There are five most widely used contact angle schemes in the pseudopotential lattice Boltzmann(LB)model for simulating the wetting phenomenon:The pseudopotential-based scheme(PB scheme),the improved virtualdensity sch...There are five most widely used contact angle schemes in the pseudopotential lattice Boltzmann(LB)model for simulating the wetting phenomenon:The pseudopotential-based scheme(PB scheme),the improved virtualdensity scheme(IVD scheme),the modified pseudopotential-based scheme with a ghost fluid layer constructed by using the fluid layer density above the wall(MPB-C scheme),the modified pseudopotential-based scheme with a ghost fluid layer constructed by using the weighted average density of surrounding fluid nodes(MPB-W scheme)and the geometric formulation scheme(GF scheme).But the numerical stability and accuracy of the schemes for wetting simulation remain unclear in the past.In this paper,the numerical stability and accuracy of these schemes are clarified for the first time,by applying the five widely used contact angle schemes to simulate a two-dimensional(2D)sessile droplet on wall and capillary imbibition in a 2D channel as the examples of static wetting and dynamic wetting simulations respectively.(i)It is shown that the simulated contact angles by the GF scheme are consistent at different density ratios for the same prescribed contact angle,but the simulated contact angles by the PB scheme,IVD scheme,MPB-C scheme and MPB-W scheme change with density ratios for the same fluid-solid interaction strength.The PB scheme is found to be the most unstable scheme for simulating static wetting at increased density ratios.(ii)Although the spurious velocity increases with the increased liquid/vapor density ratio for all the contact angle schemes,the magnitude of the spurious velocity in the PB scheme,IVD scheme and GF scheme are smaller than that in the MPB-C scheme and MPB-W scheme.(iii)The fluid density variation near the wall in the PB scheme is the most significant,and the variation can be diminished in the IVD scheme,MPB-C scheme andMPBWscheme.The variation totally disappeared in the GF scheme.(iv)For the simulation of capillary imbibition,the MPB-C scheme,MPB-Wscheme and GF scheme simulate the dynamics of the liquid-vapor interface well,with the GF scheme being the most accurate.The accuracy of the IVD scheme is low at a small contact angle(44 degrees)but gets high at a large contact angle(60 degrees).However,the PB scheme is the most inaccurate in simulating the dynamics of the liquid-vapor interface.As a whole,it is most suggested to apply the GF scheme to simulate static wetting or dynamic wetting,while it is the least suggested to use the PB scheme to simulate static wetting or dynamic wetting.展开更多
The dynamics of the cavitation bubble collapse is a fundamental issue for the bubble collapse application and prevention. In the present work, the modified forcing scheme for the pseudopotential multi-relaxation-time ...The dynamics of the cavitation bubble collapse is a fundamental issue for the bubble collapse application and prevention. In the present work, the modified forcing scheme for the pseudopotential multi-relaxation-time lattice Boltzmann model developed by Li Q et al. [ Li Q, Luo K H and Li X J 2013 Phys. Rev. E 87 053301] is adopted to develop a cavitation bubble collapse model. In the respects of coexistence curves and Laplace law verification, the improved pseudopotential multi-relaxation-time lattice Boltzmann model is investigated. It is found that the thermodynamic consistency and surface tension are independent of kinematic viscosity. By homogeneous and heterogeneous cavitation simulation, the ability of the present model to describe the cavitation bubble development as well as the cavitation inception is verified. The bubble collapse between two parallel walls is simulated. The dynamic process of a collapsing bubble is consistent with the results from experiments and simulations by other numerical methods. It is demonstrated that the present pseudopotential multirelaxation-time lattice Boltzmann model is applicable and efficient, and the lattice Boltzmann method is an alternative tool for collapsing bubble modeling.展开更多
Cavitation bubble collapse near rough solid wall is modeled by the multi-relaxation-time (MRT) pseudopotential lattice Boltzmann (LB) model. The modified forcing scheme, which can achieve LB model’s thermodynamic con...Cavitation bubble collapse near rough solid wall is modeled by the multi-relaxation-time (MRT) pseudopotential lattice Boltzmann (LB) model. The modified forcing scheme, which can achieve LB model’s thermodynamic consistency by tuning a parameter related with the particle interaction range, is adopted to achieve desired stability and density ratio. The bubble collapse near rough solid wall was simulated by the improved MRT pseudopotential LB model. The mechanism of bubble collapse is studied by investigating the bubble profiles, pressure field and velocity field evolution. The eroding effects of collapsing bubble are analyzed in details. It is found that the process and the effect of the interaction between bubble collapse and rough solid wall are affected seriously by the geometry of solid boundary. At the same time, it demonstrates that the MRT pseudopotential LB model is a potential tool for the investigation of the interaction mechanism between the collapsing bubble and complex geometry boundary.展开更多
