R-T instability model of magnetic fluid and its numerical simulations

The Rayleigh-Taylor(R-T) instability of ferrofluid has been the subject of recent research,because of its implications on the stability of stellar.By neglecting the viscosity and rotation of magnetic fluid,and assuming that the magnetic particles are irrotational and temperature insensitive,we obtain a simplified R-T instability model of magnetic fluid.For the interface tracing,we use five-order weighted essentially non-oscillatory(WENO) scheme to spatial direction and three-order TVD R-K method to time direction on the uniform mesh,respectively.If the direction of the external magnetic field is the same as that of gravity,the velocities of the interface will be increased.But if the direction of the external magnetic field is in opposition to the direction of gravity,the velocities of the interface will be decreased.When the direction of the external magnetic field is perpendicular to the direction of gravity,the symmetry of the interface will be destroyed.Because of the action which is produced by perpendicular external magnetic field,there are other bubbles at the boudaries which parallel the direction of gravity.When we increase the magnetic susceptibility of the magnetic fluids,the effects of external magnetic fields will be more distinct for the interface tracing.     

A density functional theory study of the geometric and electronic structure of MgF2 (110) surface

Ab initio density functional theory (DFT) was employed to study geometric and electronic structure of MgF2 (110) surface. Three different clean surface models have been considered. The results show that the surface terminated with one-layer F has the smallest relaxation and the lowest surface energy, which indicates this model is the most energetically favorable structure of MgF2(110) surface. Furthermore, the electronic properties are also discussed from the point of density of states and charge density. Analysis of electronic structure shows that the band gap of the surface is significantly narrowed with respect to the bulk. The electrons of the surface exhibit strong locality and larger effective mass.     

Microprobe of structure of crystal/liquid interface boundary layers

The molecular structures and its evolutive regularities within the boundary layers in the crystal growth of KDP and DKDP have been studied in real time by using holography and Raman mi-croprobe. The experiments show that the molecular structure of mother solution within the boundary layers is distinctly different from that of the solutions alone. In this paper, the effects of cations within the boundary layers on the structure of solution are considered. Within the characteristic boundary layers, the effects of cations cause the changes in O-P-O bond angle, electronic density redistribution of the phosphate groups, and significant changes in the bond intensity, thus leading to the breaking of partial hydrogen bonds of the phosphate associations, the readjustment of geometry of anionic phosphate groups and desolvation, and the forming of the smectic ordering structure of the anions-cations. Finally, the crystallization unit of anion-cation should be formed at the proximate interface.     

Optimization Methodology of Empirical Electronic Theory by Employing Statistical Model

An optimization methodology of empirical electronic theory(EET)for solids and molecules has been developed by employing a statistical model in this study.The current paper calculates the hybridization states of different atoms in some crystal structures and succeeds in predicting valence states of atoms.The prediction ofγ-Fe hybridization states based on statistics is found to be in reasonable agreement with early measurements.Through calculating Cr alloy austenite and Cr alloy martensite,the statistical results proved stable for each atom,and it is found that the valence electron structure of an atom depends on its element type and location in the crystal cell;finally,wear resistant steel with1 wt% C is designed by using a statistical model which is consistent with traditional empirical design.     

First Principle Calculation of Electromagnetic Mechanism for Fe_2Si Bulk Material

The electronic structure and the magnetic properties of Fe_2Si bulk have been calculated by the first-principle density function theory method. The band structure shows that the hexagonal Fe~2 Si bulk is ferromagnetic which is a metal structure under spin-up, and a semiconductor with the band gap of 0.518 eV under spin-down. The density of states shows the Fe~1 3d–spin and Fe~3 3d–spin in the electronic system are the main factors that is the source of the ferromagnetic properties of Fe_2Si bulk. The electronic structure Si-ions is 3s23p6 and that of Fe-ions is e_g~2↑e_g~(*1)↓t_(2g)~3↑. The molecular magnetic moment of Fe_2Si is 2.00 μB. The potential diagram of Fe_2Si bulk shows the formation of covalent and ionic bonds between the Fe atom and the Si atom, it leads to the center charge of Fe is polarized and off center position. These special properties of Fe_2Si bulk are mainly caused by d-d exchange and p-d hybridization. The results offer a certain reference for the magnetic semiconductor Fe_2Si material.     

Calculated structure, elastic and electronic properties of Mg2Pb at high pressure

The effects of high pressure on structure,elastic and electronic properties of the intermetallic Mg₂Pb were calculated by the first-principles plane wave pseudo-potential method in the scheme of density functional theory（DFT）within the generalized gradient approximation.The elastic constants and Debye temperature obtained at 0 GPa are in good agreement with the available experiment data and other theoretical results.The electronic properties calculated suggest that the electronic density of states（DOS）at the Fermi level decreases under high pressure.     

