@article {2397, title = {Simulation of Water Adsorption on Kaolinite under Atmospheric Conditions}, journal = {Journal of Physical Chemistry A}, volume = {113}, number = {27}, year = {2009}, note = {ISI Document Delivery No.: 466WNTimes Cited: 5Cited Reference Count: 61Croteau, T. Bertram, A. K. Patey, G. N.}, month = {Jul}, pages = {7826-7833}, type = {Article}, abstract = {Grand canonical Monte Carlo calculations are employed to investigate water adsorption on kaolinite at 298 and 235 K. Both basal planes (the Al and Si surfaces) as well as two edge-like surfaces are considered. The general force field CLAYFF is used together with the SPCIE and TIP5P-E models for water. Problems that occur in single slab simulations due to arbitrary truncation of the point charge lattice are identified, and a working remedy is discussed. The edges and the Al surface adsorb water at subsaturation in the atmospherically relevant pressure range. The Si surface remains dry up to saturation. Both edges have a very strong affinity for water and adsorb continuously up to monolayer coverage. The Al surface has a weaker affinity for water but forms a subsaturation monolayer. On the Al surface, the monolayer is formed in an essentially sharp transition, and strong hysteresis is observed upon desorption. This indicates collective behavior among the water molecules which is not present for the edges. Binding energies of singly adsorbed water molecules at 10 K were determined to understand the differences in water uptake by the four kaolinite surfaces. Binding energies (SPC/E) of -21.6, -46.4, -73.5, and -94.1 kJ/mol, were determined for the Si surface, Al surface, unprotonated edge, and protonated edge, respectively. The water monolayer on the Al surface, particularly at 235 K, exhibits hexagonal patterns. However, the associated lattice parameters are not compatible with ice 1h. Water density and hydrogen bonding in the monolayers at both 298 and 235 K were also determined to better understand the structure of the adsorbed water.}, keywords = {ADSORBED, CLAY-MINERALS, COMPUTER-SIMULATION, DYNAMICS, HYDROGEN-BOND, ICE FORMATION, INITIO MOLECULAR-DYNAMICS, LIQUID WATER, MINERAL DUST, MONTE-CARLO SIMULATIONS, NITRIC-ACID, WATER}, isbn = {1089-5639}, url = {://000267694800018}, author = {Croteau, T. and Bertram, A. K. and Patey, G. N.} } @article {2271, title = {Behavior of interacting species in vacancy affinity capillary electrophoresis described by mass balance equation}, journal = {Electrophoresis}, volume = {29}, number = {16}, year = {2008}, note = {ISI Document Delivery No.: 343MCTimes Cited: 0Cited Reference Count: 42Sun, Ying Fang, Ning Chen, David D. Y.}, month = {Aug}, pages = {3333-3341}, type = {Article}, abstract = {Vacancy ACE (VACE) is one of the ACE methods, and has been used to study binding interactions between different biomolecules. Thermodynamic binding constants can be estimated with nonlinear regression methods. With a highly efficient computer simulation program (SimDCCE), it is possible to demonstrate the detailed behaviors of each species during the interaction process under different conditions. In this work, thirteen scenarios in four different combinations of migration orders of the free protein, free drug, and complex formed are studied. The detailed interaction process between protein and ligand is discussed and illustrated based on the mass balance equation, also called mass transfer equation. By properly setting the parameters in the simulation model, the influence of different factors during the interaction process can be well understood.}, keywords = {affinity capillary electrophoresis, binding constant, COMPUTER-SIMULATION, CONSTANTS, DRUG-PROTEIN-BINDING, equation, EXPERIMENTAL VALIDATION, FRONTAL ANALYSIS, HUMAN-SERUM-ALBUMIN, HUMMEL-DREYER, mass balance, method, PERFORMANCE LIQUID-CHROMATOGRAPHY, vacancy affinity capillary electrophoresis, WALL ADSORPTION, ZONE-ELECTROPHORESIS}, isbn = {0173-0835}, url = {://000258856900008}, author = {Sun, Y. and Fang, N. and Chen, D. D. Y.} } @article {1108, title = {General approach to high-efficiency simulation of affinity capillary electrophoresis}, journal = {Analytical Chemistry}, volume = {77}, number = {3}, year = {2005}, note = {ISI Document Delivery No.: 893ZGTimes Cited: 12Cited Reference Count: 22}, month = {Feb}, pages = {840-847}, type = {Article}, abstract = {The differential equation describing electrophoretic migration can be evaluated with various finite difference schemes (FDSs). However, the accuracy and efficiency can be dramatically different depending on the FDS chosen and the way the algorithm is implemented in a computer simulation program. The monotonic transport scheme is used as the algorithm for the hyperbolic part of the differential equation, and the first-order fully explicit scheme is used for the parabolic part of the equation. The combination of these algorithms minimizes the errors and maintains high efficiency. A circular arrangement of the cells in the computer{\textquoteright}s memory is used in the implementation of the algorithms, and the use of concentration thresholds to enable and disable cells along the capillary makes the new algorithm highly efficient. Either thermodynamic or kinetic constants can be used in this program to simulate binding interactions between two species for equilibrium and nonequilibrium affinity CE. Simulation results with various parameters are presented. The simulated peak with proper parameters for an equilibrium affinity CE experiment has shape and position similar to that of the experimental peak. The simulated electropherograms for a nonequilibrium affinity CE experiment also show characteristics of the experimental electropherograms.