The method of splitting a plane-wave finite-difference time-domain (SP-FDTD) algorithm is presented for the initiation of plane-wave source in the total-field / scattered-field (TF/SF) formulation of high-order sy...The method of splitting a plane-wave finite-difference time-domain (SP-FDTD) algorithm is presented for the initiation of plane-wave source in the total-field / scattered-field (TF/SF) formulation of high-order symplectic finite- difference time-domain (SFDTD) scheme for the first time. By splitting the fields on one-dimensional grid and using the nature of numerical plane-wave in finite-difference time-domain (FDTD), the identical dispersion relation can be obtained and proved between the one-dimensional and three-dimensional grids. An efficient plane-wave source is simulated on one-dimensional grid and a perfect match can be achieved for a plane-wave propagating at any angle forming an integer grid cell ratio. Numerical simulations show that the method is valid for SFDTD and the residual field in SF region is shrinked down to -300 dB.展开更多
Different classes of first-principle pseudopotentials are compared and various schemes for pseudo-potential generation based on norm conservation are discussed in this paper.BHS(Bachelet,Hamann,and Schlueter)-scheme a...Different classes of first-principle pseudopotentials are compared and various schemes for pseudo-potential generation based on norm conservation are discussed in this paper.BHS(Bachelet,Hamann,and Schlueter)-scheme and V(Vanderbilt)-modifications are used to derive the KB(Kleinman and Bylander).pseudopotentials and pseudo wave functions of bismuth.Quality test of pseudopotemtials shows tha no ghost states occur in the logarithmic deriuatives of pseudo wave functions of Bismuth,The obtained bond length of bismuth dimer with this type of pseudopotentials is in good agreement with previous accurately calculated ab initio quantum chemical result.展开更多
The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect.The complexity of this topic is that the cavitation bu...The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect.The complexity of this topic is that the cavitation bubble collapse includes many extreme physical phenomena and variability of different solid surface properties.In the present work,the cavitation bubble collapse in hydrophobic concave is studied using the pseudopotential multi-relaxation-time lattice Boltzmann model(MRT-LB).The model is modified by involving the piecewise linear equation of state and improved forcing scheme.The fluid-solid interaction in the model is employed to adjust the wettability of solid surface.Moreover,the validity of the model is verified by comparison with experimental results and grid-independence verification.Finally,the cavitation bubble collapse in a hydrophobic concave is studied by investigating density field,pressure field,collapse time,and jet velocity.The superimposed effect of the surface hydrophobicity and concave geometry is analyzed and explained in the framework of the pseudopotential LBM.The study shows that the hydrophobic concave can enhance cavitation effect by decreasing cavitation threshold,accelerating collapse and increasing jet velocity.展开更多
在有我们的很好确定的单身的参量的模型潜力的第二份订单以外的 pseudopotential 理论被采用计算全部的水晶精力,静态的体积模量,在Jones地区脸和 Si 的压力卷关系(在压力下面的状态的方程)上的点 X 的精力乐队差距,用 Nagy 的静态...在有我们的很好确定的单身的参量的模型潜力的第二份订单以外的 pseudopotential 理论被采用计算全部的水晶精力,静态的体积模量,在Jones地区脸和 Si 的压力卷关系(在压力下面的状态的方程)上的点 X 的精力乐队差距,用 Nagy 的静态的本地域修正的 Ge 和 -Sn 工作。结果与那些相比使用很少获得另外的本地地修正功能。全部的精力的现在的结果在对试验性的数据的好同意。屏蔽功能完美地与 Ge 和 -Sn 的试验性的结果正在匹配的由 Nagy 的家计算的体积模量。一些偏差在精力乐队差距的价值被发现。展开更多
Based on the method developed by Nucci,the pseudopotentials,Lax pairs and the singularity manifoldequations of the generalized fifth-order KdV equation are derived.By choosing different coefficient,the correspondingre...Based on the method developed by Nucci,the pseudopotentials,Lax pairs and the singularity manifoldequations of the generalized fifth-order KdV equation are derived.By choosing different coefficient,the correspondingresults and the Backlund transformations can be obtained on three conditioners which include Caudrey-Dodd-GibbonSawada-Kotera equation,the Lax equation and the Kaup-kupershmidt equation.展开更多
We introduce a first-principles density-fumctional theory,i.e.the finite-differcnce pseudopotential density-functional theory in real space and the langevin molecular dynamics annealing technique,to the descriptions o...We introduce a first-principles density-fumctional theory,i.e.the finite-differcnce pseudopotential density-functional theory in real space and the langevin molecular dynamics annealing technique,to the descriptions of structures and some properties of small carbon clusters(CN,N=2-8).It is shown that the odd-numbered clusters have linear structures and most of the even-numbered clusters prefer cyclic structures.展开更多
