Atomistic solution models

The formalism of the thermodynamics of solutions was described in Chapter 3. In this chapter we shall revisit the topic of solutions and apply statistical mechanics to relate the thermodynamic properties of solutions to atomistic models for their structure. Although we will not give a rigorous presentation of the methods of statistical mechanics, we need some elements of the theory as a background for the solution models to be treated. These elements of the theory are presented in Section 9.1. 

In simple solutions such as binary alloys, the components are distributed on a single lattice. More complex solutions may consist of two or more sub-lattices, and in a solution of simple ionic salts like NaCl and NaBr there is one sub-lattice for cations and one for anions. In these cases the interactions considered in the models are between next neighbouring pairs of atoms rather than nearest neighbour atoms, as is the case with a single lattice. Two sub-lattice models can also be applied to 

Chemical Thermodynamics of Materials by Svein St0len and Tor Grande 2004 John Wiley Sons, Ltd ISBN 0 471 492320 2 

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The whole simulations are performed according to the following procedure. First, elastic constants of PTT in amorphous phase Camor are calculated using the atomistic modeling, which will be used as input values for the matrix CP in the atomistic-continuum model. Second, elastic constants of PTT in crystalline phase CCTSt are also evaluated in the same manner as those of amorphous PTT. Third, the atomistic-continuum model is validated for heterogeneous material by comparing the calculated elastic constant for the system of infinite lamellas with its exact solution. Finally, elastic constants of semicrystalline PTT with dif-... 

Typical time scales for formation of micellar aggregates in solution are tens to hundreds of microseconds (Kositza et at, 1999). Because these time scales are much longer than those that can be covered in a simulation of an atomistically detailed model, simulation studies of self-assembly are performed using simplihed models, either in the continuum (Smit et al., 1990) or, more commonly, on lattices (Nelson et al., 1997 Xing and Mattice, 1997 Viduna et al., 1998 Girardi and Figueiredo, 2000). 

From their QSERR they find solute lipophilicity and steric properties as being responsible for analyte retention (k ) while enantioseparation (a) varied mainly with electronic and steric properties. The main difference between the analytes is that the enantioseparation of the esters is correlated with steric parameters that scale linearly with log a while the sulfoxides scale nonlinearly (parabolic), but this may be due to a computational artifact. The 3D-QSERR derived from field analysis revealed that while superpositioning of field maps for both analytes are not exactly the same, a similar balance of physicochemical forces involved in the chiral recognition process are at play for both sets of analyes. This type of atomistic molecular modeling, then, is a powerful adjunct to the type of modeling described earlier in this chapter and will, no doubt, be used more frequently in future studies. 

D. Hofmaim, L. Fritz, J. Ulbrich, C. Schepers, M. Boehning, Detailed atomistic molecular modeling of small molecule diffusion and solution processes in polymeric membrane materials, Macromol. Theory Simul., 9, 293-327 (2000). 

In (6), e is the dielectric constant of the atomistic water model and Fsr denotes the short range part of the potential which includes effects of dispersion interactions and ion hydration. It could be shown that the effective two-body potential in equation (6) reproduces the osmotic coefficients of aqueous sodium chloride solutions in satisfactory agreement with experiments up to almost 3 M salt [75]. The idea of... 

Two macromolecular computational problems are considered (i) the atomistic modeling of bulk condensed polymer phases and their inherent non-vectorizability, and (ii) the determination of the partition coefficient of polymer chains between bulk solution and cylindrical pores. In connection with the atomistic modeling problem, an algorithm is introduced and discussed (Modified Superbox Algorithm) for the efficient determination of significantly interacting atom pairs in systems with spatially periodic boundaries of the shape of a general parallelepiped (triclinic systems). 

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