Organic liquids, Monte Carlo simulations

Abstract Monte Carlo simulations of lattice spin models are a powerful method for the investigation of confined nematic liquid crystals and allow for a study of the molecular organization and thermod3mamics of these systems. Investigations of models of polymer-dispersed liquid cr3rstals are reviewed devoting particular attention to the calculation of deuterium NMR spectra from the simulation data. 

We have described lattice spin models for the simulation of polymer-dispersed liquid crystals. The biggest advantage of Monte Carlo simulations is the possibility of investigating the system at a microscopic level, and to calculate thermodynamic properties and their specific order parameters suitable for different types of PDLC. Molecular organizations can be investigated by calculating the order parameters point by point across the droplet. Moreover, it is possible to calculate experimental observables like optical textures and, as discussed here, NMR line shapes. We have given an overview of the method and some applications to models of PDLC with radial and bipolar boundary conditions, and considered the effect of orientational and translational diffusion on the spectra. We have examined in particular under what conditions the NMR spectra of the deuterated nematic can provide reliable information on the actual boundaries present in these submicron size droplets. 

Molecular simulations have been used to obtain thermodynamic properties and phase equilibria data of ionic liquid systems (i) Monte Carlo simulation techniques were employed to predict the solubility of gases and water in ionic liquids and (ii) molecular dynamics simulations were used to investigate the solvation dynamics of water and various organics in ionic liquids. ... 

In a series of papers dealing with different types of organic families, Jorgensen and his groups have developed the optimized potentials for liquid simulation (OPLS), a force field construction accurately calibrated to reproduce the structure and energetics of organic liquids in Monte Carlo simulations these are reviewed in Section 9.5.2. Another attempt at deriving an empirical force field for molecules in isolation and in condensed phases has been presented by Sun [27]. A compilation of parameters for force field calculations is available [28]. 

Table 9.1 Thermodynamic properties of liquid organic compounds from early Monte Carlo simulations. Data at ambient conditions unless otherwise stated. Refs [13-18]...

Thermal expansion coefficients can be easily estimated by running molecular dynamics or Monte Carlo simulations, yielding molar volumes as a function of temperature, a complete equation of state for the considwed material (as was shown in Fig. 9.6 notice there the significant difference in steepness between the curve for the solid and that for the liquid). Note however that for f) 2 x 10 " the total expansion of an organic material from zero-K crystal to its melting point is as low as 5-6%, so highly refined or ad hoc potentials may be required for accurate results (ref. [22], Chapter 9). 

Figure 5 Comparison of computed and experimental densities (g cm" ) for organic liquids. Computed results are from Monte Carlo simulations with the OPLS-AA force field...

A complete set of intermolecular potential functions has been developed for use in computer simulations of proteins in their native environment. Parameters have been reported for 25 peptide residues as well as the common neutral and charged terminal groups. The potential functions have the simple Coulomb plus Lennard-Jones form and are compatible with the widely used models for water, TIP4P, TIP3P and SPC. The parameters were obtained and tested primarily in conjunction with Monte Carlo statistical mechanics simulations of 36 pure organic liquids and numerous aqueous solutions of organic ions representative of subunits in the side chains and backbones of proteins... 

This chapter is organized as follows. In section 1.1, we introduce our notation and present the details of the molecular and mesoscale simulations the expanded ensemble-density of states Monte Carlo method,and the evolution equation for the tensor order parameter [5]. The results of both approaches are presented and compared in section 1.2 for the cases of one or two nanoscopic colloids immersed in a confined liquid crystal. Here the emphasis is on the calculation of the effective interaction (i.e. potential of mean force) for the nanoparticles, and also in assessing the agreement between the defect structures found by the two approaches. In section 1.3 we apply the mesoscopic theory to a model LC-based sensor and analyze the domain coarsening process by monitoring the equal-time correlation function for the tensor order parameter, as a function of the concentration of adsorbed nanocolloids. We present our conclusions in Section 1.4. 

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