compressive strain in the crystal can cause the BG and the VBW to increase with the increase of gallium concentrations.展开更多
Calculating the impact of point defects on the macroscopic properties of technologically relevantsemiconductors remains a considerable challenge. Semi-empirical approaches, such as the tightbindingmethod, are very eff...Calculating the impact of point defects on the macroscopic properties of technologically relevantsemiconductors remains a considerable challenge. Semi-empirical approaches, such as the tightbindingmethod, are very efficient in calculating the electronic structure of large supercells containingone or several defects. However, the accuracy of these calculations depends on the quality of theparameters. Obtaining reliable parameters by fitting to the large number of entangled bands indefective supercells is a demanding task.We therefore present an alternative way by fitting to the atomand orbital projected densities of states. Starting with a tight-binding fit of the pristine material,we onlyneed a few physically motivated parameters for the fitting of defects. The training is done on data setsgenerated purely with parameter variations of tight-binding Hamiltonians. We demonstrate theefficiency of our approach for the calculation of the carbon monomer and the carbon dimersubstitutions in hexagonal boron nitride. The method opens a path towards understandingcomplicated defect landscapes using a computationally affordable semi-empirical approach withoutsacrificing accuracy.展开更多
First-principles calculations are carried out to examine the adsorption of acetylene over the Pd(111)surface.A hydrogen adsorption system is initially investigated to confirm the reliability of the selected calculatio...First-principles calculations are carried out to examine the adsorption of acetylene over the Pd(111)surface.A hydrogen adsorption system is initially investigated to confirm the reliability of the selected calculation method.Adsorption energies,Mulliken-populations,overlap populations,charge density,and projected density of states(PDOS)are then calculated in the optimised acetylene adsorption system.Results show that C_(2)H_(2) molecule tends to adsorb through the threefold parallel-bridge configuration that is computed to be the most stable.In this structure,the distance of the C-H bond is calculated to be 1.09 Å,and the C-C-H bond angle is 128°.The distance of the C-C bond in acetylene is 1.36 Å,increasing from 1.21 Å in the gas phase.Moreover,the C-C bond overlap population decreases from 1.98 to 1.38,revealing that the carbon configuration in C2H2 rehybridises from sp to sp^(2) and beyond.The obtained results are compared with available experimental studies on acetylene hydrogenation on single-metal surfaces.The PDOS study indicates that a carbonaceous layer may generate on the metal surface during acetylene adsorption.The carbonaceous layer can affect the adsorption and reaction of acetylene,thereby inactivating the metal surface.Our experiments also show that Pd exhibits high catalytic activity.展开更多
The density functional theory(DFT)combining with the non-equilibrium Green functions(NEGF)method is applied to the study of the electronic transport properties for a Di-thiol-benzene(DTB)molecule coupled to two Au(111...The density functional theory(DFT)combining with the non-equilibrium Green functions(NEGF)method is applied to the study of the electronic transport properties for a Di-thiol-benzene(DTB)molecule coupled to two Au(111)surfaces.The dependence of the transport properties on the bias,the coupling geometry of the molecule-electrode interface,and the intermolecular interaction are examined in detail.The results show that the existence of the hydrogen atom at the end of the DTB molecule would significantly decrease the transmission coefficients,and then the differential conductance(dI/dV).By changing the position of the DTB molecule located between two electrodes a maximum value of calculated current is observed.It is also found that the intermolecular interaction will strongly influence the transport properties of the system studied.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.50971094)the Natural Science Foundation of Beijing,China(Grant Nos.KZ201310028032 and 1092007)the Domestic Visiting Program for the Graduate Students of Inner Mongolia University,China
文摘The electronic band structures, densities of states （DOSs）, and projected densities of states （PDOSs） of the wurtzite In1-xGaxN with x=0, 0.0625, 0.125 are studied using the generalized-gradient approximation （GGA） and GGA＋U in density functional theory. Our calculations suggest that in the case of wurtzite InN it is important to apply an on-site Hubbard correction to both the d states of indium and the p states of nitrogen in order to recover the correct energy level symmetry and obtain a reliable description of the InN band structure. The method is used to study the electronic properties of the wurtzite In1-xGaxN. The conduction band minimum （CBM） energy increases, while the valence band maximum （VBM） energy decreases with the increase of the gallium concentration. The effect leads to broadening the band gap （BG） and the valence band width （VBW）. Furthermore, the compressive strain in the crystal can cause the BG and the VBW to increase with the increase of gallium concentrations.