}, keywords = {COMPUTER-SIMULATION, ELECTROMIGRATION, EQUILIBRIUM MIXTURES, MATHEMATICAL-MODEL, NUMERICAL-SIMULATION, SEPARATIONS, ZONE-ELECTROPHORESIS}, isbn = {0003-2700}, url = {://000226759000024}, author = {Fang, N. and Chen, D. D. Y.} } @article {445, title = {Molecular dynamics simulations of a ferroelectric nematic liquid under shear flow}, journal = {Journal of Chemical Physics}, volume = {117}, number = {18}, year = {2002}, note = {ISI Document Delivery No.: 610YYTimes Cited: 5Cited Reference Count: 47}, month = {Nov}, pages = {8551-8564}, type = {Article}, abstract = {We perform nonequilibrium molecular dynamics simulations to examine the change in orientational order of a ferroelectric nematic liquid crystal under shear flow, specifically planar Couette flow. The orientational order is found to decrease with increasing shear rate. This drop in orientational order is not due to structural changes but is rather a result of the director dynamics being flow unstable. Employing both nonequilibrium and equilibrium molecular dynamics with the director orientation fixed, we determine the shear and twist viscosities which relate the pressure tensor to the shear or strain rate tensor in a nematic liquid crystal under flow. The Miesowicz viscosities are then obtained from linear combinations of the shear and twist viscosities. The short-range spatial structure of the ferroelectric nematic liquid crystal is similar to that of a ferroelectric tetragonal I lattice. The relative magnitudes of the Miesowicz viscosities can be understood by examining the shear stress response of this lattice to a shear deformation. (C) 2002 American Institute of Physics.}, keywords = {BOUNDARY-CONDITIONS, COMPUTER-SIMULATION, CRYSTALS, FLUIDS, MONTE-CARLO, PHASE-TRANSITIONS, rheology, STATE, VISCOSITY}, isbn = {0021-9606}, url = {://000178990700045}, author = {McWhirter, J. L. and Patey, G. N.} } @article {446, title = {Orientational ordering and disordering of a simple dipolar fluid under shear flow}, journal = {Journal of Chemical Physics}, volume = {117}, number = {19}, year = {2002}, note = {ISI Document Delivery No.: 609YVTimes Cited: 4Cited Reference Count: 68}, month = {Nov}, pages = {9016-9027}, type = {Article}, abstract = {Nonequilibrium molecular dynamics simulations are performed for a simple dipolar fluid under planar Couette flow. Under this shear flow, the fluid{\textquoteright}s spatial structure becomes distorted, and the pair distribution function is anisotropic. At low shear rates, the dipoles respond to this distortion by orientationally ordering along an axis where the fluid structure is most compressed, giving a shear-induced ferroelectric fluid state. At high shear rates above a critical value, the orientational order decreases. We argue that this disordering can be attributed to the onset of large fluctuations in the director{\textquoteright}s orientation about the compression axis at the critical shear rate. We also observe the director can "hop" between "up" and "down" directions along the compression axis. These hops are fast and infrequent events. (C) 2002 American Institute of Physics.}, keywords = {BOUNDARY-CONDITIONS, COMPUTER-SIMULATION, DENSITY-FUNCTIONAL THEORY, HARD-SPHERES, LIQUID-CRYSTAL, LIVING POLYMERS, MODEL, NONEQUILIBRIUM-MOLECULAR-DYNAMICS, PHASE-SEPARATION, POLAR CLUSTERS, SELF-DIFFUSION}, isbn = {0021-9606}, url = {://000178934700045}, author = {McWhirter, J. L. and Patey, G. N.} } @article {5027, title = {Pressure-induced change in orientational order of solutes in liquid crystals}, journal = {Chemical Physics Letters}, volume = {337}, number = {4-6}, year = {2001}, note = {ISI Document Delivery No.: 420BPTimes Cited: 1Cited Reference Count: 20}, month = {Apr}, pages = {248-254}, type = {Article}, abstract = {The H-1 and H-1 NMR spectroscopy of the nematic liquid crystal ZLI 1132 containing small amounts of the solutes 1,3,5- trichlorobenzene. p-dichlorobenzene and acetone was investigated as a function of the pressure of a mixture of molecular hydrogen and deuterium gases above the sample. A general increase of solute orientational order with pressure was observed. Differences in behavior of the orientational order of the hydrogens compared to the other solutes are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.}, keywords = {COMPUTER-SIMULATION, density, MAGNETIC-RESONANCE, MOLECULES, NEMATIC PHASE, NMR, SOLVENTS, TEMPERATURE-DEPENDENCE}, isbn = {0009-2614}, url = {://000167984300004}, author = {Burnell, E. E. and de Lange, C. A. and Gaemers, S.} } @article {4849, title = {Integral equation theory for dipolar hard sphere fluids with fluctuating orientational order}, journal = {Journal of Chemical Physics}, volume = {112}, number = {8}, year = {2000}, note = {ISI Document Delivery No.: 284RDTimes Cited: 21Cited Reference Count: 53}, month = {Feb}, pages = {3832-3844}, type = {Article}, abstract = {We present an integral equation approach to the structural and thermodynamic properties of a fluid of partially aligned dipolar hard spheres. To relate the two-particle correlation functions to the anisotropic singlet density, we mainly employ the Lovett-Mou-Buff-Wertheim equation. We show that, as in the isotropic case, the mean-spherical approximation and the reference hypernetted chain (RHNC) closures lead to quite different results. This is particularly true at high coupling strengths, where the RHNC theory shows a transition from an isotropic to a ferroelectric fluid phase. The predicted transition temperatures are very close to those one obtains from the RHNC theory for the isotropic fluid. (C) 2000 American Institute of Physics. [S0021-9606(00)50707-7].