Structural model for vitrification of pure metals

The model of iron with Pak-Doyama pair interatomic potential was used as an example to demonstrate by molecular dynamic calculations that the structural stabilization of an amorphous phase of pure metals is due to the formation of a percolation cluster composed of the interpenetrating and mutually contacting icosahedra whose vertices and centers are occupied by atoms.     

Molecular dynamics of liquid lead near its melting point

The molecular dynamics of liquid lead is simulated at T = 613 K using the following three models of an interparticle interaction potential: the Dzugutov pair potential and two multiparticle potentials (the “glue” potential and the Gupta potential). One of the purposes of this work is to determine the optimal model potential of the interatomic interaction in liquid lead. The calculated structural static and dynamic characteristics are compared with the experimental data on X-ray and neutron scattering. On the whole, all three model potentials adequately reproduce the experimental data. The calculations using the Dzugutov pair potential are found to reproduce the structural properties and dynamics of liquid lead on the nanoscale best of all. The role of a multiparticle contribution to the glue and Gupta potentials is studied, and its effect on the dynamic properties of liquid lead in nanoregions is revealed. In particular, the neglect of this contribution is shown to noticeably decrease the acoustic-mode frequency.     

Unified study and transport properties of simple metals

The resistivity, thermoelectric power at the melting points and temperature variation of resistivity of the liquid alkali metals are studied with local Heine-Abarenkov and the modified Ashcroft pseudopotentials. The parameters of the model potentials are obtained from a unified study of the static and dynamic properties of the metals. The effect of different dielectric function and structure factor on the transport properties is discussed. It is shown that the simple modified Ashcroft pseudopotential reproduces the result fairly well except for Li and Cs.     

Self-consistent Shaw optimized model potential: Application to the determination of structural and atomic transport properties of liquid alkali metals by molecular dynamics simulations

The ‘first-principles’ fully non-local and energy-dependent optimized model potential (OMP) derived by Shaw is developed further. In contrast to Shaw's original paper, OMP parameters are derived in a self-consistent manner that does not rely on knowledge of experimental values of the ionization and cohesive energies. To our knowledge, this is the first time that this method has been used for effective potential calculations. In an application to liquid Li, Na, and K alkali metals, we used OMP pseudopotential-based interactions between ions to carry out standard molecular dynamics simulations. In the calculations, the ionic structure for the liquid state was first checked at a temperature near the melting point. Similar accurate calculations, but for atomic transport properties, predict the temperature dependence of the self-diffusion coefficients. The theoretical results obtained are in overall agreement with available experimental measurements. Thus, one can have some confidence in the ability of the optimized model potential to give a good representation of the physical properties of these alkali ions in the liquid environment.     

New pair potentials from an improved born-green integral equation: Application to liquid metals

With an improvement of the superposition approximation in the Born-Green integral equation recently proposed an attempt is made to extract new effective pair potentials from structure factors of simple liquids. The improvement is obtained by taking the first three terms of a hard-core density expansion of the triplet correlation function. The method of calculation is based on the solution of the integral equation in k-space. It is shown that the resulting potential of the improved Born-Green equation from a hard-core structure factor actually is hard-core like contrary to the Born-Green result. From measured structure factors of some simple liquid metals (Na-100°C, Al-670°C and Ni-1600°C) pair potentials are determined. With this application a significant improvement over the Born-Green theory can be achieved. In comparison to the old discrepancy between the Born-Green equation and theoretical models the results agree very well with theoretical calculations in the repulsive range of the potential.     

Analysis of semi-empirical interatomic potentials appropriate for simulation of crystalline and liquid Al and Cu

We investigate the application of embedded atom method (EAM) interatomic potentials in the study of crystallization kinetics from deeply undercooled melts, focusing on the fcc metals Al and Cu. For this application, it is important that the EAM potential accurately reproduces melting properties and liquid structure, in addition to the crystalline properties most commonly fit in its development. To test the accuracy of previously published EAM potentials and to guide the development of new potential in this work, first-principles calculations have been performed and new experimental measurements of the Al and Cu liquid structure factors have been undertaken by X-ray diffraction. We demonstrate that the previously published EAM potentials predict a liquid structure that is too strongly ordered relative to measured diffraction data. We develop new EAM potentials for Al and Cu to improve the agreement with the first-principles and measured liquid diffraction data. Furthermore, we calculate liquid-phase diffusivities and find that this quantity correlates well with the liquid structure. Finally, we perform molecular dynamics simulations of crystal nucleation from the melt during quenching at constant cooling rate. We find that EAM potentials, which predict the same zero-temperature crystal properties but different liquid structures, can lead to quite different crystallization kinetics. More interestingly, we find that two potentials predicting very similar equilibrium solid and liquid properties can still produce very different crystallization kinetics under far-from-equilibrium conditions characteristic of the rapid quenching simulations employed here.     

