Quasi-random structures

NON SELF-CONSISTENT THEORIES A. The Quasi-Random Structure Method... 

This methodology, which is also called SQS (for special quasi-random structures) has been extended to incorporate volume effects and other physical features entering the description of an alloy, such as charge-transfer effects. 

Fig. 4. A schematic two-dimensional illustration of the idea for an information theory model of hydrophobic hydration. Direct insertion of a solute of substantial size (the larger circle) will be impractical. For smaller solutes (the smaller circles) the situation is tractable a successful insertion is found, for example, in the upper panel on the right. For either the small or the large solute, statistical information can be collected that leads to reasonable but approximate models of the hydration free energy, Eq. (7). An important issue is that the solvent configurations (here, the point sets) are supplied by simulation or X-ray or neutron scattering experiments. Therefore, solvent structural assumptions can be avoided to some degree. The point set for the upper panel is obtained by pseudo-random-number generation so the correct inference would be of a Poisson distribution of points and = kTpv where v is the van der Waals volume of the solute. Quasi-random series were used for the bottom panel so those inferences should be different. See Pratt et al. (1999).

In this paper, we studied the glass transition and the localization-delocalization transition in a disparate-size hard-sphere mixture from a dynamical viewpoint. For Cl = 0.5, the existence of the delocalized phase of the small particles is confirmed by investigating the frequency-dependent diffusion constant. Near the glass transition, we found an additional quasi-elastic structure in " q,uj) and Di(u>) at small o), which suggests that the diffusion mechanism of the small particles would change from the liquid-like diffusion to a slow diffusion in a random potential. 

These blind test results have not only identified some important limitations of the search methods that are in use for CSP but have also highlighted some methods that have been found to be reliable across the series of tests. The third and fourth blind tests highlighted structure generation methods based on simulated annealing and random or quasi-random sampling as being most consistently successful." ... 

The structural detail at the molecular level of a polymer is referred to as its microstructure. As shown in Figure 6.1a, the microstructures of HDPE, LDPE, and LLDPE are different. HDPE is a long polymer chain with very little branching. In contrast, LDPE has a lot of branching, and the branches are random and of variable lengths. Traditionally, for LLDPE, small amounts of 1-butene or 1-hexene or 1-octene are polymerized with ethylene, and these produce short branches of quasi-regular structure. 

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