Simulation Of Thermodynamic Properties Research Articles

Molecular Dynamics Simulation of Thermodynamic Properties for Al-Si Alloys in Material Manufacturing Engineering

The molecular dynamics method was used to simulate thermodynamic properties of two binary alloys: Al75 Si25, Al85 Si15..They were calculated of the energy functions, including cohesive energy , formation energy. Results display, formation energy and excess free energy are all negative values, so Al-Si alloys belong to negative system. The atomic interactions were analyzed in macroscopic and microcosmic views. The calculated formation energy can describe the deviation degree between the actual alloy and the ideal melt quantitatively.

A molecular dynamics simulation of thermodynamic properties of undercooled liquid Ni2TiAl alloy

Base on the embedded-atom method，the enthalpy and the density of Ni2TiAl alloy are calculated by using molecular dynamics simulations.The temperature dependence of the specific heat of normal and undercooled liquid Ni2TiAl alloy is obtained.The results indicate that the specific heat and the density increase linearly with the decrease of temperature，and the Neumann-Kopp rule can be applied to estimate the specific heat of undercooled liquid Ni2TiAl alloy. Meanwhile, the size effect in the simulation domain is indicated to be negligible.

Statistical substantiation of the van der Waals theory of inhomogeneous fluids.

Computer experiments on simulation of thermodynamic properties and structural characteristics of a Lennard-Jones fluid in one- and two-phase models have been performed for the purpose of checking the base concepts of the van der Waals theory. Calculations have been performed by the method of molecular dynamics at cutoff radii of the intermolecular potential r(c,1)=2.6sigma and r(c,2)=6.78sigma. The phase equilibrium parameters, surface tension, and density distribution have been determined in a two-phase model with a flat liquid-vapor interface. The strong dependence of these properties on the value of r(c) is shown. The p,rho,T properties and correlation functions have been calculated in a homogeneous model for a stable and a metastable fluid. An equation of state for a Lennard-Jones fluid describing stable, metastable, and labile regions has been built. It is shown that at T > or =1.1 the properties of a flat interface within the computer experimental error can be described by the van der Waals square-gradient theory with an influence parameter kappa independent of the density. Taking into account the density dependence of kappa through the second moment of the direct correlation function will deteriorate the agreement of the theory with data of computer simulation. The contribution of terms of a higher order than (nablarho)(2) to the Helmholtz free energy of an inhomogeneous system has been considered. It is shown that taking into account terms proportional to (nablarho)(4) leaves no way of obtaining agreement between the theory and simulation data, while taking into consideration of terms proportional to (nablarho)(6) makes it possible to describe with adequate accuracy all the properties of a flat interface in the temperature range from the triple to the critical point.

Monte Carlo simulation of thermodynamic properties for two-dimensional Lennard-Jones fluids

Canonical ensemble Monte Carlo simulations have been carried out to investigate the thermodynamic properties of two-dimensional fluids subjected to truncated Lennard-Jones 12-6 potential. The simulations of thermodynamic states sweep across liquid-vapor regime over a wide range of thermodynamic conditions. Simulated isotherms behave van der Waals loop-like characteristics in the liquid-vapor phase-transition region. It suggests a continuous isothermal phase transition in the case of micro system, in which the system size prohibits phase separation. Two-dimensional dimensionless van der Waals equation of states has been obtained from theoretical analysis. By fitting simulated data to this equation, temperature-dependent parameters in the equation have been determined.

Ab initiointermolecular potentials of methane, nitrogen and methane + nitrogen and their use in Monte Carlo simulations of fluids and fluid mixtures

Intermolecular pair potentials of methane and of methane + nitrogen have been calculated by quantum chemical ab initio methods. The repulsive and electrostatic parts were determined pointwise for various distances and orientations of the dimers (supermolecule approach) by self-consistent field (SCF) calculations including the counterpoise correction. Gaussian basis functions of triple-zeta quality plus one set of polarization functions on all atoms were used. The dispersion energy, which cannot be calculated at the SCF level, has been added by a semi-empirical estimate. These potentials and the pair potential for nitrogen (of similar quality, taken from the literature) were fitted to analytical functions and used for NVT Monte Carlo simulations of thermodynamic properties of the fluids and their mixture over a wide temperature/density area. Comparison with measurements and with Monte Carlo results from the literature (pressure, internal energy, radial distribution function) obtained with other pair potent...

A computer simulation of thermodynamic properties of solid Na

The recently derived pseudopotential of Rasolt and Taylor (1970, 1975) has been used to carry out a computer simulation of the properties of solid Na near its melting point. The authors have calculated the elastic constants, the thermodynamic Gruneisen parameter, the pressure, the specific heat and the quantity (dp/dT)v at both 293K and 361K. The calculation was performed for molar volumes that correspond roughly to those observed experimentally at zero pressure. A system composed of 250 particles is used, in which each atom is allowed to interact with its nearest 112 neighbours; periodic boundary conditions have been introduced to allow for the simulation of an infinite system. The overall agreement of the calculations with experimental data is good when one makes allowance for possible contributions from the electron gas terms. However, the shear constant c44, which contains no such contributing terms, is definitely smaller than the experimental values of Fritsch, Geipel and Prasetyo (1973). This may indicate an inadequacy of the pseudopotential.