Molecular dynamics of liquid alkaline-earth metals near the melting point

Results of the studies of the properties like binding energy, the pair distribution function g(r), the structure factor S(q), specific heat at constant volume, velocity autocorrelation function (VACF), radial distribution function, self-diffusion coefficient and coordination number of alkaline-earth metals (Be, Mg, Ca, Sr and Ba) near melting point using molecular dynamics (MD) simulation technique using a pseudopotential proposed by us are presented in this article. Good agreement with the experiment is achieved for the binding energy, pair distribution function and structure factor, and these results compare favourably with the results obtained by other such calculations, showing the transferability of the pseudopotential used from solid to liquid environment in the case of alkaline-earth metals.     

A new scheme for calculation of effective pair potentials for liquid metals

A new scheme based on the Singwi et al. theory for an interacting electron gas is proposed for calculating pair potentials for liquid metals and applied to liquid sodium and rubidium. The resulting pair potentials are in much better agreement with the pseudopotential calculations than any of the three usual approximations, PY, HNC or BG used in the literature.     

Structure of liquid Al and Al67Mg33 alloy: comparison between experiment and simulation

We report data on the structure of liquid Al and an Al₆₇Mg₃₃ alloy obtained from state-of-the-art X-ray diffraction experiments and ab initio molecular dynamics (AIMD) simulations. To facilitate a direct comparison between these data, we develop a method to elongate the AIMD pair correlation function in order to obtain reliable AIMD structure factors. The comparison reveals an appreciable level of discrepancy between experimental and AIMD liquid structures, with the latter being consistently more ordered than the former at the same temperature. The discrepancy noted in this study is estimated to have significant implications for simulation-based calculations of liquid transport properties and solid–liquid interface kinetic properties.     

FCC金属空位的MAEAM理论研究

应用涉及更远邻原子的改进分析型嵌入原子方法（MAEAM）计算了面心立方（fcc）金属（Ag,Al,Au,Cu,Ir,Ni,Pd,Pt,Rh）的空位性能。在MAEAM计算中,考虑了远邻原子相互作用和单空位迁移能,对两体势进行了坚挺处理,并采用新的截尾函数和加强光滑连接条件对两体势作了截尾处理。同时为了更好的符合面心立方晶体的结合能、弹性常数和平衡条件,调整了多体势的模型常数。未弛豫空位性能计算中考虑了两体势的截尾距离和电子密度分布函数的截尾距离之间近邻原子的作用以及双空位迁移途径周围的原子非对称分布。结果与其它方法计算结果基本一致,但更加接近实验值。对双空位迁移能的计算结果有利地说明了fcc金属双空位5种迁移途径的扩散机制。     

Electrical resistivity of alkali metals

The temperature variations of the electrical resistivity of alkali metals lithium, sodium, potassium, rubidium and caesium are calculated in the free electron approximation and using Krebs's model for the phonon spectrum. The double average over the Fermi surface is evaluated by an improved method due toBailyn and the separation between normal and Umklapp processes is affected in a more satisfactory manner. The results of the calculations are compared with the experimental data obtained at different temperatures. The theoretical resistivity curves for sodium, potassium, rubidium and caesium show satisfactory agreement with experiment, but not in the case of lithium.     

Structure of molten silicon and germanium by X-ray diffraction

X-ray diffraction patterns have been obtained from molten silicon and germanium near the melting point. In both cases the structure factor was a low first peak maximum with a small hump on its high angle side in contrast with those of simple molten metals such as sodium and aluminum. It was also found that the pair correlation functions for these molten elements are characterized by a low peak maximum which follows the usual first peak maximum corresponding to the nearest neighbour distance. The electrical resistivity and thermoelectric power have been calculated on the Ziman theory using thet-matrix of muffin-tin potential based on the structural data observed in this work. Good agreement was found in most cases.     

