Sharif Digital Repository

We present in this paper a general analytical solution to the integral equations of liquid state theories (Born-Green-Yvon, hyper-netted-chain, and Percus-Yevick Equations) at low-density limit for potentials with a hard core. For the specific case of the Lennard-Jones potential with a hard core, we have derived an analytical function for the radial distribution function at high temperature and low density. We have noted that this function has two humps which is the characteristic feature of the radial distribution function at low densities. In addition, this function has been used to calculate the third virial coefficient for such a fluid exactly. We see that for the especial case of... 

A new potential function, which can in a simple and reasonable manner represent the molecular interaction of many kinds of hard-core fluids by varying the value of its parameter, is proposed. For prediction of thermodynamic properties of hard-core fluids such as the square-well (SW) and hard core Lennard-Jones (HCLJ), a simple perturbed equation of state (EOS) is derived by using the new potential function along with the Barker-Henderson perturbation theory. This method yields a simple and general analytical expression for each thermodynamic property of such fluids. The most important feature of these expressions is that they have no adjustable parameter and in some regions in which there is... 

Two new hard-sphere EOS are proposed and tested using the same attractive potential terms used by the SAFT EOS. Generalized expressions for the pair RDF at contact value, the compressibility factor, and the excess chemical potentials have been derived. Extension to mixtures is tested using three mixing rules for multicomponent hard-sphere fluids. The proposed EOS combined with the Santos et al. and the Barrio-Solana mixing rules reproduced the compressibility factors and the excess chemical potentials more accurately than the Boublik-Mansoori-Carnahan-Starling-Leland (BMCSL) EOS. However the pair RDF at contact value had larger deviations than those obtained with the BMCSL EOS. The... 

Synthesis and characterization of metal dithiocarbamate complexes of N 1 ,N 3 -dicinnamylpropane-1,3-diamine, N 1 ,N 4 -dicinnamylbutane-1,4-diamine and N 1 ,N 6 -dicinnamylhexane-1,6-diamine are reported. The ligands are prepared using cinnamaldehyde and primary diamines to provide the corresponding diimines, followed by reduction with NaBH 4 to afford the corresponding secondary diamines. Diamines react with carbon disulfide in basic medium to furnish the corresponding bis(dithiocarbamate) salts, which underwent complexation with metals. The prepared complexes were characterized by IR, 1 H and 13 C NMR, TGA and elemental analyses. Although the dinuclear metal dithiocarbamate macrocyclic... 

The extent of the self-association of water in supercritical CO2 has been investigated in a wide range of density and temperature by the test particle insertion technique. The results show that the association constant for water decreases with temperature and weakly depends on CO2 density. This weak density dependence provides evidence for the lack of a strong specific CO2-water interaction. Comparing calculated association constants with its gas-phase values shows that the association constant is at most ca. 38% lower than its gas-phase value in the high density-low temperature region. Inspection of the simulated radial distribution functions revealed that forming modest water-CO2 complexes... 

Based on a new derived radial distribution function (RDF) for potentials with a hard-core we have presented in this paper a method to apply the derived RDF for calculating thermodynamic properties of real fluids up to moderate densities. In order to use the derived RDF for real fluids, one of the potential parameters is chosen in such a way that the RDF behaves more like that for a real fluid. Hence we have been able to calculate all thermodynamic properties of a simple fluid analytically. We have then applied our procedure to a Lennard-Jones fluid and compared the results with simulation data. The agreement is good up to moderate densities, i.e. ρ* ≤ 0.6, which lies in the liquid range of... 

In this paper, we present a novel wall boundary condition model, which stands just on the physical facts, for the dissipative particle dynamics (DPD) method. After the validation of this model by means of the common benchmarks such as the Couette and the Poiseuille flows, we study the effects of this model on the diffusion coefficient in a wide variety of different coarse-graining levels. The obtained results show that the proposed model preserves the thermodynamics of the system, also eliminates the spurious effects of the wall, and consequently is able to preserve the accurate structural characteristics of the working DPD fluid in the wall's vicinity. We also study the fluid flow through a... 

Using a general expression for the second term in the density expansion of the hard core potentials, we obtained an analytical expression for the direct correlation function of the hard core double Yukawa potential. The results of this calculation using the proposed direct correlation function and its related radial distribution function through the Ornstein-Zernike equation show good agreements with those obtained by the computer simulation of the same model  

Water molecules are one of the important molecules in nanofluidics. Its structure and its behavior can change with Temperature and cut-off distance parameters. In this study temperature and cut-off distance effects on the nano-scale water molecules behavior are investigated by molecular dynamics simulations. Many water molecular models have been developed in order to help discover the structure of water molecules. In this study, the flexible three centered (TIP3P-C) water potential is used to model the inter- and intramolecular interactions of the water molecules. In this simulation, we have been studied 512 water molecules with periodic boundary conditions and in a simulation box with 25... 

