Sharif Digital Repository

A variational theory (VT), in which the potential energy of a real system is evaluated relative to the hard-sphere system, was used to investigate the medium's effects on the pair potential parameters. By adding the medium's effects to the isolated pair potential, the concept of an 'effective pair potential' (EPP) was introduced. The EPP parameters were compared with those of the average effective pair potential (AEPP) for Ar, which showed the importance of the medium effects and the long range interactions of the AEPP in dense fluids. The study showed that the depth parameter of the AEPP is much larger than that of the EPP  

In this work, we consider each normal alkane as a hypothetical mixture of methyl and methylene groups, in which the interaction potential of each pair is assumed to be the average effective pair potential. Then, the LIR equation of state (EOS) is extended for such a hypothetical mixture. Also, three basic compounds, namely, propane, n-butane and cyclohexane, are used to obtain the contribution of each carbonic group in the EOS parameters. Using the calculated EOS parameters along with the modified EOS, the density of n-alkanes and their mixtures at different pressures and temperatures are calculated. The average percentage error in density is found to be less than 1.5% for both the pure... 

In this paper, we have derived two equations of state, one for the metallic and ionic solids and the other for the remaining solids on the basis of the concept of the average effective pair potential (AEPP). According to the former EOS, (Z-1)υ2 is linear with respect to 1/ρ, where Z is the compressibility factor and υ = 1/ρ is the molar volume for each isotherm. On the basis of the latter EOS, (Z-1)υ2 is a linear function in terms of ρ2 for each isotherm. As these EOSs suggest, the temperature dependencies of the internal energy is separable from its density dependencies. Hence, the heat capacity of a solid is independent of its density, interaction potential parameters and non-ideal thermal... 

In this paper the density and temperature dependencies of surface tension are investigated. Using the Lennard-Jones (12,6), as an effective pair interaction potential, a linear expression is derived for isotherms of γ /ρ 2 versus ρ 2 for some normal and ChloroFluoroCarbons (CFCs) fluids, where is surface tension and ρ = 1/v is molar density. The linearity behavior of the derived equation is well fitted onto the experimental data of surface tension for monatomic, diatomic, nonpolar, polar, hydrogen-bonded and chlorofluorocarbons. In addition, the temperature dependence of surface tension for 20 different fluids is examined, in which the contributions of both terms of the average effective... 

The concept of effective pair potential (EPP), in which medium effects and contribution of long-range interactions are added to near-neighbor pair interactions, is a useful tool to derive and calculate the thermodynamic quantities. It has been shown that the extended Lennard-Jones (12, 6, 3) potential is an accurate EPP for many systems. However, the parameters of this EPP are not known for any systems. We introduce a new approach to use experimental pvT data of a fluid to calculate its EPP parameters. Such calculation has been carried out for some fluids at some temperatures. Unlike the isolated pair potential, it has been shown that the parameters significantly vary with temperature. We... 

In the present work, the thermodynamic of dense fluids, both compressed liquids and dense supercritical fluids, has been modeled, solely, based on the contribution of attraction of effective pair potential. The intermolecular interaction is modeled by the hard-core Yukawa potential (HCY) as an effective pair potential (EPP) with temperature dependent hard-core diameter. Using this EPP in the exact thermodynamic relations, an equation of state (EoS) for the compressibility factor of dense fluid has been derived. This EoS shows that (Z - ZCS) as function of ρ1/3 must be linear for each isotherm of fluid where ZCS is the compressibility factor of the reference fluid (Carnahan-Starling (CS) EoS)... 

In the present work, several new thermodynamic linear isotherm regularities for the dense fluids have been derived for the first time. For this purpose, the thermodynamic perturbation theory (TPT) employing only the attractive effective pair potential (AEPP) as u(r) = - ϵeff (σeff / r)m was used, where σeff which is the effective hard core diameter, is temperature dependent and m > 0. Based on the derived regularities, the isotherm (Z - Z(0))v2 is a linear function of ρ2, ρ and 1/ρ, depends on the values of m = 12, 9 and 6, respectively where Z - Z(0) is the difference between the experimental compressibility factor of the real fluid (Z) and that of the reference fluid (Z(0)). Also, Z - Z(0)... 

Water inside carbon nanotubes as an example of nanoconfined water has gained noticeable attention, in both theoretical and applied aspects. Molecular simulation has played a major role in the studies in this field. Yet, there is a need for systematic study of simulation results and compilation of scientifically reliable predictive relations. Here we present Monte Carlo simulations of water inside carbon nanotubes with different radii. An equation of state which was derived on the basis of the extended Lennard-Jones (12,6,3) as the effective pair potential is chosen for the system of water inside the carbon nanotubes. The equation of state is modified to take the effects of anisotropic... 

A general regularity was found based on an effective pair potential of Lennard-Jones LJ (12, 6), for both dense, nonmetallic and nonionic fluids and solids according to which (Z-1) v2 linearly varies with respect to ρ2 for each isotherm, and this equation of state (EoS I) is known as LIR. However, despite the fact that Ne is a simple spherical species, unexpectedly, its solid and liquid phases both show a significant deviation from EoS I. In this work, we have investigated the accuracy of the EoS I for other systems, including quantum light molecules, such as D 2, H 2 and He, in both fluid and solid states at different temperatures. Like Ne, we have noticed that these systems do not well...