基金funded by the Luxembourg National Research Fund(FNR),grant reference PRIDE17/12246511/PACEin part by the Austrian Science Fund(FWF)10.55776/COE5.We would like to acknowledge Christoph Schattauer and Mohamed Ali Abdulmalik for fruitful discussions.
文摘Calculating the impact of point defects on the macroscopic properties of technologically relevantsemiconductors remains a considerable challenge. Semi-empirical approaches, such as the tightbindingmethod, are very efficient in calculating the electronic structure of large supercells containingone or several defects. However, the accuracy of these calculations depends on the quality of theparameters. Obtaining reliable parameters by fitting to the large number of entangled bands indefective supercells is a demanding task.We therefore present an alternative way by fitting to the atomand orbital projected densities of states. Starting with a tight-binding fit of the pristine material,we onlyneed a few physically motivated parameters for the fitting of defects. The training is done on data setsgenerated purely with parameter variations of tight-binding Hamiltonians. We demonstrate theefficiency of our approach for the calculation of the carbon monomer and the carbon dimersubstitutions in hexagonal boron nitride. The method opens a path towards understandingcomplicated defect landscapes using a computationally affordable semi-empirical approach withoutsacrificing accuracy.
基金the National Natural Science Foundation of China and Shenhua Group Corp(No.U1261103)the National Natural Science Foundation of China(Nos.20771080)the Open Fund of State Key Laboratory of Coal Conversion,Institute of Coal Chemistry,Chinese Academy of Sciences,(No.J12-13-913).
文摘First-principles calculations are carried out to examine the adsorption of acetylene over the Pd(111)surface.A hydrogen adsorption system is initially investigated to confirm the reliability of the selected calculation method.Adsorption energies,Mulliken-populations,overlap populations,charge density,and projected density of states(PDOS)are then calculated in the optimised acetylene adsorption system.Results show that C_(2)H_(2) molecule tends to adsorb through the threefold parallel-bridge configuration that is computed to be the most stable.In this structure,the distance of the C-H bond is calculated to be 1.09 Å,and the C-C-H bond angle is 128°.The distance of the C-C bond in acetylene is 1.36 Å,increasing from 1.21 Å in the gas phase.Moreover,the C-C bond overlap population decreases from 1.98 to 1.38,revealing that the carbon configuration in C2H2 rehybridises from sp to sp^(2) and beyond.The obtained results are compared with available experimental studies on acetylene hydrogenation on single-metal surfaces.The PDOS study indicates that a carbonaceous layer may generate on the metal surface during acetylene adsorption.The carbonaceous layer can affect the adsorption and reaction of acetylene,thereby inactivating the metal surface.Our experiments also show that Pd exhibits high catalytic activity.
基金This work was supported by the National Natural Science Foundation of China(NSFC)(Grant No.20173031).
文摘The density functional theory(DFT)combining with the non-equilibrium Green functions(NEGF)method is applied to the study of the electronic transport properties for a Di-thiol-benzene(DTB)molecule coupled to two Au(111)surfaces.The dependence of the transport properties on the bias,the coupling geometry of the molecule-electrode interface,and the intermolecular interaction are examined in detail.The results show that the existence of the hydrogen atom at the end of the DTB molecule would significantly decrease the transmission coefficients,and then the differential conductance(dI/dV).By changing the position of the DTB molecule located between two electrodes a maximum value of calculated current is observed.It is also found that the intermolecular interaction will strongly influence the transport properties of the system studied.
