Coars E-grained Molecular Dynamics Simulations Of The Anisotropic Phase In Organic Molecular Systems Based On Gay-berne Potential Model

Due to the advantages of computational efficiency and simulation scale,coarse-grained molecular dynamics simulations have become a powerful toolfor molecular modeling study of the various organic molecular systems.Especially in the simulation of biological macromolecules system, comparedto atomistic molecular dynamics and quantum mechanics, the advantage ofcomputational speed is particularly obvious. However, most of coarse-grainedmodels have been designed so as to study specific systems with somelimitations. As a result, it is a meaningful research work to popularize andimprove the relatively common coarse-grained potential models. AsGay-Berne potential model considers the anisotropy of both the potential welldepth and molecular shape, it has been successfully applied to simulate thephase behavior of thermotropic liquid crystal molecules which arecharacterized by the anisotropic structures. Nevertheless, in addition to liquid crystal molecules, many other types of organic molecules also have thischaracteristic. Consequently，it is necessary to examine the feasibility ofapplying Gay-Berne potential model to those molecular systems.A small-scale single coarse-grained bead based on Gay-Berne potentialmodel was used to define the shape of n-butanol molecule whose structurewas optimized by density functional theory calculations. In Comparison to theliquid crystal molecules, n-butanol is too short with small elongation orlength/breadth ratio, and hence a new set of Gay-Berne parameters is neededto develop. Potential energies of four special configurations (side to side, headto head, cross and Tee type) obtained by the density functional theorycalculations were fitted with the Gay-Berne potential energy functions toparameterize the GB potential model. Using coarse-grained moleculardynamics simulations based on Gay-Berne potential model, the coolingprocess of liquid n-butanol was simulated. The simulation details, such asdensity, were set to mimic experimental conditions. Using the d iscontinuouschanges of the thermodynamic and structural properties in the cooling process,we found the glass phase similar to the experimental and estimated that theglass transition temperature as120±10K, which is in good agreement with theexperimental value (120±1K). The results showed that this molecular scalecoarse-grained model is feasible to study the phase behavior of small organicmolecules like butanol.An improved Gay-Berne potential model was also be applied to coarse-grain amphiphilic molecules which often larger than liquid crystalmolecules. This improved model considered the duality of these molecules,and made one end of an amphiphilic molecule strongly attractive to thesolvent, the othe end being only weakly attractive. From coarse-grainedmolecular dynamics simulations based on this improved Gay-Berne potentialmodel, we found that the amphiphilic molecules were freely self-assemble intoa range of amphiphilic structures including micelles, bilayers and inversemicelles with different amphiphile concentrations. The effect of theamphiphile shape in low amphiphile concentration on self-assembly was alsomonitored. Ultimately, we discussed the phase behavior ofwater/oil/amphiphile with different oil concentrations.