Interaction potentials parameters

The energetic inhomogeneity of the surface along the x and y directions is not taken into account, but this is not expected to affect the results significantly at 308 and 333 K [39]. The cross interaction potential parameters between different sites were calculated according to the Lorentz-Berthelot rules Oap = aa + and eafi= ( The potential energy t/ due to the walls inside the slit pore model for each atom of the CO2 molecule is given by the expression C/ = + Uw(H-r where H is the distance between the carbon centers across... 

Cambi, R., Cappelletti, D., Liuti, G., and Pirani, F. (1991) Generalized correlations in terms of polarizability for van der Waals interaction potential parameter calculations. J. Chem. Phys., 95, 1852-1861. 

In Older to be able to perform effective characterization it is crucial to use appropriate interaction potentials. Parameters for fluid-fluid interaction potentials have been studied extensively and in the present work were taken from the literature. The solid-fluid interaction potential i rameters were calibrated separately for each material ttonsidered. The calibration procedure consists of the following steps [8] ... 

The MSI Cerius2 3.8 software package was used to study physical sorption of N2 and O2 on LiLSX zeolite as function of pressure of the sorbing species. Calculations are based on the application of a Monte Carlo simulation algorithm in the Grand Canonical Ensemble [58,59]. The interaction-potential parameters used in the forcefield expression of this investigation are published in [60], together with details of the simulation setup. 

Figure 19-8. Measured second virial coefficients ofSTA (soUd squares) in dffferent background salt concentrations compared with data on a number of proteins (Lysotyme, BPTI open circles) in different buffer solutions. The second virial coefficients are nondimensionalized with the hard sphere value and plotted against the solubility (volume fraction 0at) of the respective species. The solid lines are calculations of the attractive Yukawa potential with two different ranges of attractions (2ak) of 7 and 15. The values of 7 and 15 indicate that attractions between the particles are short ranged. The experimental datafor STA (at high salt concentrations) and proteins collapse within the narrow range of attractions which are only a fraction of the particle diameter. The collapse also indicates thatproteins and STA are thermodynamically similar, iftwo suspensions have the same B2 then they have the same solubility. This plot also provides an opportunity to extract interaction potential parameters for a given experimental system in a model independent manner. For detailed discussions, please refer to (Ramakrishnan, 2000).

Figure 7. Phase diagrams of bulk sample of OPS in space of pair interaction potentials parameters (a) -van der Waals potential (4.1), (b) - pseudopotential approximation (4.5).

Alternatively, the relation between structure and conductivity in both ordered and disordered compounds can be investigated using molecular dynamics (MD) simulations. In principle, MD simulations will lead to comprehensive structural and dynamic informatimi within the limitations imposed by the system size, the simulated period, and the agreement of the employed interaction potential parameters with reality. Both diffraction data (crystal structures for crystalline compounds, RMC fits for glasses) and MD approaches are valuable tools to obtain insight into the conductimi mechanism and its correlation to the atomic stmcture, though in the case of MD simulatimis it has to be verified that the force field chosen for the simulations leads to structure models that are cmisistent with experimental information. 

There are many large molecules whose mteractions we have little hope of detemiining in detail. In these cases we turn to models based on simple mathematical representations of the interaction potential with empirically detemiined parameters. Even for smaller molecules where a detailed interaction potential has been obtained by an ab initio calculation or by a numerical inversion of experimental data, it is usefid to fit the calculated points to a functional fomi which then serves as a computationally inexpensive interpolation and extrapolation tool for use in fiirtlier work such as molecular simulation studies or predictive scattering computations. There are a very large number of such models in use, and only a small sample is considered here. The most frequently used simple spherical models are described in section Al.5.5.1 and some of the more common elaborate models are discussed in section A 1.5.5.2. section Al.5.5.3 and section Al.5.5.4. 

The packing energy of an organic crystal can be easily calculated by a lattice sum over pairwise interactions. The potential parameters for these calculations are summarized in Table 15. The packing energy is usually a quite accurate estimate of the crystal sublimation energy. 

According to Hess, the relative strength of the entanglement friction can be related to the more microscopic parameter q , describing the range of the true interchain interaction potential. A value of q 1 = 7 A, close to the average interchain distance of about 4.7 A, is obtained. 

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