The Gibbs-Bogoliubov (GB) inequality is applied to investigate the thermodynamic properties of someequiatomic noble metal alloys in liquid phase such as Au-Cu,Ag-Cu,and Ag-Au using well recognized pseudopotentialforma...The Gibbs-Bogoliubov (GB) inequality is applied to investigate the thermodynamic properties of someequiatomic noble metal alloys in liquid phase such as Au-Cu,Ag-Cu,and Ag-Au using well recognized pseudopotentialformalism.For description of the structure,well known Percus-Yevick (PY) hard sphere model is used as a referencesystem.By applying a variation method the best hard core diameters have been found which correspond to minimumfree energy.With this procedure the thermodynamic properties such as entropy and heat of mixing have been computed.The influence of local held correction function viz;Hartree (H),Taylor (T),Ichimaru-Utsumi (IU),Farid et al.(F),and Sarkar et al.(S) is also investigated.The computed results of the excess entropy compares favourably in the caseof liquid alloys while the agreement with experiment is poor in the case of heats of mixing.This may be due to thesensitivity of the heats of mixing with the potential parameters and the dielectric function.展开更多
We have studied the structural and atomic transport properties of liquid f-shell Yb in the temperature range 1123 K–1473 K. Pair interactions between atoms are derived using a local pseudopotential. The potential par...We have studied the structural and atomic transport properties of liquid f-shell Yb in the temperature range 1123 K–1473 K. Pair interactions between atoms are derived using a local pseudopotential. The potential parameters are fitted to the phonon dispersion curve at room temperature. The local pseudopotential used in the present study is computationally more efficient with only three parameters, and it is found to be transferable to the liquid phase without changing the parameters.Since the various computed properties agree with reported theoretical and experimental findings, the adopted fitting scheme is justified. As a significant outcome of the study, we find that(i) the melting in Yb is governed by the Lindemann's law,(ii)the mass transport mechanism obeys the Arrhenius law,(iii) the role of the three-particle correlation function in deriving the velocity autocorrelation function is small,(iv) the mean-square atomic displacement is more sensitive to the choice of interaction potential than the other bulk properties, and(v) liquid Yb does not show liquid–liquid phase transition within the studied temperature range. Further, due to the good description of the structural and mass transport properties, we propose that Yb remains divalent at reduced density.展开更多
Within the framework of the density functional theory and the pseudopotential method,the electronic structure calculations of the“metal-Si(100)”systems with Li,Be and Al as metal coverings of one to four monolayers(...Within the framework of the density functional theory and the pseudopotential method,the electronic structure calculations of the“metal-Si(100)”systems with Li,Be and Al as metal coverings of one to four monolayers(ML)thickness,were carried out.Calculations showed that band gaps of 1.02 eV,0.98 eV and 0.5 eV,respectively,appear in the densities of electronic states when the thickness of Li,Be and Al coverings is one ML.These gaps disappear with increasing thickness of the metal layers:first in the Li-Si system(for two ML),then in the Al-Si system(for three ML)and then in the Be-Si system(for four ML).This behavior of the band gap can be explained by the passivation of the substrate surface states and the peculiarities of the electronic structure of the adsorbed metals.In common the results can be interpreted as describing the possibility of the formation of a two-dimensional silicide with semiconducting properties in Li-Si(100),Be-Si(100)and Al-Si(100)systems.展开更多
A first principles study of the electronic properties and bulk modulus (B0) of the fcc and bcc transition metals, transition metal carbides and nitrides is presented. The calculations were performed by plane-wave ps...A first principles study of the electronic properties and bulk modulus (B0) of the fcc and bcc transition metals, transition metal carbides and nitrides is presented. The calculations were performed by plane-wave pseudopotential method in the framework of the density functional theory with local density approximation. The density of states and the valence charge densities of these solids are plotted. The results show that B0 does not vary monotonically when the number of the valence d electrons increases. B0 reaches a maximum and then decreases for each of the four sorts of solids. It is related to the occupation of the bonding and anti-bonding states in the solid. The value of the valence charge density at the midpoint between the two nearest metal atoms tends to be proportional to B0.展开更多
基金sponsored by the National Natural Science Foundation of China under Grant No.52206101Shanghai Sailing Program under Grant No.20YF1431200the Experiments for Space Exploration Program and the Qian Xuesen Laboratory,China Academy of Space Technology under Grant No.TKTSPY-2020-01-01.