}, keywords = {BOUNDARY-CONDITIONS, COMPUTER-SIMULATION, DENSITY-FUNCTIONAL THEORY, EXTERNAL MAGNETIC-FIELD, HEISENBERG SPIN FLUID, HYPERNETTED-CHAIN APPROXIMATION, LIQUID-VAPOR INTERFACE, NONSPHERICAL PARTICLES, PARALLEL SPHEROCYLINDERS, PERIODIC, PHASE-TRANSITIONS}, isbn = {0021-9606}, url = {://000085345300041}, author = {Klapp, S. H. L. and Patey, G. N.} } @article {4749, title = {Isotropic fluid phases of dipolar hard spheres}, journal = {Physical Review Letters}, volume = {84}, number = {1}, year = {2000}, note = {ISI Document Delivery No.: 271HJTimes Cited: 86Cited Reference Count: 28}, month = {Jan}, pages = {115-118}, type = {Article}, abstract = {Monte Carlo simulations are used to calculate the equation of state and free energy-of dipolar hard sphere fluids at low temperatures and densities. Evidence for the existence of isotropic-fluid-isotropic-fluid phase transitions is presented and discussed. Condensation in the dipolar hard sphere fluid is unusual in that it is not accompanied by large energy or entropy changes. An explanation of this behavior is put forward.}, keywords = {CLUSTERS, COMPUTER-SIMULATION, CONDENSATION, LIQUID, orientational order, SYSTEMS}, isbn = {0031-9007}, url = {://000084587900029}, author = {Camp, P. J. and Shelley, J. C. and Patey, G. N.} } @article {4479, title = {A Monte Carlo study of model electrorheological fluids}, journal = {Journal of Chemical Physics}, volume = {111}, number = {7}, year = {1999}, note = {ISI Document Delivery No.: 222GBTimes Cited: 4Cited Reference Count: 26}, month = {Aug}, pages = {3278-3287}, type = {Article}, abstract = {Monte Carlo results for both spherical and nonspherical electrorheological (ER) particles are described. The ER particles are modeled as hard spheres or hard ellipsoids of revolution with much smaller charged hard spheres (ions) constrained to their inner surface. NVT Monte Carlo calculations show that these models display the strong polarization and chain formation characteristic of ER fluids. Both prolate and oblate ER particles align with their longest axis directed along the applied field allowing for larger induced dipole moments than those obtained for spherical ER particles of equal volume. In all cases it is found that chaining occurs at relatively high fields where the induced dipole moments are approaching their maximum value. An interesting feature of nonspherical ER particles is the field-induced orientational order. It is found that even slightly nonspherical ER particles are highly ordered by fields which are weaker than those required to induce chain formation. Very weak fields are sufficient to generate strong orientational order in prolate ER particles with moderate aspect ratios. Further, field-ordered oblate ER particles tend to align their symmetry (short) axes to form a biaxial phase at high densities. The field-induced, liquid-crystal-like behavior of nonspherical ER particles is discussed in detail. (C) 1999 American Institute of Physics. [S0021-9606(99)51131-8].}, keywords = {COMPUTER-SIMULATION, FIELD, FORCES, POINT-DIPOLE LIMIT, SHEAR RATE RESPONSE, SUSPENSIONS}, isbn = {0021-9606}, url = {://000081774700051}, author = {Blair, M. J. and Patey, G. N.} } @article {4198, title = {Gas-liquid coexistence and demixing in systems with highly directional pair potentials}, journal = {Physical Review E}, volume = {57}, number = {5}, year = {1998}, note = {ISI Document Delivery No.: ZP583Times Cited: 19Cited Reference Count: 21Part B}, month = {May}, pages = {5682-5686}, type = {Article}, abstract = {Recent computer simulation studies strongly indicate that fluids of dipolar hard spheres do not display gas-isotropic liquid coexistence. In this paper we discuss a second example that also exhibits this rather unexpected behavior. This is a simple liquid-crystal model that we explore employing Gibbs ensemble Monte Carlo (GEMC) methods. It is shown that the system has clear gas-nematic liquid coexistence, but that the gas-isotropic liquid coexistence line is completely missing from the phase diagram. We attribute this to the highly directional nature of the attractive potential and argue that similar considerations are likely of relevance in the dipolar hard-sphere case as well. We also use GEMC techniques to investigate demixing in binary mixtures of neutral and dipolar hard spheres. For similar mixtures of neutral and charged have spheres, it is known that demixing is essentially condensation of the Coulombic fluid weakly influenced by the background of neutral hard spheres. Therefore, given that dipolar hard spheres do not condense, whether or not the present mixtures demix is an interesting question. In fact, demi?ring is observed and, moreover, the transition temperatures are in reasonable agreement with those predicted by the same integral equation theories that incorrectly predict condensation of the pure dipolar fluid. The critical temperature decreases rapidly with decreasing diameter of the neutral species consistent with the lack of gas-isotropic liquid coexistence for pure dipolar hard spheres. Clearly, for the present model demixing and dipolar condensation are not closely related phenomena as they are in the Coulombic systems. The neutral species appears to reduce the formation of dipolar "chains" or "clusters" that inhibit condensation of the purl dipolar hard-sphere fluid.}, keywords = {COMPUTER-SIMULATION, CRYSTAL MODELS, DIPOLAR HARD-SPHERES, FLUID, GIBBS ENSEMBLE, INSTABILITY, MIXTURE, MONTE-CARLO, orientational order, PHASE}, isbn = {1063-651X}, url = {://000073768000025}, author = {Blair, M. J. and Patey, G. N.