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**Search for:**effective-pair-potentials

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#### Investigation of the temperature and density dependences of the effective pair potential parameters using variational theory

, Article International Journal of Thermophysics ; Volume 25, Issue 1 , 2004 , Pages 187-203 ; 0195928X (ISSN) ; Parsafar, G. A ; Mansoori, G. A ; Sharif University of Technology
Kluwer Academic/Plenum Publishers
2004

Abstract

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

#### Extension of linear isotherm regularity to long chain alkanes

, Article Iranian Journal of Chemistry and Chemical Engineering ; Volume 22, Issue 2 , 2003 , Pages 1-8 ; 10219986 (ISSN) ; Kalantar, Z ; Sharif University of Technology
2003

Abstract

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...

#### Deriving linear isotherms for solids

, Article Fluid Phase Equilibria ; Volume 271, Issue 1-2 , 2008 , Pages 94-102 ; 03783812 (ISSN) ; Parsafar, G. A ; Dinpajooh, M ; Sharif University of Technology
2008

Abstract

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...

#### Calculation of Effective Pair Potential Function by Using Pressure−Temperature−Volume Data

, M.Sc. Thesis Sharif University of Technology ; Parsafar, Gholamabbas (Supervisor)
Abstract

In this work, by considering the medium effects and adding the long−range interactions to the isolated pair potential, the concept of the extended effective pair potential of the Lennard−Jones (12, 6, 3) has been purposed for dense systems. Due to lack of any information regarding the parameters of this potential for any fluid, the purpose of this work is to introduce a new method to calculate these parameters using experimental pVT data. Since the extended potential of Lennard− Jones (12, 6, 3) is a general function based on which that an equation of state can be derived (equation of state III) predicts many properties of dense systems that no deviation is observed. Also it doesn’t have...

#### Density and temperature dependencies of liquid surface tension

, Article Iranian Journal of Chemistry and Chemical Engineering ; Volume 30, Issue 2 , 2011 , Pages 79-90 ; 10219986 (ISSN) ; Parsafar, G. A ; Akbarzadeh, H ; Sharif University of Technology
2011

Abstract

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...

#### Calculation of effective pair potential via the volumetric data

, Article Phase Transitions ; Vol. 87, issue. 1 , 2014 , pp. 38-58 ; ISSN: 01411594 ; Parsafar, G ; Sharif University of Technology
Abstract

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...

#### Linear yukawa isotherm regularity for dense fluids derived based on the perturbation theory

, Article Fluid Phase Equilibria ; Volume 409 , 2016 , Pages 105-112 ; 03783812 (ISSN) ; Farrokhpour, H ; Parsafar, G. A ; Sharif University of Technology
Elsevier
2016

Abstract

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)...

#### Towards new thermodynamic regularities for dense fluids based on the effective attraction pair potential via the perturbation theory

, Article Journal of Molecular Liquids ; Volume 220 , 2016 , Pages 623-630 ; 01677322 (ISSN) ; Farrokhpour, H ; Parsafar, G. A ; Sharif University of Technology
Elsevier B.V
2016

Abstract

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)...

#### Toward an equation of state for water inside carbon nanotubes

, Article Journal of Physical Chemistry B ; Volume 116, Issue 16 , April , 2012 , Pages 4943-4951 ; 15206106 (ISSN) ; Parsafar, G. A ; Sharif University of Technology
American Chemical Society
2012

Abstract

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...

#### Influence of quantum effect on deviation from linear isotherm regularity

, Article Scientia Iranica ; Volume 19, Issue 3 , June , 2012 , Pages 555-560 ; 10263098 (ISSN) ; Parsafar, G. A ; Sharif University of Technology
2012

Abstract

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...