First-principles Investigation of the Structural,Electronic and Elastic Properties of Al2Ca and Al4Sr Phases in Mg-Al-Ca（Sr） Alloy

First-principles calculations have been carried out to investigate the structural stabilities, electronic structures and elastic properties of Mg17Al12, Al2Ca and Al4Sr phases. The optimized structural parameters are in good agreement with the experimental and other theoretical values. The calculated formation enthalpies and cohesive energies show that Al2Ca has the strongest alloying ability, and Al4Sr has the highest structural stability. The densities of states （DOS）, Mulliken electronic populations, and electronic charge density difference are obtained to reveal the underlying mechanism of structural stability. The bulk modulus, shear modulus, Young＇s modulus, and Poisson＇s ratio are estimated from the calculated elastic constants. The mechanical properties of these phases are further analyzed and discussed. The Gibbs free energy and Debye temperature are also calculated and discussed.     

Electronic structure and properties of pure cobalt

According to one-atom theory of pure metals,the electronic structure of hcp α-Co has been determined to be [Ar](3dn)0.46(3dm)1.86(3dc)5045(3se)0.03(4sf)1.30.The potential curve,cohesiw energy,lattice parameter,magnetism,elasticity and temperature dependences of specific heat and linear thermal expansion coefficient of the hcp α-Co are calculated.The theoretical values of these properties are compared with those obtained from experiments and calculated by LSDA and GGA methods.Three possible states ψβ(dn→dc),ψβ(dm→dc) and ψβ(sf→dc) for fcc β-Co are designed.The conversion of hcp α-Co→fcc β-Co occurs due to the increase of covalent electrons in state t2g Because the differences in the states,bond parameters and properties between hcp α-Co and fcc β-Co are very small,the two forms normally coexist at room temperature.     

Nucleation barrier of fcc(γ)→hcp(ε) martensitic transformation in Fe-based alloys

Based on the dislocation theory and Olson's stacking fault model, a model describing the nucleation of an hcp(ε) martensite embryo at low-angle grain boundary is proposed with the influence of external stress field taken into account. The dependences of temperature (T), shear stress (τ) and dislocation density at grain boundary on the martensite nucleation in FeMnSi based alloy, as an example, are numerically simulated. It has been shown that there exist the subcritical and critical embryos during the course of ε-phase nucleation. The free energy difference between them is just the energy barrier of embryo growth. Depending on T and τ, the characteristic embryo sizes may vary in wide ranges and decrease with increasing a and decreasing T. The energy condition of martensitic transformation at Ms and critical shear stress (τc) is discussed from the viewpoint of kinetics and thus the TEM observed result that stacking fault energy is not zero at Ms temperature is reasonably explained. Besides, it is pr     

Study of vehicle accident reconstruction based on the information of the tire marks

The tire mark is the important legacy information left at the accident scene. Based on the vehicle collision dynamics model, this study provided an optimized algorithm with vehicle final location and other related information for the tire marks. When the tire marks simulation results fit the real one well, the state of vehicle can be understood as the real state in the accident. Based on above, the vehicle velocity and direction are decided. According to the velocity and direction of the vehicle, the complete accident process can be simulated. With the help of the Pc-Crash software, the method has been applied in typical collision accident cases analysis. The reconstruction results will provide the scientific and numerical references for vehicle collision accidents analyzing and appraising.     

Fe@Au8团簇的几何结构和电子特性

利用密度泛函PW91方法研究了Fe@Au8团簇的平衡结构和电子性能,获得了多个异构体及电子态.结果显示Fe原子在低能异构体中趋于占据最高配位位置,相似异构体的能量随着Fe原子配位数减少而增加.电子性能分析表明基态结构具有较高的稳定性,类似最稳定Au9团簇的I2异构体有相对大的HOMO-LUMO能级间隙.     

Fe@Au8团簇的几何结构和电子特性

利用密度泛函PW91方法研究了Fe@Au8团簇的平衡结构和电子性能,获得了多个异构体及电子态。结果显示Fe原子在低能异构体中趋于占据最高配位位置,相似异构体的能量随着Fe原子配位数减少而增加。电子性能分析表明基态结构具有较高的稳定性,类似最稳定Au9团簇的12异构体有相对大的HOMO—LUMO能级间隙。     