} } @article {3886, title = {Ferroelectric and dipolar glass phases of noncrystalline systems}, journal = {Physical Review E}, volume = {56}, number = {1}, year = {1997}, note = {ISI Document Delivery No.: XM377Times Cited: 28Cited Reference Count: 43Part B}, month = {Jul}, pages = {562-570}, type = {Article}, abstract = {In a recent Letter [Phys. Rev. Lett. 75, 2360 (1995)] we briefly discussed the existence and nature of ferroelectric order in positionally disordered dipolar materials. Here we report further results and give a complete description of our work. Simulations of randomly frozen and dynamically disordered dipolar soft spheres are used to study ferroelectric ordering in noncrystalline systems. We also give a physical interpretation of the simulation results in terms of short- and long-range interactions. Cases where the dipole moment has one, two, and three components (Ising, XY, and XYZ models, respectively) are considered. It is found that the Ising model displays ferroelectric phases in frozen amorphous systems, while the XY and XYZ models form dipolar glass phases at low temperatures. In the dynamically disordered model the equations of motion are decoupled such that particle translation is completely independent of the dipolar forces. These systems spontaneously develop long-range ferroelectric order at nonzero temperature: despite the absence of any fined-tuned short-range spatial correlations favoring dipolar order. Furthermore, since this is a nonequilibrium model, we find that the paraelectric to ferroelectric transition depends on the particle mass. For the XY and XYZ models, the critical temperatures extrapolate to zero as the mass of the particle becomes infinite, whereas for the Ising model the critical temperature is almost independent of mass, and coincides with the ferroelectric transition found for the randomly frozen system at the same density. Thus in the infinite mass limit the results of the frozen amorphous systems are recovered.}, keywords = {COMPUTER-SIMULATION, ELECTROSTATIC SYSTEMS, interactions, LIQUID-CRYSTAL, LONG-RANGE, ORIENTATIONAL GLASSES, PERIODIC BOUNDARY-CONDITIONS, RANDOM ANISOTROPY, RANDOM LEVY FLIGHTS, SPONTANEOUS MAGNETIC ORDER, VECTOR SPIN-GLASSES}, isbn = {1063-651X}, url = {://A1997XM37700005}, author = {Ayton, G. and Gingras, M. J. P. and Patey, G. N.} } @article {3924, title = {An investigation of the influence of solute size and insertion conditions on solvation thermodynamics}, journal = {Journal of Chemical Physics}, volume = {106}, number = {19}, year = {1997}, note = {ISI Document Delivery No.: WZ032Times Cited: 32Cited Reference Count: 52}, month = {May}, pages = {8165-8195}, type = {Article}, abstract = {In this paper we examine the influence of solute size and insertion conditions on solvent structural changes and excess thermodynamic properties in the infinite dilution limit. A general integral equation approach which can be applied under arbitrary conditions is given and isothermal-isochoric and isothermal-isobaric insertions are discussed in detail. Scaling relationships valid in the large solute limit are determined for both structural and thermodynamic properties. This is done by considering macroscopic thermodynamic relationships and explicit evaluation of low solvent density expansions of pair correlation functions. The hypernetted-chain and reference hypernetted-chain closure approximations are used to obtain numerical results for the insertion of hard sphere solutes of varying diameter into hard sphere, dipolar hard sphere and water-like solvents. The results obtained give a good deal of insight into the nature of solvation of inert solutes. It is shown that for all three solvents the excess properties are very well represented by a function obtained by summing terms proportional to the solute volume, surface area and diameter. One would expect such a result for large solutes, but here we show that this expression extrapolates all the way down to solutes comparable in size to the solvent particles. Further, it is shown that both the numerical value, and, more importantly, the physical interpretation of the excess thermodynamic properties strongly depend on the insertion conditions. Under all insertion conditions the chemical potential is a local property in the sense that it is completely determined by solute-solvent correlations which are important only in the immediate vicinity of the solute. However, this is not true of the excess energy, enthalpy and entropy which all contain nonlocal contributions arising essentially from changes in the actual or effective solvent density depending on the insertion conditions. We demonstrate that the nonlocal contributions can be very significant and therefore the excess energies, enthalpies and entropies often cannot provide useful information about solvent structure near solutes. This has significant implications for models which attempt to rationalize excess thermodynamics in terms of local solvent structure in the vicinity of solute particles. (C) 1997 American Institute of Physics.}, keywords = {COMPUTER-SIMULATION, ELECTROLYTE-SOLUTIONS, FREE-ENERGIES, HARD-SPHERES, HYDROPHOBIC HYDRATION, HYPERNETTED-CHAIN APPROXIMATION, INVARIANT EXPANSION, MEAN, ORNSTEIN-ZERNIKE EQUATION, SPHERICAL MODEL, TEMPERATURE-DEPENDENCE}, isbn = {0021-9606}, url = {://A1997WZ03200027}, author = {Cann, N. M. and Patey, G. N.