Monte Carlo simulation disorder

Figure 6 shows the field dependence of hole mobiUty for TAPC-doped bisphenol A polycarbonate at various temperatures (37). The mobilities decrease with increasing field at low fields. At high fields, a log oc relationship is observed. The experimental results can be reproduced by Monte Carlo simulation, shown by soHd lines in Figure 6. The model predicts that the high field mobiUty follows the following equation (37) where d = a/kT (p is the width of the Gaussian distribution density of states), Z is a parameter that characterizes the degree of positional disorder, E is the electric field, is a prefactor mobihty, and Cis an empirical constant given as 2.9 X lO " (cm/V). ...

Based on the Monte Carlo simulations, it is seen that the presence of positional disorder causes the mobiUty to decrease with increasing field at low fields (37). This is the case because the introduction of positional disorder into the system provides the carrier with energetically more favorable routes, which occasionally are against the field direction. These detour routes are most efficient at low fields, but are eliminated at high fields. This rationalizes the decrease of hole mobilities with increasing field. 

Stadler et al. [150,151] have performed Monte Carlo simulations of this model at constant pressure and calculated the phase behavior for various different head sizes. It turns out to be amazingly rich. The phase diagram for chain length N = 1 and heads of size 1.2cr (cr being the diameter of the tail beads) is shown in Fig. 8. A disordered expanded phase is found as well as... 

Those Warren-Cowley parameters have been determined in situ above the order-disorder transition temperature by diffuse neutron scattering. From these experimentally determined static correlations, the first nine effective pair interactions have been deduced using inverse Monte Carlo simulations. 

In general, percolation is one of the principal tools to analyze disordered media. It has been used extensively to study, for example, random electrical networks, diffusion in disordered media, or phase transitions. Percolation models usually require approximate solution methods such as Monte Carlo simulations, series expansions, and phenomenological renormalization [16]. While some exact results are known (for the Bethe lattice, for instance), they are very rare because of the complexity of the problem. Monte Carlo simulations are very versatile but lack the accuracy of the other methods. The above solution methods were employed in determining the critical exponents given in the following section. 

Chandler, R. E. Houtepen, A. J. Nelson, J. Vanmaekelbergh D. 2007. Electron transport in quantum dot solids Monte Carlo simulations of the effects of shell filling, Coulomb repulsions, and site disorder. Phys. Rev. B 75 085325-085335. 

Fig. 18. Phase diagram of the centered rectangular lattice gas model with ==0, 3/4 2 = V3> vJ

Bassler H (1993) Charge transport in disordered organic photoconductors - a Monte-Carlo simulation study. Phys Status Solidi B 175 15... 

Wolf U, Arkhipov VI, Bassler H (1999) Current injection from a metal to a disordered hopping system. I. Monte Carlo simulation. Phys Rev B 59 7507... 

The long-time balance between recombination and drift of carriers as expressed by the y/n ratio has been analyzed using a Monte Carlo simulation technique and shown to be independent of disorder [40]. Consequently, the Langevin formalism would be expected to obey recombination in disordered molecular systems as well. However, the time evolution of y is of crucial importance if the ultimate recombination event proceeds on the time scale comparable with that of carrier pair dissociation (Tc/Td l). The recombination rate constant becomes then capture—rather than diffusion-con-trolled, so that Thomson-like model would be more adequate than Langevin-type formalism for the description of the recombination process (cf. Sec. 5.4). 

Tapia and Eklund (1986) carried out a Monte Carlo simulation of the substrate channel of liver alcohol dehydrogenase, based on the X-ray diffraction structure for this enzyme. The addition of substrate and the associated conformation change induce an order—disorder transition for the solvent in the channel. A solvent network, connecting the active-site zinc ion and the protein surface, may provide the basis for a proton relay system. A molecular dynamics simulation of carbonic anhydrase showed two proton relay networks connecting the active-site zinc atom to the surrounding solvent (Vedani et ai, 1989). They remain intact when the substrate, HCOf, is bound. 

In the current paper, we discuss some of the new approaches and results that have been developed and obtained recently within the context of such molecular modeling research, and in particular with the mean field and Monte Carlo studies of a lattice model. The next section describes the Gaussian random field method (Woo et al, 2001), which provides a computationally efficient route to generate realistic representations of the disordered mesoporous glasses. Application of the mean field theory, and Monte Carlo simulations are described in Secs. 3 and 4, respectively. 

A grand canonical Monte Carlo simulation study of water adsorption in a Vycor-like disordered mesoporous material at 300 K. 

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