Configurational bias Monte Carlo CBMC

The value of S(Q) at zero Q value cannot be determined experimentally on the same instrument that is used to measure diffusivities there are not enough points at small Q in Fig. 8b. However, the S(Q) scale, which is given in Fig. 8b in arbitrary units, can be renormalized. At infinite dilution, S(0) should be equal to one (hke in a gas), and sorption thermodynamics also imply that the thermodynamic correction factor should be equal to one, so that Eq. 38 will be fulfilled. On the other hand, at high concentrations, F increases while S(0) goes down. In Fig. 8b, r is equal to 6.6 for a concentration of 14 CF4 per u.c. so that S(0) should go down to 0.15. A more quantitative analysis has been recently performed for n-hexane and n-heptane in sihcalite [36] where the inverse of the thermodynamic factor, calculated from S(Q) was found to be in good agreement with configurational-bias Monte Carlo (CBMC) simulations. 

For symmetric generation probabilities like in equation 6.16 the factors Pg (o —> n) and Pg (u —> o) cancel. However, one can construct trial moves for which Pg (o —> n) Pg (n —> o). A well-known example of such a trial move is Configurational-Bias Monte Carlo (CBMC, see chapter 2). This can, for example, be used to change the orientation of the tail of a long branched molecule like 2-methylpentane, as such a reorientation will not be observed on the time-scales of MD in a narrow channel of a zeolite. It is important to note that one is able to construct many variations of the shooting trial move, for example, one can use rotation moves or choose the time t with a bias. However, one has to ascertain that the new configuration at time t does not differ too much from the old configuration at t because otherwise the new path will not start in A or end in B. 

CBMC = configurational bias Monte Carlo DEM = diffusion equation method LES = locally enhanced sampling QMA = quantum mechanical annealing. 

CBMC configurational-bias Monte Carlo EDXRD... 

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