@article {2399, title = {Orientational order of near D-3h solutes in nematic liquid crystals}, journal = {Journal of Chemical Physics}, volume = {130}, number = {15}, year = {2009}, note = {ISI Document Delivery No.: 437KLTimes Cited: 2Cited Reference Count: 49Danilovic, Zorana Burnell, E. Elliott}, month = {Apr}, pages = {11}, type = {Article}, abstract = {Solutes that are similar in size, have a shape that is close to D-3h symmetry but contain dissimilar substituent groups (methyl versus chloro, contributing different electrostatic interactions to the anisotropic intermolecular potential), are used to delineate the short- and long-range anisotropic intermolecular interactions that lead to solute orientational order in nematic liquid crystals. The short-range interactions should be similar for all solutes and for D-3h symmetry should yield a single independent order parameter, whereas the long-range interactions are expected to differ with solute. Short-range size and shape mechanisms account for solute orientational order measured in magic mixtures (e.g., 55 wt \% ZLI-1132/N-p-ethoxybenzylidene-p({\textquoteright})-n-butylaniline), whereas additional mechanisms are required in other nematic liquid-crystal solvents. The results obtained for long-range interactions cannot be rationalized in detail using simple mean-field models that incorporate solute dipoles, quadrupoles, or polarizabilities. The results suggest that details of the solute electrostatics may need to be incorporated into the description of the anisotropic intermolecular potential.}, keywords = {AB-INITIO, ELECTRIC-FIELD GRADIENT, electrostatic, interactions, liquid crystals, LIQUID MIXTURES, liquid structure, MEAN TORQUE, molecular orientation, MOLECULAR-HYDROGEN, MONTE-CARLO SIMULATIONS, nematic, NMR, polarisability, POTENTIALS, SHAPE, SOLVENTS}, isbn = {0021-9606}, url = {://000265486300032}, author = {Danilovic, Z. and Burnell, E. E.} } @article {2615, title = {Orientational order of near D-3h solutes in nematic liquid crystals. II. Description via Gay-Berne model with embedded quadrupoles}, journal = {Journal of Chemical Physics}, volume = {130}, number = {15}, year = {2009}, note = {ISI Document Delivery No.: 437KLTimes Cited: 3Cited Reference Count: 19Sokolovskii, R. O. Burnell, E. Elliott}, month = {Apr}, pages = {6}, type = {Article}, abstract = {We perform Monte Carlo simulations of a mixture of soft ellipsoids with embedded quadrupoles as a model of various chloro- and methyl-substituted benzenes dissolved in nematic liquid crystals. We find that oblate Gay-Berne ellipsoids with multiple embedded quadrupoles qualitatively reproduce the trend in the order parameter asymmetry experimentally observed in NMR spectra. The trend is opposite to what is expected on the basis of the interaction of the solute{\textquoteright}s quadrupole with the solvent{\textquoteright}s average electric field gradient "felt" by dissolved dihydrogen molecules. We identify the specific minimum of the solute-solvent interaction energy landscape that may produce the unexpected sign of the order parameter asymmetry that is seen in the experiment and the simulation.}, keywords = {COMPOUNDS, deuterium, dissolving, ELECTRIC-DIPOLE INTERACTIONS, LIQUID MIXTURES, liquid theory, METHODS, Monte Carlo, MONTE-CARLO SIMULATIONS, nematic liquid crystals, nuclear magnetic resonance, ORGANIC, POTENTIALS, SHAPE, SOLVENTS}, isbn = {0021-9606}, url = {://000265486300033}, author = {Sokolovskii, R. O. and Burnell, E. E.} } @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 {2026, title = {Mechanisms of solute orientational order in nematic liquid crystals}, journal = {Journal of Chemical Physics}, volume = {128}, number = {16}, year = {2008}, note = {ISI Document Delivery No.: 295DXTimes Cited: 7Cited Reference Count: 51Burnell, E. Elliott ter Beek, Leon C. Sun, Zhengmin}, month = {Apr}, pages = {10}, type = {Article}, abstract = {The order parameters of a number of different solutes dissolved in a number of different nematic liquid-crystal solvents are measured and compared. It is shown that the order parameters can all be rationalized with the ansatz that there exist two independent ordering mechanisms operating in the liquid crystals employed. With this ansatz it is possible to fit the experimental order parameters to better than 5\%. This opens the possibility of the accurate prediction of order parameters in ordered liquids. (c) 2008 American Institute of Physics.}, keywords = {ELECTRIC-DIPOLE INTERACTIONS, electrostatic, FIELD GRADIENT, interactions, KRISTALLINFLUSSIGEN PHASE, MEAN TORQUE, MOLECULAR-STRUCTURE, MOLEKULAR-STATISTISCHE THEORIE, MONTE-CARLO SIMULATIONS, NMR, SOLVENTS}, isbn = {0021-9606}, url = {://000255456300083}, author = {Burnell, E. E. and ter Beek, L. C. and Sun, Z. M.