Grain model comparison with experiment

The values of the force field parameters need to be adjusted to ensure that the coarse-grained model gives reasonable results in comparison with experiment. Tables 4, 5, and 6 show the values of C, and e obtained from the PMFs for the 210 bead-bead pairs. Here, we select the osmotic second virial coefficient (B22) of lysozyme as the reference property because it well represents the strength of lysozyme-lysozyme interactions in a solution. Lenhoff and his colleagues [41 14] measured B22 for lysozyme in a variety of solutions. Lysozyme is expected to have a positive B22 in water because it is positively charged. Their data indicate that B22 of lysozyme in water at pH 7 is around 5 x 10 mol rnl/g. ... 

This comparison between experiments and the simulation model shows that our coarse-grained model reproduces the qualitative features of hexadecane-carbon dioxide mixture. As seen in the introduction, the phase diagrams of the pure system (cf. Fig. 2) as well as the interfacial tension (cf. Fig. 5) are also in semi-quantitative agreement with the experiment. This makes the model a good starting point for investigating bubble nucleation. 

A general conclusion that can be drawn from this short survey on the many attempts to develop analytical theories to describe the phase behavior of polymer melts, polymer solutions, and polymer blends is that this is a formidable problem, which is far from a fully satisfactory solution. To gauge the accuracy of any such approaches in a particular case one needs a comparison with computer simulations that can be based on exactly the same coarse-grained model on which the analytical theory is based. In fact, none of the approaches described above can fully take into account all details of chemical bonding and local chemical structure of such multicomponent polymer systems and, hence, when the theory based on a simplified model is directly compared to experiment, agreement between theory and experiment may be fortuitous (cancellation of errors made by use of both an inadequate model and an inaccurate theory). Similarly, if disagreement between theory and experiment occurs, one does not know whether this should be attributed to the inadequacy of the model, the lack of accuracy of the theoretical treatment of the model, or both. Only the simulation can yield numerically exact results (apart from statistical errors, which can be controlled, at least in principle) on exactly the same model, which forms the basis of the analytical theory. It is precisely this reason that has made computer simulation methods so popular in recent decades [58-64]. 

Another viable method to compare experiments and theories are simulations of either the cell model with one or more infinite rods present or to take a solution of finite semi-flexible polyelectrolytes. These will of course capture all correlations and ionic finite size effects on the basis of the RPM, and are therefore a good method to check how far simple potentials will suffice to reproduce experimental results. In Sect. 4.2, we shall in particular compare simulations and results obtained with the DHHC local density functional theory to osmotic pressure data. This comparison will demonstrate to what extent the PB cell model, and furthermore the whole coarse grained RPM approach can be expected to hold, and on which level one starts to see solvation effects and other molecular details present under experimental conditions. 

A recent example is coupled T-H-M modelling of the Tunnel Sealing Experiment (TSX) in URL (Guo et al. 2002). To provide data for preliminary validation a surface laboratory experiment known as the Thermal Evaluation of Material Test (TEMT) was conducted. A steel vessel, 1.47 m long with an interior diameter of 0.74 m, was filled with a medium-grained sand and heated by circulating hot water. An array of thermistors monitored the evolution of temperature. Comparison between the physical test results and MOTIF simulation results. Figure 6, shows that MOTIF can be used to simulate convection dominated heat transfer in a porous medium. 

---