} } @article {3887, title = {Liquid crystal phases of dipolar discotic particles}, journal = {Physical Review E}, volume = {55}, number = {1}, year = {1997}, note = {ISI Document Delivery No.: WD545Times Cited: 15Cited Reference Count: 21Part A}, month = {Jan}, pages = {447-454}, type = {Article}, abstract = {Fluids of dipolar oblate ellipsoids of revolution are investigated in detail employing molecular dynamics simulations. For aspect ratios (height-to-breadth) between similar to 1.2 and similar to 3, it is shown that these systems may form two liquid crystal phases. These are a ferroelectric phase which is stable at higher temperatures and an antiferroelectric columnar phase which is stable at lower temperatures. A partial phase diagram is given and the important structural features of these phases are determined and discussed.}, keywords = {COMPUTER-SIMULATION, ELLIPSOIDS, MODEL, MOLECULES, MONTE-CARLO SIMULATIONS, NEMATIC PHASE, orientational order, SPHERES, SYSTEMS}, isbn = {1063-651X}, url = {://A1997WD54500056}, author = {Ayton, G. and Wei, D. Q. and Patey, G. N.} } @article {4128, title = {Modeling and structure of mercury-water interfaces}, journal = {Journal of Chemical Physics}, volume = {107}, number = {6}, year = {1997}, note = {ISI Document Delivery No.: XP280Times Cited: 37Cited Reference Count: 78}, month = {Aug}, pages = {2122-2141}, type = {Article}, abstract = {The modeling and nature of the physisorption of water at the metal (Hg)-water interface is explored in this paper. We have evaluated potential models that fit into three general classes that are employed in the literature. These classes are distinguished by the manner in which the isotropic interactions between the metal and the water are modeled: namely, as non-attractive, weakly attractive, and strongly attractive. In the present studies the metal is described by a jellium model. In our model, in addition to the isotropic water potential there is an interaction between the jellium and the water molecules which depends on the orientation of the water molecule with respect to the metal surface. We find that hard potentials without isotropic attractive terms dewet. The density of water near hydrocarbon-like potentials remains close to the bulk value but the interaction isn{\textquoteright}t strong enough to structure the water near the interface, nor are the adsorption energies sufficiently high. The strongly attractive potentials seem to be the most appropriate. For such models we have checked the sensitivity of the results to the parameters in our model including surface corrugation. We find that the structural results are insensitive to the parameters employed suggesting that they not only provide a good classical description of the Hg-water interface but may be readily adaptable to describe the physisorption of water on metals in general. Although we find the layering of water molecules and the pattern of hydrogen bonding near these surfaces, which have been described as ice-like in previous studies, the actual arrangement of the water molecules near these surfaces is distinctly different from the structure of ice. (C) 1997 American Institute of Physics.}, keywords = {CHARGED ELECTRODES, COMPUTER-SIMULATION, DOUBLE-LAYER, ELECTROLYTE, HALIDE-IONS, INTERFACE, LIQUID WATER, METAL INTERFACE, MOLECULAR-DYNAMICS SIMULATION, SURFACE, TIP4P WATER}, isbn = {0021-9606}, url = {://A1997XP28000045}, author = {Shelley, J. C. and Patey, G. N. and Berard, D. R. and Torrie, G. M.} } @article {4107, title = {Monte Carlo simulations of solute ordering in nematic liquid crystals: Shape anisotropy and quadrupole-quadrupole interactions as orienting mechanisms}, journal = {Physical Review E}, volume = {55}, number = {4}, year = {1997}, note = {ISI Document Delivery No.: WV249Times Cited: 17Cited Reference Count: 51}, month = {Apr}, pages = {4321-4337}, type = {Article}, abstract = {Monte Carlo computer simulations were used to investigate the effects of shape anisotropy and electrostatic interactions as mechanisms for orientational ordering of solutes in nematic liquid crystals. The simulation results were analyzed in terms of two theories of solute ordering which derive mean-field orientational potentials from the intermolecular pair potential. In the calculations, solute and solvent molecular shapes were approximated by hard ellipsoids. Most simulations also incorporated the interaction between point quadrupole moments placed at the centers of the ellipsoids. In the hard-core systems, orientational order parameters and distribution functions were calculated for a collection of different solutes under a variety of conditions. A theory due to Terzis and Photinos [Mol. Phys. 83, 847 (1994)] was found to underestimate the effect of shape anisotropy on orientational ordering drastically. The introduction of an effective solvent packing fraction was unable to improve the predictive power of the theory significantly. The quadrupolar systems were used to investigate a mean-field model for solute ordering which considers an interaction between the solute molecular quadrupole moment with an average electric-field gradient. The simulations indicate that the electric-field gradient sampled by the solute is highly dependent on the properties of the solute, contrary to some experimental evidence. Further, the effects of the intermolecular quadrupolar interactions on orientational ordering and the electric-field gradient were analyzed using a mean-field potential derived here and based on the theory due to Emsley, Palke, and Shilstone [Liq. Cryst. 9, 649 (1991)]. This model was found to provide a qualitatively correct but quantitatively imprecise prediction of orientational ordering.}, keywords = {acetylene, COMPUTER-SIMULATION, ELECTRIC-DIPOLE INTERACTIONS, HARD ELLIPSOIDS, MEAN TORQUE, MOLECULAR-HYDROGEN, NMR, orientational order, POTENTIALS, SOLVENTS}, isbn = {1063-651X}, url = {://A1997WV24900067}, author = {Polson, J. M. and Burnell, E. E.