Hamaker微观连续介质理论的数字密度和Hamaker常数分析

针对Hamaker微观连续介质理论在微观接触力计算中存在的问题,根据Hamaker假设,用连续介质法计算2个原子之间的相互作用力,发现作用力同经典的Lennard-Jones势所反映的作用力不一致.通过分析数字密度,发现数字密度并非是如Hamaker所认为的常数,而是随间距变化的;并得到Hamaker微观连续介质理论仅在间距大于7倍的原子半径时才成立的结论.通过分析Hamaker常数,发现Hamaker常数也随间距变化.     

Dislocation energy and calculation from Peierls stress： a rigorous the lattice theory

In the classical Peierls--Nabarro (P-N) theory of dislocation, there is a long-standing contradiction that the stable configuration of dislocation has maximum energy rather than minimum energy. In this paper, the dislocation energy is calculated rigorously in the context of the full lattice theory. It is found that besides the misfit energy considered in the classical P-N theory, there is an extra elastic strain energy that is also associated with the discreteness of lattice. The contradiction can be automatically removed provided that the elastic strain energy associated with the discreteness is taken into account. This elastic strain energy is very important because its magnitude is larger than the misfit energy, its sign is opposite to the misfit energy. Since the elastic strain energy and misfit energy associated with discreteness cancel each other, and the width of dislocation becomes wide in the lattice theory, the Peierls energy, which measures the height of the effective potential barrier, becomes much smaller than that given in the classical P-N theory. The results calculated here agree with experimental data. Furthermore, based on the results obtained, a useful formula of the Peierls stress is proposed to fully include the discreteness effects.     

规则星形高分子之间的相互作用势的自洽场研究

用自洽场理论方法计算了星形高分子之间的相互作用势, 并与标度理论的推测以及基于粒子的分子动力学模拟方法的结果进行了比较. 自洽场理论计算得到的星形高分子之间的二体相互作用势与标度理论推测的结果基本一致: 当两个星形高分子核心之间的距离小于其对应的等效软球的半径R时, 二体相互作用势U与星形高分子核心之间的距离d及官能度f之间的关系为U(d)∝-f 3/2 ln(d/R). 当星形高分子核心间距离较小, 相互作用势与星形高分子核心间距离的对数呈线性关系时, 三体相互作用为吸引作用, 但其强度约等于二体作用的10%. 因此, 以二体作用为基础的基于粒子的模拟方法是基本合理的.     

一种可能的简并谱NNS分布

To expose the statistical properties of the degenerated spectrum, with the aid of the random matrix theory,a possible form of the NNS distribution function of the degenerate spectrum was proposed by providing a solution in terms of the same-degeneracy case. The results indicate that the target spectrum is transformed into two sub-spectra: a random one and a regular one, and that the repulsion level of the regular spectrum is also decreased.     

Si(001)-(2×2×1):H表面O2吸附的密度泛函理论研究

A novel model was developed to theoretically evaluate the O2 adsorption on H-terminated Si(001)-(2*2*1) surface. The periodic boundary condition, the ultrasoft pseudopotentials technique based on density functional theory (DFT) with generalized gradient approximation (GGA) functional were applied in our ab initio calculations. By analyzing bonding energy on site, the favourable adsorption site was determined. The calculations also predicted that the adsorption products should be Si=O and H2O. This theoretical study supported the reaction mechanism provided by Kovalev et al. The results were also a base for further investigation of some more complex systems such as the oxidation on porous silicon surface.     

洁净和氧吸附的Cu(100)表面重构的理论研究

The interaction of atomic oxygen with the clean Cu(100) surface has been studied by means of cluster and periodic slab models density functional theory in the present paper. The Cu(4,9,4) cluster and a three-layer slab with c(2×2) structure are used to model the perfect Cu(100) surface. Three possible adsorption sites,top, bridge and hollow site, were considered in the calculations. The predicted results show that the hollow site is the prefer site for atomic oxygen adsorbed on Cu(100) surface energetically. This is in good agreement with the experiment. The calculated binding energies are respective 2.014, 3.154 and 3.942 eV for top, bridge and hollow sites at mPW1PW91/LanL2dz level for the cluster model. The geometry of Cu(100) surface has also been optimized theoretically with various density functional methods and the results show that the prediction from the B3PW91/LanL2dz and mPW1PW91/LanL2dz reproduce the experimental observation.The frontier molecular orbitals and partial density of states analysis show that the electron transfer from the d orbital of substrate to the p orbital of the surface oxygen atom.     

