PCFF force field

PCFF force fields, alternatively with molecular dynamics, in order to identify the global minimum of the energy value). The investigated single chain has a polymerization degree DP=25, similar to the results obtained by synthesis. 

FIG. 3 C33 axial modulus of polyethylene obtained using different force fields and computational methods. All calculations are classical. Open symbols are from optimizations (circles, triangles, and diamond are self-consistent QHA lattice dynamics, all others are plotted at temperature of experimental lattice parameters potential energy minimizations are plotted at OK). Filled symbols are Monte Carlo (circles) or molecular dynamics (diamond, triangles). Force field of Ref. 55 open and filled circles (from Ref. 46) force field of Ref. 30 open (from Ref. 33) and filled (from Ref. 68) triangles pcff force field of Biosym/MSI open and filled diamonds (from Ref. 66) x (from Ref. 42) -I- (from Ref. 43) open inverted triangle (from Ref. 44) open square (from Ref. 29). Curves are drawn as guides to the eye. 

Comparison of Diffusivity Values for Butane in Silicalite Using UA and PCFF Force Fields... 

Symbol UA Force Field PCFF Force Field Experimental... 

In our calculations, we used the PCFF force field,which has the form... 

FIGURE 4.1 Component terms in the PCFF force field. 

Ab Initio force field CFF91-CZEO, PCFF Force field for zeolite frameworks 25, 26, 29 31, 32 Adsorption and diffusion of hydrocarbons in zeolites Structure and spectra of silica and aluminum-phosphates 30... 

As an illustration, we have reproduced the results for the diffusivity of methane in a silicalite by using the UA potentials (Leroy et al. 2004). We then used a better and a more detailed force field polymer consistent force field (PCFF) to compute the diffusivity of butane in silicalite. We see that the PCFF description of the problem yields results closer to experiments. 

We chose to model the zeolite with only the oxygen atoms in it at the appropriate positions in the zeolite geometry. As described before, methane was modeled using the UA potential, whereas we chose to model butane using the PCFF description (Hill and Sauer 1994). The interaction parameters of the UA force field are shown in Table 10.1. 

Force field parameters for inorganic constituents have been a major hurdle in the quantitative analysis of interfaces in nanocomposites while energy models for surfactants, polymers, and biopolymers have been developed in sufficient reliability to simulate densities, cohesive energies, and interface energies. At the classical atomistic level, several force fields are in use, such as AMBER [50], CHARMM [51], CVFF [52], COMPASS [53], OPLS-AA [54], PCFF [55], and UFF [56]. For example, the energy expressions of CVFF [52], and PCFF [55] (same as COMPASS [53]), are as follows ... 

In brief, we have described a physical basis for a new generation of force fields that encompass inorganic, organic, and biomolecular constituents on a common modeling platform. To date, accurate models for layered silicates (mica, montmorillonite, and pyrophyllite) [57] and fee metals (Ag, Al, Au, Cu, Ni, Pb, Pd, and Pt) [61] are available for quantitative simulation of nanocomposites using material-oriented (extended CVFF, extended PCFF) and biologically oriented force fields. 

In conclusion, to assign the absolute configuration of a primary alcohol by this method, a preliminary calculation must be performed (being the best force field, PCff), especially when the chiral center is part of a ring, or when strong steric interactions could be in operation, to confirm that the anti form is the most... 

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