} } @article {4106, title = {Nematic-isotropic phase coexistence in a Lebwohl-Lasher model binary liquid crystal mixture}, journal = {Chemical Physics Letters}, volume = {281}, number = {1-3}, year = {1997}, note = {ISI Document Delivery No.: YP239Times Cited: 12Cited Reference Count: 31}, month = {Dec}, pages = {207-211}, type = {Article}, abstract = {Monte Carlo computer simulations were used to investigate the phase behaviour of a Lebwohl-Lasher binary liquid-crystal mixture. A finite-size scaling analysis confirmed the first-order nature of the transition. The calculated nematic-isotopic phase coexistence region and the orientational order parameters for the two species along the phase boundary for a sample system were found to deviate significantly from those predicted by a mean-field theory. Increasing the difference between the isotropic components of the pair-potential of the two species resulted in a broadening of the coexistence region. (C) 1997 Elsevier Science B.V.}, keywords = {1ST-ORDER MELTING TRANSITION, ANISOTROPIC SYSTEMS, BEHAVIOR, COMPUTER-SIMULATION, fluctuations, LATTICE, LIPID BILAYERS, MONTE-CARLO, POTTS-MODEL}, isbn = {0009-2614}, url = {://000071256600031}, author = {Polson, J. M. and Burnell, E. E.} } @article {3898, title = {Structure of the metal aqueous electrolyte solution interface}, journal = {Journal of Chemical Physics}, volume = {107}, number = {12}, year = {1997}, note = {ISI Document Delivery No.: XX493Times Cited: 24Cited Reference Count: 47}, month = {Sep}, pages = {4719-4728}, type = {Article}, abstract = {Theoretical results are given for aqueous electrolyte solutions in contact with uncharged metallic surfaces. The metal is modeled as a jellium slab and is treated using local density functional theory. The solution structure is obtained using the reference hypernetted-chain theory. The two phases interact electrostatically and the coupled theories are iterated to obtain fully self-consistent results for the electron density of the metal and surface-particle correlation functions. The metal-induced structure of pure water and aqueous electrolyte solutions as well as the electrostatic potential drop across the interface are discussed in detail. The results are compared with those for ions in simple dipolar solvents. It is found that the water molecules are ordered by the metal field and that the surface-induced solvent structure strongly influences the ion distributions. (C) 1997 American Institute of Physics.}, keywords = {CHARGED ELECTRODES, COMPUTER-SIMULATION, ELECTRICAL DOUBLE-LAYER, HALIDE-IONS, INTEGRAL-EQUATION THEORIES, LIQUID WATER, MERCURY-WATER INTERFACE, MOLECULAR-DYNAMICS SIMULATION, PLANAR WALL, SOLVENT MODEL}, isbn = {0021-9606}, url = {://A1997XX49300029}, author = {Berard, D. R. and Kinoshita, M. and Cann, N. M. and Patey, G. N.} } @article {3809, title = {Boundary condition effects in simulations of water confined between planar walls}, journal = {Molecular Physics}, volume = {88}, number = {2}, year = {1996}, note = {ISI Document Delivery No.: UN985Times Cited: 86Cited Reference Count: 32}, month = {Jun}, pages = {385-398}, type = {Article}, abstract = {In computer simulations of water between hydrophobic walls the results exhibit a strong dependence upon the boundary conditions applied. With the minimum image (MI) convention the water molecules tend to be orientationally ordered throughout the simulation cell (Valleau, J. P., and Gardner, A. A., 1987, J. chem. Phys., 86, 4162) whereas, if a spherical cut-off (SC) is applied, strong orientational order is found only in the immediate vicinity of the surface (Lee, C. Y., McCammon, J. A., and Rossky, P. J., 1984, J. chem. Phys., 80, 4448). These conflicting observations have remained unresolved, and clearly raise troubling questions concerning the validity of simulation results for water between surfaces of all types. In the present paper we explore this problem by carrying out a detailed analysis of the results obtained with various types of boundary condition. These include Ewald calculations carried out with a central simulation cell adapted to describe the slab geometry of interest. It is shown that the order observed in MI calculations is an artefact of that particular truncation. The reason for this is isolated and discussed. Similar problems are found if a cylindrical cut-off is employed. The Ewald and SC methods gave qualitatively similar results for systems similar to those considered in previous simulations. However, for some geometries problems can also arise with the SC method. We conclude that in general the slab-adapted Ewald method is the safest choice.}, keywords = {ADSORPTION, CHARGED ELECTRODES, COMPUTER-SIMULATION, IONS, LIQUID WATER, METAL WALLS, models, MOLECULAR-DYNAMICS SIMULATION, MONTE-CARLO SIMULATIONS, SURFACE}, isbn = {0026-8976}, url = {://A1996UN98500006}, author = {Shelley, J. C. and Patey, G. N.} } @article {3596, title = {Ferroelectric order in model discotic nematic liquid crystals}, journal = {Physical Review Letters}, volume = {76}, number = {2}, year = {1996}, note = {ISI Document Delivery No.: TN761Times Cited: 31Cited Reference Count: 12}, month = {Jan}, pages = {239-242}, type = {Article}, abstract = {Monte Carlo calculations are used to examine orientational order in fluids of disk-shape particles with embedded dipoles. The dipoles are distributed over a circular {\textquoteright}{\textquoteright}patch{\textquoteright}{\textquoteright} of finite size. It is shown that such systems may undergo spontaneous polarization to form a stable ferroelectric discotic nematic phase.