Atomistic simulation experimental agreement

Then an important aspect is how precise the predicted D will be So far an agreement within one order of magnitude between an experiment and an atomistic simulation is considered to be a good achievement. For completely amorphous polymer structures and simple penetrants even better agreements have been reported in Tables 5-1 and 5-2. From the point of view of estimating the migration from polymeric materials used in the technical sector a prediction of D within the order of magnitude of the experimental one would be a result of certain practical use, see Chapter 15. The question is to what sophistication must be developed the computer simulation approach to meet this requirement also for the type of penetrant polymer systems which are usual in the named sector ... 

Another application of atomistic simulations is reported by De Pablo, Laso, and Suter. Novel simulations for the calculation of the chemical potential and for the simulation of phase equilibrium in systems of chain molecules are reported. The methods are applied to simulate Henry s constants and solubility of linear alkanes in polyethylene. The results seem to be in good agreement with experiment. At moderate pressures, however, the solubility of an alkane in polyethylene exhibits strong deviations from ideal behavior. Henry s law becomes inapplicable in these cases. Solubility simulations reproduce the experimentally observed saturation of polyethylene by the alkane. For low concentrations of the solute, the simulations reveal the presence of pockets in the polymer in which solubility occurs preferentially. At higher concentrations, the distribution of the solute in the polymer becomes relatively uniform. 

The d3mamical behavior of the cyanide ion (CN ) has been well studied experimentally [138-140]. Atomistic simulations have shown to give energy relaxation times in good agreement with experiments [49, 141]. It has been found that vibrational energy relaxation is particularly sensitive to the level at which the... 

Atomistic simulation has also been carried out to calculate electric properties of PVDF Two force fields, MSXX and MSXXS, were specifically built up to address this issue [49]. Dielectric constants and dielectric loss were thus computed for both the crystalline and amorphous phases of PVDF. In agreement with experimental data, the ensuing computational results showed that the amorphous phase exhibits a higher dielectric constant than the crystalline phase. This behavior arises fi om rapid changes in the torsion angles, leading to rapid modulation of the dipole moment perpendicular to the chain axis. It is stimulated by the presence of sohton-like defects that diffuse along the chain, as it was revealed by MD simulation [49]. 

As announced above these findings are in astonishing agreement with the heuristic pictures of the diffusion mechanism discussed in the framework of some microscopic diffusion models. But, besides being free of the conceptual drawbacks (the ad hoc assumptions) of the classical diffusion models, the MD method of computer simulation of diffusion in polymers makes it possible to get an even closer look at the diffusion mechanism and explain from a true atomistic level well known experimental findings. For example the results reported in (119,120) on the hopping mechanism reveal the following additional features. 

Overall, the results from the cathode-only KMC simulations [118-120] were found to be qualitatively consistent with experimental trends, with a great deal of the atomistic-level details preserved. However, in order to improve the results, and approach quantitative agreement with experiments, additional features must be incorporated, such as the anode-side reactions, correlation of the ion-vacancy and vacancy-vacancy interactions, grain boundaries, and explicit structural treatment of the anode and cathode. In order to incorporate some of these necessary features, two KMC-based SOFC simulation studies have recently emerged [126,127] along with some close experimental collaboration [128], In all of these more recent studies, a complete SOFC model (anode+cathode) was assembled. 

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