文摘There are five most widely used contact angle schemes in the pseudopotential lattice Boltzmann(LB)model for simulating the wetting phenomenon:The pseudopotential-based scheme(PB scheme),the improved virtualdensity scheme(IVD scheme),the modified pseudopotential-based scheme with a ghost fluid layer constructed by using the fluid layer density above the wall(MPB-C scheme),the modified pseudopotential-based scheme with a ghost fluid layer constructed by using the weighted average density of surrounding fluid nodes(MPB-W scheme)and the geometric formulation scheme(GF scheme).But the numerical stability and accuracy of the schemes for wetting simulation remain unclear in the past.In this paper,the numerical stability and accuracy of these schemes are clarified for the first time,by applying the five widely used contact angle schemes to simulate a two-dimensional(2D)sessile droplet on wall and capillary imbibition in a 2D channel as the examples of static wetting and dynamic wetting simulations respectively.(i)It is shown that the simulated contact angles by the GF scheme are consistent at different density ratios for the same prescribed contact angle,but the simulated contact angles by the PB scheme,IVD scheme,MPB-C scheme and MPB-W scheme change with density ratios for the same fluid-solid interaction strength.The PB scheme is found to be the most unstable scheme for simulating static wetting at increased density ratios.(ii)Although the spurious velocity increases with the increased liquid/vapor density ratio for all the contact angle schemes,the magnitude of the spurious velocity in the PB scheme,IVD scheme and GF scheme are smaller than that in the MPB-C scheme and MPB-W scheme.(iii)The fluid density variation near the wall in the PB scheme is the most significant,and the variation can be diminished in the IVD scheme,MPB-C scheme andMPBWscheme.The variation totally disappeared in the GF scheme.(iv)For the simulation of capillary imbibition,the MPB-C scheme,MPB-Wscheme and GF scheme simulate the dynamics of the liquid-vapor interface well,with the GF scheme being the most accurate.The accuracy of the IVD scheme is low at a small contact angle(44 degrees)but gets high at a large contact angle(60 degrees).However,the PB scheme is the most inaccurate in simulating the dynamics of the liquid-vapor interface.As a whole,it is most suggested to apply the GF scheme to simulate static wetting or dynamic wetting,while it is the least suggested to use the PB scheme to simulate static wetting or dynamic wetting.
基金supported by the National Natural Science Foundation of China(Grant Nos.11274092 and 1140040119)the Natural Science Foundation of Jiangsu Province,China(Grant No.SBK2014043338)
文摘The dynamics of the cavitation bubble collapse is a fundamental issue for the bubble collapse application and prevention. In the present work, the modified forcing scheme for the pseudopotential multi-relaxation-time lattice Boltzmann model developed by Li Q et al. [ Li Q, Luo K H and Li X J 2013 Phys. Rev. E 87 053301] is adopted to develop a cavitation bubble collapse model. In the respects of coexistence curves and Laplace law verification, the improved pseudopotential multi-relaxation-time lattice Boltzmann model is investigated. It is found that the thermodynamic consistency and surface tension are independent of kinematic viscosity. By homogeneous and heterogeneous cavitation simulation, the ability of the present model to describe the cavitation bubble development as well as the cavitation inception is verified. The bubble collapse between two parallel walls is simulated. The dynamic process of a collapsing bubble is consistent with the results from experiments and simulations by other numerical methods. It is demonstrated that the present pseudopotential multirelaxation-time lattice Boltzmann model is applicable and efficient, and the lattice Boltzmann method is an alternative tool for collapsing bubble modeling.