Structure of some liquid transition metals using integral equation theory

We present the results of calculations of the structure factorS(q) of some liquid 3d transition metals using the self consistent hybridized mean spherical approximation (HMSA) integral equation. The local pseudopotential used is composed of the empty core model and a part that takes care of s-d mixing through an inverse scattering approach to model the interionic pair potential. The results presented are in very good agreement with experiment for most of the systems investigated near freezing, as well as for the noble metals Cu, Ag and Au, thus, confirming the reliability of the pseudopotential in the present integral equation scheme.     

Electrons in non-crystalline metals —Still a challenging problem

The following aspects of the electronic properties of liquid and amorphous metals are studied: (i) density of states of polyvalent liquid metals by means of finite cluster calculations, (ii) the Hall coefficient of simple metals by the use of a generalised transport equation, (iii) the effect of multiple scattering on the electrical resistivity.Dedicated to Professor Harry Thomas on the occasion of his 60th birthday     

Triplet correlation and pair potential functions in liquid neon and sodium

Recent neutron diffraction data for liquid neon and X-ray diffraction data for liquid sodium have been analyzed with the purpose of studying the triplet correlation function in these liquids by means of the method suggested by Egelstaff, Page and Heard. In both cases, it was found that the function H(Q) which expresses the deviation from the superposition approximation indicates the deviation from zero and the effect of the pressure derivative of the structure factor to the function H(Q) is little. Besides, the pair potentials have been investigated from these diffraction data at various pressures using the Born-Green equation. The pair potential functions obtained for three states of liquid neon are the Lennard-Jones type, whereas those obtained for liquid sodium with a provisional assumption based on the experimental data are of the long-range oscillatory type. The pair potentials obtained in this work are useful for the interpretation on the difference in the pressure dependence of the structure factor for liquid neon and sodium.     

Electrical resistivity of alkali metals: Inflation–deflation effect of Fermi surface

The electrical resistivity of liquid alkali metals was calculated using the extended Ziman formula. The possible role of Fermi surface (FS) inflation–deflation (ID) was examined. The calculations reveal that replacing the sharp free electron FS by the expanded (respectively, contracted) one substantially improves the results. This was achieved directly by considering a FS correction factor of the Fermi radius and indirectly by a shift in the muffin-tin zero (MTZ) of the potential from its initial values. Consequently, a correlation between the shift of the MTZ of the potential and the FS factor parameter is revealed. The role of this correlation might contribute to a better understanding of the electron transport properties of other liquid metals and their alloys.     

Strongly correlated quantum spin liquid in herbertsmithite

Strongly correlated Fermi systems are among the most intriguing and fundamental systems in physics. We show that the herbertsmithite ZnCu₃(OH)₆Cl₂ can be regarded as a new type of strongly correlated electrical insulator that possesses properties of heavy-fermion metals with one exception: it resists the flow of electric charge. We demonstrate that herbertsmithite’s low-temperature properties are defined by a strongly correlated quantum spin liquid made with hypothetic particles such as fermionic spinons that carry spin 1/2 and no charge. Our calculations of its thermodynamic and relaxation properties are in good agreement with recent experimental facts and allow us to reveal their scaling behavior, which strongly resembles that observed in heavy-fermion metals. Analysis of the dynamic magnetic susceptibility of strongly correlated Fermi systems suggests that there exist at least two types of its scaling.     

Application of a structure factor-potential relationship to the electrical resistivity of the liquid alkali metals

In the Ziman formulation for the electrical properties of liquid metals, the resistivity depends on an average of the product of the structure factor and the pseudopotential. Ascarelli, Harrison and Paskin have derived a relationship for small wave vector between the structure factor and the pseudopotential for liquid metals such as the alkali metals. This formulation has been used over the entire range of wave vector (k = 0 to 2k _F). The resistivities of Na, K, Rb and Cs calculated with no adjustable parameters are within 25% of the observed values, while Li is underestimated by about a factor of five. The temperature dependencies of all but Li (which is anomalously non-linear) are in similar agreement with experiments made at constant volume.