Triplet correlation function and related quantities in liquid sodium from experimental structure factor

Recent X-ray diffraction data for liquid sodium under pressure have been analyzed for the purpose of studying the triplet correlation function by means of the method proposed by Egelstaff, Page and Heard. Besides, the pair correlation function and pair potential have been calculated from these diffraction data at various pressures using the common Fourier Analysis and the Born-Green equation. The relation between the pair, triplet correlation functions and the pair potential and the various changes of the structure factor by pressure was investigated.     

紧束缚势和修正的嵌入原子势计算液态Sn双体相关函数差异

对500个Sn原子分别用两种模型(紧束缚势和修正的嵌入原子势)计算了400℃～1700℃温度范围内纯Sn的双体相关函数g(r).将计算结果与实验数据进行了对比分析,发现两种计算结果都能基本上反映液态Sn的结构及其随温度的变化情况:原子最近邻距离与实验结果相近;随着温度降低,双体相关函数第一峰变得尖锐,第二峰变得明朗.修正的嵌入原子势模型得到的双体相关函数的第一峰右侧有个突起的肩膀,这在实验结果中也被发现,而紧束缚势模型得到的双体分布函数肩膀不明显.     

紧束缚势和修正的嵌入原子势计算液态Sn双体相关函数差异

对500个Sn原子分别用两种模型（紧束缚势和修正的嵌入原子势）计算了400℃~1700℃温度范围内纯Sn的双体相关函数g（r）。将计算结果与实验数据进行了对比分析,发现两种计算结果都能基本上反映液态Sn的结构及其随温度的变化情况：原子最近邻距离与实验结果相近;随着温度降低,双体相关函数第一峰变得尖锐,第二峰变得明朗。修正的嵌入原子势模型得到的双体相关函数的第一峰右侧有个突起的肩膀,这在实验结果中也被发现,而紧束缚势模型得到的双体分布函数肩膀不明显。     

Non-polar solute-water pair correlation functions

The microscopic theory of the solvation of non-polar solutes in water proposed by Pratt and Chandler has been generalized in order to obtain separate solute-oxygen and solute-hydrogen radial distribution functions, g(r). The g(r)s predicted by this method for a spherical solute have been tested by comparison with the corresponding functions from two computer simulation studies. The water-water interactions were described by the configuration intereaction potential (CI) in both cases. The agreement between theoretical and simulation results is good for the solute-oxygen g(r), less so for the solute-hydrogen function. Moreover, the influence of the model of water on the calculated solute-solvent g(r)s has been examined by comparing results obtained with partial structure functions derived from the CI model and from recent neutron diffraction measurements. It is found that CI model and real water yield remarkably different solute-water radial distribution functions. Finally, the solvation of a model two-site solute has been studied for various bond lengths and the results confirm that when the space between the sites is sufficient to host a water molecule, the solvation of each site is the same as that of an isolated site, with respect to oxygen as well as hydrogen.     

Inverse Monte Carlo study on effective interaction potential of Ag--Rh alloy from pair correlation functions

This paper presents an inverse Monte Carlo method to reconstruct pair interaction potential from pair correlation function. This approach adopts an iterative algorithm on interaction potential to fit known pair correlation function by compelling deviations of canonical average to meet with Hamiltonian parameters on a basis of statistical mechanism. The effective interaction potential between particles in liquid Ag--Rh alloys has been calculated with the inverse Monte Carlo method. It demonstrates an effective and simple way to obtain the effective potential of complex melt systems.     

The direct pair correlation function of liquid indium

The static structure factor S(k) of liquid indium has been measured accurately down to $\text{k = 0.8}\text{A}\text{?}{}^{\mathrm{?1}}$ using CuKα radiation with reflection geometry. The direct pair correlation function in k space is analyzed to demonstrate the utility of this technique in reducing errors in the resulting direct pair correlation function in configuration space.     

Comparison of structure factors and pair correlation functions obtained using coulomb attractive potential and screened coulomb potential for the suspended macroions

The structure factors and pair correlation functions have been calculated for the macroions suspended in water using coulomb attractive potential (CAP) and the results have been compared well with the results obtained from the RMSA and MMSA using screened coulomb potential (SCP). Differences among the values of compressibility in the limit of zero momentum transfer, excess energy per macroion and coordination number for both the potentials have been reported. Liquid like ordering of the FCC type has been obtained using both CAP as well as SCP potentials between suspended macroions.     

Ab initio potential energy curve for the neon atom pair and thermophysical properties for the dilute neon gas. II. Thermophysical properties for low-density neon

A neon–neon interatomic potential energy curve determined from quantum-mechanical ab initio calculations and described with an analytical representation (R. Hellmann, E. Bich, and E. Vogel, Molec. Phys. 106, 133 (2008)) was used in the framework of the quantum-statistical mechanics and of the corresponding kinetic theory to calculate the most important thermophysical properties of neon governed by two-body and three-body interactions. The second and third pressure virial coefficients as well as the viscosity and thermal conductivity coefficients, the last two in the so-called limit of zero density, were calculated for natural Ne from 25 to 10,000 K. Comparison of the calculated viscosity and thermal conductivity with the most accurate experimental data at ambient temperature shows that these values are accurate enough to be applied as standard values for the complete temperature range of the calculations characterized by an uncertainty of about ±0.1% except at the lowest temperatures.     

A relation between structure and pair potential for liquid metals

We emphasize the importance of considering the relationship between the structure of a liquid and the interatomic potential directly from the point of view of wave vector space (k space). Although the Ornstein-Zernike equation was not originally derived from this point of view, this equation when transformed into the k-space representation has direct physical content, when coupled with a normal mode representation according to the approaches of Pines and Bohm (1952), and Percus and Yevick (1958). These normal modes are defined isothermally, and the relation to the dynamical modes of the liquid is discussed. The use of a simple k-space relationship between the transform of the Ornstein-Zernike direct correlation function and the transform, V_k , of the interatomic potential is explored. This leads to a correspondingly simple relationship between the structure factor and the interatomic potential. It is equivalent to a generalized Debye-Hückel equation and is expected to be valid only under special circumstances; namely, where the potential is long range in a particular sense and the small k behaviour of V_k is dependent mainly upon this long-range behaviour and relatively insensitive to details of the potential at short distances. It is noted that these conditions appear to be met reasonably well for the liquid alkali metals. The comparison of theory and experiment is somewhat uncertain because of incomplete experimental data on the structure factor as well as unresolved theoretical issues.     

The orientational pair correlation functions in a dense hard sphere fluid at long times

The two-particle contribution to the potential part of the stress tensor autocorrelation function of a dense hard sphere fluid is studied. It is shown that the long-time decay is given as the solution of a diffusion equation for the relative particle in a potential of mean force. The diffusion constant needed in order to accurately reproduce molecular dynamics results is found to be somewhat lower than the self-diffusion constant.