文摘Cavitation bubble collapse near rough solid wall is modeled by the multi-relaxation-time (MRT) pseudopotential lattice Boltzmann (LB) model. The modified forcing scheme, which can achieve LB model’s thermodynamic consistency by tuning a parameter related with the particle interaction range, is adopted to achieve desired stability and density ratio. The bubble collapse near rough solid wall was simulated by the improved MRT pseudopotential LB model. The mechanism of bubble collapse is studied by investigating the bubble profiles, pressure field and velocity field evolution. The eroding effects of collapsing bubble are analyzed in details. It is found that the process and the effect of the interaction between bubble collapse and rough solid wall are affected seriously by the geometry of solid boundary. At the same time, it demonstrates that the MRT pseudopotential LB model is a potential tool for the investigation of the interaction mechanism between the collapsing bubble and complex geometry boundary.
基金supported by the National Natural Science Foundation of China(Grant Nos.60931002 and 61101064)the Universities Natural Science Foundation of Anhui Province,China(Grant Nos.KJ2011A002 and 1108085J01)
文摘The method of splitting a plane-wave finite-difference time-domain (SP-FDTD) algorithm is presented for the initiation of plane-wave source in the total-field / scattered-field (TF/SF) formulation of high-order symplectic finite- difference time-domain (SFDTD) scheme for the first time. By splitting the fields on one-dimensional grid and using the nature of numerical plane-wave in finite-difference time-domain (FDTD), the identical dispersion relation can be obtained and proved between the one-dimensional and three-dimensional grids. An efficient plane-wave source is simulated on one-dimensional grid and a perfect match can be achieved for a plane-wave propagating at any angle forming an integer grid cell ratio. Numerical simulations show that the method is valid for SFDTD and the residual field in SF region is shrinked down to -300 dB.
文摘Different classes of first-principle pseudopotentials are compared and various schemes for pseudo-potential generation based on norm conservation are discussed in this paper.BHS(Bachelet,Hamann,and Schlueter)-scheme and V(Vanderbilt)-modifications are used to derive the KB(Kleinman and Bylander).pseudopotentials and pseudo wave functions of bismuth.Quality test of pseudopotemtials shows tha no ghost states occur in the logarithmic deriuatives of pseudo wave functions of Bismuth,The obtained bond length of bismuth dimer with this type of pseudopotentials is in good agreement with previous accurately calculated ab initio quantum chemical result.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11874140 and 11574072)the Fund from the State Key Laboratory of Acoustics,Chinese Academy of Sciences(Grant No.SKLA201913)+1 种基金the National Key Research and Development Program of China(Grant No.2016YFC0401600)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(Grant Nos.2018B741X14 and KYCX180552)。
文摘The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect.The complexity of this topic is that the cavitation bubble collapse includes many extreme physical phenomena and variability of different solid surface properties.In the present work,the cavitation bubble collapse in hydrophobic concave is studied using the pseudopotential multi-relaxation-time lattice Boltzmann model(MRT-LB).The model is modified by involving the piecewise linear equation of state and improved forcing scheme.The fluid-solid interaction in the model is employed to adjust the wettability of solid surface.Moreover,the validity of the model is verified by comparison with experimental results and grid-independence verification.Finally,the cavitation bubble collapse in a hydrophobic concave is studied by investigating density field,pressure field,collapse time,and jet velocity.The superimposed effect of the surface hydrophobicity and concave geometry is analyzed and explained in the framework of the pseudopotential LBM.The study shows that the hydrophobic concave can enhance cavitation effect by decreasing cavitation threshold,accelerating collapse and increasing jet velocity.
文摘在有我们的很好确定的单身的参量的模型潜力的第二份订单以外的 pseudopotential 理论被采用计算全部的水晶精力,静态的体积模量,在Jones地区脸和 Si 的压力卷关系(在压力下面的状态的方程)上的点 X 的精力乐队差距,用 Nagy 的静态的本地域修正的 Ge 和 -Sn 工作。结果与那些相比使用很少获得另外的本地地修正功能。全部的精力的现在的结果在对试验性的数据的好同意。屏蔽功能完美地与 Ge 和 -Sn 的试验性的结果正在匹配的由 Nagy 的家计算的体积模量。一些偏差在精力乐队差距的价值被发现。
基金Supported by the National Natural Science Foundation of China under Grant Nos.10735030,11075055,and 90718041the Shanghai Leading Academic Discipline Project,China under Grant No.B412+1 种基金the Program for Changjiang Scholars,the Innovative Research Team in University of Ministry of Education of China under Grant No.IRT 0734the K.C.Wong Magna Fund in Ningbo University
文摘Based on the method developed by Nucci,the pseudopotentials,Lax pairs and the singularity manifoldequations of the generalized fifth-order KdV equation are derived.By choosing different coefficient,the correspondingresults and the Backlund transformations can be obtained on three conditioners which include Caudrey-Dodd-GibbonSawada-Kotera equation,the Lax equation and the Kaup-kupershmidt equation.