吲唑、3-卤代吲唑互变异构反应机理的理论研究

The molecular structures of indazole and 3-halogeno-indazole tautomers were calculated by the B3LYP method at the 6-311G** level, both in the gaseous and aqueous phases, with full geometry optimization.The geometry and electronic structure of the tautomers of indazole, 3-halogeno-indazole and their transition states were obtained. The Onsager solvate theory model was employed for the aqueous solution calculations.The results of the calculation indicated that the N1-H form of the studied molecule is more stable than that of the N2-H form. The influences of the different 3-halogeno and solvent effects on the geometry, energy,charge and activation energy were discussed. The reaction mechanism of the tautomerization of indazole and 3-halogeno-indazole was also studied and a three-membered cyclic transition state of the tautomer reaction has been obtained.     

温度对α-Al2O3(0001)表面吸附生长ZnO影响的DFT研究

The adsorption and the growth of ZnO on α-Al2O3(0001) surface at various temperatures were theoretically calculated by using a plane wave pseudopotentials (USP) method based on density functional theory.The average adsorption energy of ZnO at 400, 600 and 800 ℃ is 4.16±0.08, 4.25±0.11 and 4.05±0.23 eV respectively. Temperature has a remarkable effect on the structure of the surface and the interface of ZnO/α-Al2O3(0001). It is found that the Zn-hexagonal symmetry deflexion does not appear during the adsorption growth of ZnO at 400 ℃, and that the ZnO10-10 is parallel with the 10-10 of the α-Al2O3(0001), which is favorable for forming ZnO film with the Zn-terminated surface. It is observed from simulation that there are two kinds of surface structures in the adsorption of ZnO at 600 ℃: one is the ZnO surface that has the Zn-terminated structure, and whose 10-10 parallels the 10-10 of the substrate surface, and the other is the ZnO10-10 //sapphire 11-10 with the O-terminated surface. The energy barrier of the phase transition between these two different surface structures is about 1.6 eV, and the latter is more stable. Therefore,the suitable temperature for the thin film growth of ZnO on sapphire is about 600 ℃, and it facilitates the formation of wurtzite structure containing Zn-O-Zn-O-Zn-O double-layers as a growth unit-cell. At 600 ℃, the average bond length of Zn-O is 0.190±0.01 nm, and the ELF value indicates that the bond of (substrate)-O-Zn-O has a distinct covalent character, whereas the (Zn)O-Al (substrate) shows a clear character of ionic bond. However, at a temperature of 800 ℃, the dissociation of Al and O atoms on the surface of the α-Al2O3(0001) leads to a disordered surface and interface structure. Thus, the Zn-hexagonal symmetry structure of the ZnO film is not observed under this condition     

Distribution of active earth pressure of retaining wall with wall movement of rotation about top

Based on the Coulomb‘s theory that the earth pressure against the back of a retaining wall is due to the thrust exerted by the sliding wedge of soil from the back of the wall to a plane which passes through the bottom edge of the wall and has an inclination equal to the angle of O, the theoretical answers to the unit earth pressure, the resultant earth pressure and the point of application of the resultant earth pressure on a retaining wall were obtained for the wall movement mode of rotation about top. The comparisons were made among the formula presented here, the formula for the wall movement mode of translation, the Coulomb‘ s formula and some experimental observations. It is demonstrated that the magnitudes of the resultant earth pressures for the wall movement mode of rotation about top is equal to that determined by the formula for the wall movement mode of translation and the Coulomb‘s theory. But the distribution of the earth pressure and the points of application of the resultant earth pressures have significant difference.     

One-dimensional consolidation of layered soils with impeded boundaries under time-dependent loadings

On the basis of Terzaghi‘s one-dimensional consolidation theory, the variation of effective stress ratio in layered saturated soils with impeded boundaries under timedependent loading was studied. By the method of Laplace transform, the solution was presented. Influences of different kinds of cyclic loadings and impeded boundaries conditions were discussed. Through numerical inversion of Laplace transform, useful illustrations were given considering several common time-dependent loadings. Pervious or impervious boundary condition is just the special case of the problem considered here. Compared with average index method, the results from the method illustrated are more accurate.