}, keywords = {COMPUTER-SIMULATION, ELECTROSTATIC SYSTEMS, MONTE-CARLO, orientational order, PERIODIC BOUNDARY-CONDITIONS, PHASE}, isbn = {0031-9007}, url = {://A1996TN76100021}, author = {Ayton, G. and Patey, G. N.} } @article {3801, title = {Monte Carlo simulations of orientational ordering of solutes in a nematic solvent: Comparison with mean-field models}, journal = {Molecular Physics}, volume = {88}, number = {3}, year = {1996}, note = {ISI Document Delivery No.: UT951Times Cited: 16Cited Reference Count: 23}, month = {Jun}, pages = {767-782}, type = {Article}, abstract = {Monte Carlo simulations were used to study orientational ordering of solutes in a nematic phase. Nematogens were modelled as hard prolate ellipsoids with an axis ratio of 5:1. Solutes were also modelled as hard prolate ellipsoids, with a variety of sizes and shape anisotropies. Solute order parameters and singlet orientational distribution functions were analysed using several mean-field models. The results confirm that these empirical mean-field potentials are closely linked to the anisotropic short-range repulsive forces that are crucial for the formation of the nematic phase.}, keywords = {ANISOTROPIC SYSTEMS, COMPUTER-SIMULATION, ELECTRIC-DIPOLE INTERACTIONS, LIQUID-CRYSTALS, MOLECULES, NEMATOGEN, PHASE, POTENTIALS, SIZE}, isbn = {0026-8976}, url = {://A1996UT95100015}, author = {Polson, J. M. and Burnell, E. E.} } @article {3233, title = {A GENERALIZED GAUSSIAN OVERLAP MODEL FOR FLUIDS OF ANISOTROPIC PARTICLES}, journal = {Journal of Chemical Physics}, volume = {102}, number = {22}, year = {1995}, note = {ISI Document Delivery No.: RC468Times Cited: 18Cited Reference Count: 18}, month = {Jun}, pages = {9040-9047}, type = {Article}, keywords = {COMPUTER-SIMULATION, GAY-BERNE MODEL, LIQUID-CRYSTAL, PHASE-DIAGRAM, SYSTEM}, isbn = {0021-9606}, url = {://A1995RC46800036}, author = {Ayton, G. and Patey, G. N.} } @article {3232, title = {ORIENTATIONAL ORDERING IN SPATIALLY DISORDERED DIPOLAR SYSTEMS}, journal = {Physical Review Letters}, volume = {75}, number = {12}, year = {1995}, note = {ISI Document Delivery No.: RU811Times Cited: 40Cited Reference Count: 27}, month = {Sep}, pages = {2360-2363}, type = {Article}, abstract = {This Letter addresses basic questions concerning ferroelectric order in positionally disordered dipolar materials. Three models distinguished by dipole vectors that have one, two, or three components are studied by computer simulation. Randomly frozen and dynamically disordered media are considered. It is shown that ferroelectric order is possible in spatially random systems, but that its existence is very sensitive to the dipole vector dimensionality and the motion of the medium. A physical analysis of our results provides significant insight into the nature of ferroelectric transitions.}, keywords = {COMPUTER-SIMULATION, ELECTROSTATIC SYSTEMS, FLIGHTS, LONG-RANGE INTERACTIONS, models, PERIODIC BOUNDARY-CONDITIONS, RANDOM ANISOTROPY, RANDOM LEVY, SPIN-GLASSES}, isbn = {0031-9007}, url = {://A1995RU81100027}, author = {Ayton, G. and Gingras, M. J. P. and Patey, G. N.} } @article {2981, title = {DIELECTRIC-RELAXATION OF ELECTROLYTE-SOLUTIONS - MOLECULAR-DYNAMICS AND THEORETICAL RESULTS FOR IONS IN SIMPLE DIPOLAR SOLVENTS}, journal = {Journal of Chemical Physics}, volume = {100}, number = {11}, year = {1994}, note = {ISI Document Delivery No.: NN731Times Cited: 25Cited Reference Count: 21}, month = {Jun}, pages = {8385-8391}, type = {Article}, abstract = {Computer simulation and theoretical results are given for the frequency dependent dielectric function of model electrolyte solutions. The influences of salt concentration, ionic charge, and solvent dipole moment are discussed. It is found that a substantial salt induced dielectric decrement; persists up to the dispersion frequency. At higher frequencies, however, the dielectric constant-of the solution is larger;than that of the solvent giving a salt induced dielectric increment.}, keywords = {COMPUTER-SIMULATION, CONDUCTIVITY, CONSTANT, ELECTRICAL-PROPERTIES, electrostatic, LIQUIDS, PERIODIC BOUNDARY-CONDITIONS, SYSTEMS}, isbn = {0021-9606}, url = {://A1994NN73100060}, author = {Chandra, A. and Patey, G. N.} } @article {2748, title = {DIELECTRIC-RELAXATION OF DIPOLAR LIQUIDS}, journal = {Journal of Chemical Physics}, volume = {99}, number = {3}, year = {1993}, note = {ISI Document Delivery No.: LN782Times Cited: 19Cited Reference Count: 33}, month = {Aug}, pages = {2068-2073}, type = {Article}, abstract = {An approximate expression is derived for the dielectric function epsilon(k, omega). The theory includes inertial and non-Markovian effects and is free of adjustable parameters. For the k = 0 case, detailed comparisons are made with computer simulation results for dipolar soft-sphere and Stockmayer fluids, and the theory is shown to be qualitatively sound at both low and high frequencies. The present approximation should be very useful in developing a theory of solvation dynamics which properly includes important inertial effects.}, keywords = {COMPUTER-SIMULATION, electrostatic, equation, INVARIANT EXPANSION, ION SOLVATION, LIQUIDS, MEAN SPHERICAL MODEL, MOLECULAR LIQUIDS, ORNSTEIN-ZERNIKE, PERIODIC BOUNDARY-CONDITIONS, POLAR, SOLVATION DYNAMICS, SYSTEMS}, isbn = {0021-9606}, url = {://A1993LN78200067}, author = {Chandra, A. and Wei, D. Q. and Patey, G. N.} } @article {2750, title = {DIELECTRIC-RELAXATION OF ELECTROLYTE-SOLUTIONS - IS THERE REALLY A KINETIC DIELECTRIC DECREMENT}, journal = {Journal of Chemical Physics}, volume = {98}, number = {6}, year = {1993}, note = {ISI Document Delivery No.: KU222Times Cited: 31Cited Reference Count: 34}, month = {Mar}, pages = {4959-4966}, type = {Article}, abstract = {The dielectric behavior of model electrolyte solutions is studied by molecular dynamics simulations. For the systems considered, it is found that the zero-frequency dielectric constant depends only on equilibrium properties and that there is no measurable {\textquoteright}{\textquoteright}kinetic dielectric decrement.