} } @article {4944, title = {Dipole-induced ordering in nematic liquid crystals. II. The elusive holy grail}, journal = {Journal of Chemical Physics}, volume = {113}, number = {8}, year = {2000}, note = {ISI Document Delivery No.: 345AGTimes Cited: 23Cited Reference Count: 47}, month = {Aug}, pages = {3452-3465}, type = {Article}, abstract = {Similar size and shape molecules with different electric multipoles are used to investigate effects of molecular dipole, quadrupole, and polarizability interactions on the average orientational order of solutes in nematic liquid crystals. Solutes are codissolved in the same sample tube so that the orientational ordering among solutes can be directly compared and analyzed using mean-field models. Permanent dipoles have a negligible influence on solute orientational order. Effects from molecular polarizability interactions could not be separated from short-range interactions. However, order parameters predicted from strong, short-range repulsive forces coupled with interactions between the solute quadrupole and the average electric field gradient felt by the solute are consistent with experimental values. For the nematic mixture 55 wt\% ZLI 1132 in EBBA [N-(pethoxybenzylidene)-p{\textquoteright}-n-butylaniline] the contribution to solute ordering from long-range electrostatic interactions is negligible. (C) 2000 American Institute of Physics. [S0021-9606(00)52232-6].}, keywords = {AB-INITIO, ELECTRIC-DIPOLE, HARD ELLIPSOIDS, MEAN TORQUE, MOLECULAR QUADRUPOLE-MOMENTS, MONTE-CARLO SIMULATIONS, NMR-SPECTRA, ORDER, ORIENTATIONAL, SOLUTES, SOLVENTS}, isbn = {0021-9606}, url = {://000088792800063}, author = {Syvitski, R. T. and Burnell, E. E.} } @article {4896, title = {Forces between like-charged walls in electrolyte solution: Molecular solvent effects at the McMillan-Mayer level}, journal = {Journal of Chemical Physics}, volume = {112}, number = {20}, year = {2000}, note = {ISI Document Delivery No.: 310WCTimes Cited: 13Cited Reference Count: 36}, month = {May}, pages = {8939-8949}, type = {Article}, abstract = {The force between two like-charged walls immersed in electrolyte solution is obtained for models that include solvent effects at the McMillan-Mayer (MM) level. In these models the solvent is not represented by discrete particles but exerts its influence through solvent-averaged ion-ion potentials of mean force which serve as effective potentials. This simplification allows the numerical solution of accurate anisotropic integral equation theories, and the anisotropic hypernetted-chain (AHNC) approximation is used in the present calculations. It is shown that the MM results may differ significantly from those of the primitive model (PM) which treats the solvent as a dielectric continuum. Most interestingly, we find that at the MM level the force between like-charged walls at small separations and with realistic surface charges can be attractive for monovalent counterions. This attraction is due to solvent effects on the effective counterion-counterion interaction and not to the correlated charge fluctuations that give rise to the attractions found for divalent counterions in the PM case. The possible relevance of our observations in the interpretation of experimental force measurements is briefly discussed. (C) 2000 American Institute of Physics. [S0021-9606(00)51720-6].}, keywords = {AQUEOUS-ELECTROLYTES, DOUBLE-LAYERS, electric, HARD-SPHERES, IMAGE, INFINITE DILUTION, INHOMOGENEOUS COULOMB FLUIDS, interactions, ION-ION CORRELATIONS, MICA SURFACES, MONTE-CARLO SIMULATIONS, PLANAR SURFACES}, isbn = {0021-9606}, url = {://000086851200025}, author = {Otto, F. and Patey, G. N.} } @article {4677, title = {Intermolecular potentials in liquid crystals: Comparison between simulations and NMR experiments}, journal = {International Journal of Modern Physics C}, volume = {10}, number = {2-3}, year = {1999}, note = {ISI Document Delivery No.: 222HPTimes Cited: 12Cited Reference Count: 21Meeting on Recent Developments in the Computer Simulations of Liquid CrystalsJUN 18, 1998ERICE, ITALY}, month = {May}, pages = {403-413}, type = {Proceedings Paper}, abstract = {The anisotropic intermolecular forces responsible for the orientational ordering in liquid crystals are probed by comparing Monte Carlo (MC) simulations with experimental nuclear magnetic resonance (NMR) results for solutes in nematic liquid crystals. In a special liquid crystal mixture where all long-range interactions are assumed to be minimized, the models for short-range interactions which best fit NMR experimental solute order parameters also best fit solute order parameters from MC simulations of hard ellipsoids. This is taken as an indication that in this special mixture the intermolecular potential is dominated by short-range forces. However, for liquid crystals where long-range interactions are important, simulations of hard ellipsoids with point quadrupoles cannot reproduce even the gross effects observed with experimental NMR data.}, keywords = {anisotropic intermolecular force, ELECTRIC-DIPOLE INTERACTIONS, interaction, liquid crystal, MOLECULES, Monte Carlo, MONTE-CARLO SIMULATIONS, NEMATIC SOLVENTS, nuclear magnetic resonance experiment, ORDER, ORIENTATIONAL, quadrupole interaction, SHAPE, SHORT-RANGE, SIMULATION, SIZE, SOLUTES}, isbn = {0129-1831}, url = {://000081779000007}, author = {Syvitski, R. T. and Polson, J. M. and Burnell, E. E.} } @article {4218, title = {Prediction from molecular shape of solute orientational order in liquid crystals}, journal = {Chemical Reviews}, volume = {98}, number = {6}, year = {1998}, note = {ISI Document Delivery No.: 127TNTimes Cited: 82Cited Reference Count: 154}, month = {Sep-Oct}, pages = {2359-2387}, type = {Review}, keywords = {ATOM-ATOM POTENTIALS, COUPLINGS, ELECTRIC-FIELD GRADIENT, FLUIDS, HARD-PARTICLE, ISOMERIC STATE APPROXIMATION, MONTE-CARLO SIMULATIONS, MULTIPLE-QUANTUM H-1-NMR, NEMATIC SOLVENTS, NUCLEAR MAGNETIC-RESONANCE, PARTIALLY ORIENTED MOLECULES, SPIN DIPOLAR}, isbn = {0009-2665}, url = {://000076366800007}, author = {Burnell, E. E. and de Lange, C. A.} } @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 {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.} }