基金The project supported by National Natural Science Foundation of China under Grant No.10274055
the Research Fund for the Doctoral Program of High Education of China under Grant No.20020610001
文摘We introduce a first-principles density-fumctional theory,i.e.the finite-differcnce pseudopotential density-functional theory in real space and the langevin molecular dynamics annealing technique,to the descriptions of structures and some properties of small carbon clusters(CN,N=2-8).It is shown that the odd-numbered clusters have linear structures and most of the even-numbered clusters prefer cyclic structures.
文摘The Gibbs-Bogoliubov (GB) inequality is applied to investigate the thermodynamic properties of someequiatomic noble metal alloys in liquid phase such as Au-Cu,Ag-Cu,and Ag-Au using well recognized pseudopotentialformalism.For description of the structure,well known Percus-Yevick (PY) hard sphere model is used as a referencesystem.By applying a variation method the best hard core diameters have been found which correspond to minimumfree energy.With this procedure the thermodynamic properties such as entropy and heat of mixing have been computed.The influence of local held correction function viz;Hartree (H),Taylor (T),Ichimaru-Utsumi (IU),Farid et al.(F),and Sarkar et al.(S) is also investigated.The computed results of the excess entropy compares favourably in the caseof liquid alloys while the agreement with experiment is poor in the case of heats of mixing.This may be due to thesensitivity of the heats of mixing with the potential parameters and the dielectric function.
文摘We have studied the structural and atomic transport properties of liquid f-shell Yb in the temperature range 1123 K–1473 K. Pair interactions between atoms are derived using a local pseudopotential. The potential parameters are fitted to the phonon dispersion curve at room temperature. The local pseudopotential used in the present study is computationally more efficient with only three parameters, and it is found to be transferable to the liquid phase without changing the parameters.Since the various computed properties agree with reported theoretical and experimental findings, the adopted fitting scheme is justified. As a significant outcome of the study, we find that(i) the melting in Yb is governed by the Lindemann's law,(ii)the mass transport mechanism obeys the Arrhenius law,(iii) the role of the three-particle correlation function in deriving the velocity autocorrelation function is small,(iv) the mean-square atomic displacement is more sensitive to the choice of interaction potential than the other bulk properties, and(v) liquid Yb does not show liquid–liquid phase transition within the studied temperature range. Further, due to the good description of the structural and mass transport properties, we propose that Yb remains divalent at reduced density.
文摘Within the framework of the density functional theory and the pseudopotential method,the electronic structure calculations of the“metal-Si(100)”systems with Li,Be and Al as metal coverings of one to four monolayers(ML)thickness,were carried out.Calculations showed that band gaps of 1.02 eV,0.98 eV and 0.5 eV,respectively,appear in the densities of electronic states when the thickness of Li,Be and Al coverings is one ML.These gaps disappear with increasing thickness of the metal layers:first in the Li-Si system(for two ML),then in the Al-Si system(for three ML)and then in the Be-Si system(for four ML).This behavior of the band gap can be explained by the passivation of the substrate surface states and the peculiarities of the electronic structure of the adsorbed metals.In common the results can be interpreted as describing the possibility of the formation of a two-dimensional silicide with semiconducting properties in Li-Si(100),Be-Si(100)and Al-Si(100)systems.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 50175082 and 10275049), and the Fund for the Doctoral Program of Higher Education (Grant No 2002486016).
文摘A first principles study of the electronic properties and bulk modulus (B0) of the fcc and bcc transition metals, transition metal carbides and nitrides is presented. The calculations were performed by plane-wave pseudopotential method in the framework of the density functional theory with local density approximation. The density of states and the valence charge densities of these solids are plotted. The results show that B0 does not vary monotonically when the number of the valence d electrons increases. B0 reaches a maximum and then decreases for each of the four sorts of solids. It is related to the occupation of the bonding and anti-bonding states in the solid. The value of the valence charge density at the midpoint between the two nearest metal atoms tends to be proportional to B0.