Non-bonded contributions

Atomistically detailed models account for all atoms. The force field contains additive contributions specified in tenns of bond lengtlis, bond angles, torsional angles and possible crosstenns. It also includes non-bonded contributions as tire sum of van der Waals interactions, often described by Lennard-Jones potentials, and Coulomb interactions. Atomistic simulations are successfully used to predict tire transport properties of small molecules in glassy polymers, to calculate elastic moduli and to study plastic defonnation and local motion in quasi-static simulations [fy7, ( ]. The atomistic models are also useful to interiDret scattering data [fyl] and NMR measurements [70] in tenns of local order. 

The use of a cut-off distance reduces the fonnal scaling in the large system limit from atom - atoni since the non-bonded contributions now only are evaluated within the locSl sphere determined by the cut-off radius. However, a cut-off distance of 10 A is so large that the large system limit is not achieved in practical calculations. The actual scaling is thus more like where n is perhaps 1.5-1.8. In static applications,... 

The effective dielectric constant e can be included to model the effect of surrounding molecules (solvent) and the fact that interactions between distant sites may be through part of the same molecule, i.e. a polarization effect. A value of 1 for e should the dividing line be Most force fields include vdw/ ei foi" atom pairs which are separated by three bonds or more, although interactions which are 1,4 in many cases are scaled down by a factor of between 1 and 2. This means that the rotational profile for an A-B-C-D sequence is determined both by tors and vdw/ ei terms for the A-D pair. In a sense Etors may be considered as a correction necessary for obtaining the correct rotational profile once the non-bonded contribution has been accounted for. Some force... 

The use of a cut-off distance reduces the formal scaling in the large system limit from atom atom since the non-bonded contributions now only are evaluated within the... 

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