Gold (Au) nanoparticles are widely used in diagnosing cancer, imaging, and identification of therapeutic methods due to their particular quantum characteristics. This research presents different types of aqueous models and potentials used in TIP3P, to study the effect of the particle size and density of Au clusters in aquatic environments; so it can be useful to facilitate future investigation of the interaction of proteins with Au nanoparticles. The EAM potential is used to model the structure of gold clusters. It is observed that in the systems with identical gold/water density and different cluster radii, gold particles are distributed in aqueous environment almost identically. Thus, Au... 

In this paper, the pyrrolic nitrogen functional group's presence is investigated in the selective adsorption of CO2. The grand canonical Monte Carlo (GCMC), molecular dynamics (MD), and density functional theory (DFT) were used for this study's goal. GCMC was used to calculate adsorption isotherms, selectivity, and isosteric heats. MD was used to calculate the radial distribution function (RDF) and diffusion. Reactivity parameters, electrostatic potential (ESP), reduced density gradient (RDG), and independent gradient model (IGM) were calculated using DFT. Adsorption isotherms, selectivity, and isosteric heats demonstrated that the NH group caused the selective adsorption of CO2 among CH4,... 

In this work, molecular dynamic simulation of the mixture of imidazolium based ionic liquids with alcohols is implemented in order to investigate mixing excess properties and some structural and physical properties of the mixture. Excess volumes and enthalpies are evaluated for 11 different mole fractions of ionic liquids at each 0.1, in the range of 0 to 1. Radial distribution function, cohesive energy density, potential of mean force, solvation energy, and diffusion coefficient are reported and analysed. The effects of the cationic alkyl chain length, in comparison with changes of the anions, on these properties are reported. Results reveal that the methanol molecule participates with its... 

A molecular dynamics simulation study has been performed to investigate the solidification and remelting of aluminum using Sutton-Chen many body potential. Different numbers of atoms from 108 to 2048 atoms were considered to find an adequate size for the system. Three different cooling and heating rates, i.e. 10 12 K/s, 10 13 K/s and 10 14 K/s, were used. The structure of the system was examined using radial distribution function. The melting and crystallization temperatures of aluminum were evaluated by calculating the variation of heat capacity during the phase transformation. Additionally, Wendt-Abraham parameters were calculated to determine the glass transition temperature. It is shown... 

Atomistic simulation was used to study the deformation and fracture mechanisms of Ni-Si interfaces under tensile and shear loads dependent on the crystal structure of interface zone. Modified embedded atom method (MEAM) potential was utilized for molecular dynamics (MD) modeling. The simulation includes analysis of common neighbors, coordination number, least-square atomic local strain, and radial distribution function. The profound effect of interface crystallography on the tensile and shear deformation is shown. The highest tensile strength is obtained for interfaces with high plane density due to lowest atomic disorder while under shear loading planes with low density exhibit a high local... 

Abstract High ductility of metals as well as high strength of ceramics has made the metal/ceramic composites an attractive material for many applications requiring high strength to weight ratios. An important issue in using this material is the behavior of the material and its ceramic-metal interface under various loading, especially at high strain rate. To provide a better understanding of the interface conditions, in this work, a molecular dynamics study of the interface behavior in Al/α-Al2O3 composite as the result of tensile and shear loadings is presented. For this purpose, the reactive force field (ReaxFF) potential function is utilized. The effects of... 

Packing of cubic particles arises in a variety of problems, ranging from biological materials to colloids and the fabrication of new types of porous materials with controlled morphology. The properties of such packings may also be relevant to problems involving suspensions of cubic zeolites, precipitation of salt crystals during CO2 sequestration in rock, and intrusion of fresh water in aquifers by saline water. Not much is known, however, about the structure and statistical descriptors of such packings. We present a detailed simulation and microstructural characterization of packings of nonoverlapping monodisperse cubic particles, following up on our preliminary results [H. Malmir, Sci.... 

According to current researches, graphene oxide (GO) membranes show promising desalination properties due to ease of synthesis, low production cost, and high efficiency. There are several experimental works to study ionic sieving properties of GO membranes. However, it is difficult to characterize atomistic mechanism of water permeation and ion rejection by experimental approaches. On the other hand, there exist a few reports in which the atomistic picture of water permeation across GO membranes is investigated by means of molecular dynamics (MD) simulation. In the present work, in addition to water desalination, the atomic scale mechanism of ion rejection is studied using large scale MD...