{\textquoteright}{\textquoteright} A theoretical explanation of the simulation results is presented. It is argued that no kinetic dielectric decrement exists for spherical ions in solvents of arbitrary molecular symmetry.}, keywords = {AQUEOUS-ELECTROLYTES, COMPUTER-SIMULATION, CONSTANT, DISPERSION, DYNAMICS, ELECTROSTATIC SYSTEMS, friction, MOLECULAR THEORY, PERIODIC BOUNDARY-CONDITIONS, polarization}, isbn = {0021-9606}, url = {://A1993KU22200067}, author = {Chandra, A. and Wei, D. Q. and Patey, G. N.} } @article {2749, title = {THE FREQUENCY-DEPENDENT CONDUCTIVITY OF ELECTROLYTE-SOLUTIONS}, journal = {Journal of Chemical Physics}, volume = {99}, number = {3}, year = {1993}, note = {ISI Document Delivery No.: LN782Times Cited: 30Cited Reference Count: 25}, month = {Aug}, pages = {2083-2094}, type = {Article}, abstract = {The frequency dependent conductivity, sigma(omega), of model electrolyte solutions is investigated employing molecular dynamics simulations. Approximate analytical theories are also derived and evaluated. It is found that sigma(omega) is generally not a simple function and that its detailed frequency dependence contains much useful information about the structure and dynamics of ionic solutions. By varying molecular and state parameters such as the dipole moment and moment of inertia of the solvent, the ionic charge, the solution density, etc., we are able to obtain a physical interpretation of the behavior of sigma(omega). For example, very interesting dynamical solvation effects as well as features associated with ion pairs are identified and described.}, keywords = {COMPUTER-SIMULATION, CONSTANT, DYNAMICS, ELECTROSTATIC SYSTEMS, FLUID, ION, MOLECULAR THEORY, PERIODIC BOUNDARY-CONDITIONS}, isbn = {0021-9606}, url = {://A1993LN78200070}, author = {Chandra, A. and Wei, D. Q. and Patey, G. N.} } @article {2747, title = {MICROSCOPIC THEORY OF SOLVATION DYNAMICS IN DIPOLAR LIQUIDS}, journal = {Journal of Chemical Physics}, volume = {99}, number = {7}, year = {1993}, note = {ISI Document Delivery No.: LY603Times Cited: 48Cited Reference Count: 27}, month = {Oct}, pages = {4926-4931}, type = {Article}, abstract = {A self contained microscopic theory is described for ion solvation dynamics in dipolar fluids. The theory takes account of inertial and non-Markovian effects which are of critical importance for the fast initial phase of the relaxation of the ion-solvent energy. The theory also includes diffusional effects important at long times. The results obtained are shown to be in good agreement with recent computer simulation studies of ions in Stockmayer solvents.}, keywords = {COMPUTER-SIMULATION, DIELECTRIC-CONSTANT, ELECTROSTATIC SYSTEMS, FLUID, ION SOLVATION, MOLECULAR LIQUIDS, PERIODIC BOUNDARY-CONDITIONS, relaxation, SOLVENT}, isbn = {0021-9606}, url = {://A1993LY60300004}, author = {Chandra, A. and Wei, D. Q. and Patey, G. N.} } @article {2930, title = {ORIENTATIONAL ORDER IN SIMPLE DIPOLAR FLUIDS - DENSITY-FUNCTIONAL THEORY AND ABSOLUTE-STABILITY CONDITIONS}, journal = {Physical Review E}, volume = {47}, number = {1}, year = {1993}, note = {ISI Document Delivery No.: KY134Times Cited: 59Cited Reference Count: 29}, month = {Jan}, pages = {506-512}, type = {Article}, abstract = {The formation of ferroelectric liquid crystals by simple dipolar models is investigated using density-functional theory and absolute-stability analysis. It is emphasized that for such systems well defined results can only be found by specifying exactly how the long-range dipolar interactions are treated. Explicit formal expressions are derived for mean-reaction-field boundary conditions and these are combined with integral-equation approximations in order to obtain numerical results for fluids of dipolar hard and soft spheres. The calculations predict isotropic-to-ferroelectric-nematic transitions in qualitative agreement with computer simulations. The quantitative agreement, however, is rather poor.}, keywords = {COMPUTER-SIMULATION, ELECTROSTATIC SYSTEMS, equation, HARD-SPHERES, INVARIANT EXPANSION, MEAN SPHERICAL MODEL, ORNSTEIN-ZERNIKE, PERIODIC BOUNDARY-CONDITIONS, POLAR SYSTEMS, TRANSITION}, isbn = {1063-651X}, url = {://A1993KY13400062}, author = {Wei, D. Q. and Patey, G. N. and Perera, A.} } @article {7376, title = {FERROELECTRIC LIQUID-CRYSTAL AND SOLID-PHASES FORMED BY STRONGLY INTERACTING DIPOLAR SOFT SPHERES}, journal = {Physical Review A}, volume = {46}, number = {12}, year = {1992}, note = {ISI Document Delivery No.: KE871Times Cited: 120Cited Reference Count: 22}, month = {Dec}, pages = {7783-7792}, type = {Article}, abstract = {Molecular-dynamics simulation results are reported for systems of strongly interacting dipolar soft spheres. Calculations have been carried out along two isotherms and the structure of the liquid-crystal and solid phases obtained is described in detail. It is found that in addition to the ferroelectric nematic phase we previously reported [Phys. Rev. Lett. 68, 2043 (1992)], liquid crystals with columnar order can also be obtained. The model freezes to form a ferroelectric solid which is shown to have a tetragonal I crystal structure The influence of different boundary conditions upon the simulation results is also discussed.}, keywords = {COMPUTER-SIMULATION, FLUID, MOLECULAR-DYNAMICS, SYSTEMS}, isbn = {1050-2947}, url = {://A1992KE87100054}, author = {Wei, D. Q. and Patey, G. N.} }