Mn掺杂c-ZrO2电子和光学性质的第一性原理研究

基于DFT+U第一性原理计算,预测了过渡金属锰（Mn）掺杂立方氧化锆（c-ZrO₂）体系的电子和光学性质。当c-ZrO₂中的Zr原子被Mn原子取代后,体系的电子态密度图表明体系的带隙减小,同时价带顶的电子密度明显增加使得价带展宽约5%。在自旋向上通道中,费米面附近的电子密度源于Mn 3d电子与O 2p电子的强烈混合,使得掺杂体系具有半金属铁磁性能,这也可能是引起体系带隙减小的原因。本研究还表明,通过Mn掺杂,体系折射率明显增加,在约为2.8 eV 低能区域形成新的坡度陡峭的光吸收峰,这一发现使Mn掺杂c-ZrO₂用作光吸收材料成为可能。通过Zener双交换机制解释了体系的铁磁性能,该理论也曾用于解释其他化合物;同时也探讨了体系的电子结构和光学性质之间的联系。     

钙钛矿电子结构的密度泛函理论研究

应用密度泛函理论(DFT)计算方法,优化了K2Ti2O5的稳定几何构型,并计算了此钙钛矿体系的能带结构和态密度等基态物理性质.结果表明,K2Ti2O5属于间接绝缘体氧化物,其理论带隙宽度为2.6 eV.Ti原子处于氧原子的中心,其d轨道分裂为能量较高的eg和能量较低的t2g轨道,各轨道都靠近费米能级变为占据或半占据状态...     

磁性石墨烯结构中自旋波的性质

为了了解自旋波在磁性石墨烯结构中的传播性质,采用格林函数方法和海森堡模型研究了磁性石墨烯结构中的自旋波频率和自旋波态密度,分析了温度、外磁场和各向异性对自旋波谱和自旋波态密度的影响.结果表明,在整个布里渊区Γ-M-K-Γ中,自旋波频率和自旋波态密度随约化温度的升高而减小.随着外磁场强度的增加,自旋波频率和自旋波态密度均随之增加.随着各向异性的增加,自旋波频率和自旋波态密度均呈现微小程度的提高.在布里渊区M-K中,温度、外磁场和各向异性对自旋波谱的影响较大.     

Electronic Structure and Chemical Bond of Ti3SiC2 and Adding Al Element

The relation among electronic structure, chemical bond and property of Ti3SiC2 and Al-doped was studied by density function and discrete variation （ DFT- DVM） method. When Al element is added into Ti3 SiC2 , there is a less difference of ionic bond, which does not play a leading role to influent the properties. After adding Al, the covalent bond of Al and the near Ti becomes somewhat weaker, but the covalent bond of Al and the Si in the same layer is obviously stronger than that of Si and Si before adding. Therefore, in preparation of Ti3 SiC2 , adding a proper quantity of Al can promote the formation of Ti3 SiC2 . The density of stnte shows that there is a mixed conductor character in both of Ti3 SiC2 and adding Al element. Ti3 SiC2 is with more tendencies to form a semiconductor. The total density of state near Fermi lever after adding Al is larger than that before adding, so the electric conductivity may increase after adding Al.     

晶体场中第一过渡型离子轨道分裂及宝石呈色机理

应用量子力学、群论及晶体场理论，研究第一过渡型金属离子的3d轨道在不同对称性的晶体场中的分裂，以及3d电子在分裂轨道上的分布。并且通过研究d轨道能级分裂图和入射光使电子跃迁所产生的吸收光谱特征，结合实验测量结果，来解释宝石矿物的特征颜色和多色性成因。由此提供了研究宝石成色机理和宝石优化处理的理论依据。     

碳纳米管超晶格结构的第一性原理

针对掺杂N、B、Si的碳纳米管超晶格的电子结构及拉伸性能,运用第一性原理进行了相关研究.结果表明,碳纳米管超晶格会形成类似管状结构.不同掺杂元素导致碳纳米管超晶格的结构稳定性有所不同.碳纳米管经掺杂后,能带中的能隙由半导体性转变为金属性,且费米能级处的态密度值增大,表明碳纳米管超晶格的物理化学活性增强,而结构稳定性降低.对于碳纳米管超晶格而言,结构稳定性从高至低依次为3×1碳氮、1×1碳硼和3×1碳硼纳米管超晶格.     

硅（100）表面组装膜的第一性原理研究

应用基于密度泛函理论的第一原理计算研究硅（100）表面芳香烃重氮盐自组装单层膜的键长、键角和能量的改变.通过模拟计算,可以确定自组装膜的稳定结构和结合能.计算结果显示,单晶硅表面在自组装前后部分键长和键角发生了明显的改变.整个自组装系统减少的能量是-101.95eV,该能量是形成Si-C共价键释放出的结合能,说明芳香烃重氮盐和单晶硅（100）表面很容易形成自组装单层膜.自组装后的系统稳定性很好,证明硅表面的单层膜结合的很牢固.