Flexible-lattice model

Simplified models for proteins are being used to predict their stmcture and the folding process. One is the lattice model where proteins are represented as self-avoiding flexible chains on lattices, and the lattice sites are occupied by the different residues (29). When only hydrophobic interactions are considered and the residues are either hydrophobic or hydrophilic, simulations have shown that, as in proteins, the stmctures with optimum energy are compact and few in number. An additional component, hydrogen bonding, has to be invoked to obtain stmctures similar to the secondary stmctures observed in nature (30). 

G. I. Menon, R. Pandit, M. Barma. Melts of semi-flexible, living polymers A lattice model. Europhys Lett 24 253-258, 1993. 

The density of states (DOS) of lattice phonons has been calculated by lattice dynamical methods [111]. The vibrational DOS of orthorhombic Ss up to about 500 cm has been determined by neutron scattering [121] and calculated by MD simulations of a flexible molecule model [118,122]. 

A lattice model of uniaxial smectics, formed by molecules with flexible tails, was recently suggested by Dowell [29]. It was shown that differences in the steric (hard-repulsive) packing of rigid cores and flexible tails - as a function of tail chain flexibility - can stabilize different types of smectic A phases. These results explain the fact that virtually all molecules that form smectic phases (with only a few exceptions [la, 4]) have one or more flexible tail chains. Furthermore, as the chain tails are shortened, the smectic phase disappears, replaced by the nematic phase (Fig. 1). 

Abstract In this review, we consider a variety of aspects of polymer crystallization using a very simple lattice model. This model has three ingredients that give it the necessary flexibility to account for many features of polymer crystallization that have been observed experimentally. These ingredients are (1) a difference in attraction between neighboring (nonbonded) components, (2) attraction between parallel bonds, and (3) temperature-dependent flexibility due to the energy cost associated with kinks in the... 

The shortcoming of this expression comes from the fact that in the Flory-Huggins lattice model, chain microstructure and real flexibility mechanisms are not taken into account. 

Silberberg47) used a quasi-crystalline lattice model for the adsorption of flexible macromolecules. If it is assumed that an adsorbed polymer chain with P segments consists of ma trains of length i and mBi loops of length i, the total number of configurations of the chains is given by... 

Cantor, R.S. Melroy, R.M. Statistical thermodynamics of flexible-chain surfactants in monolayer films. II. Calculations for a modified cubic lattice model. J. Chem. Phys. 1989, 90 (8). 4431. 

Lin and Lee started the derivation from Kantor and Webman s two dimensional model of flexible chains that considers a vectorial Born-lattice model with a bending energy term between neighboring bonds [91]. As outlined in Fig. 11, the strain energy H of a chain composed of a set of N singly connected bonds, of length a under an applied force F at the two ends of the chain is ... 

The lowering of the critical concentration of the CTA by the presence of the flexible polymer may be explained in terms of a lattice model. The large excluded volume of PMMA or PET decreases the number of lattice sites available to the semirigid CTA polymer, thus the CTA molecules are required to pack more efficiently and are more dign in the ordered phase. 

Another common theme in FP studies is the richness of possible surface phases -in some cases, dozens of structural isomers are computed to be thermodynamically accessible at room temperature. This has led to speculation that many oxide surfaces are more dynamic than previously thought, but definitive conclusions will only be possible once the processes of surface diffusion are identified and their activation energies are computed. This is perhaps the next frontier in FP oxide simulation. Meanwhile, the flexible surface model for active sites on metals [5] is finding some application in explaining the apparently facile diffusion of interstitial ions in non-stoichiometric oxides, despite the rigidity of the oxide lattice [26]. 

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