Nonbonded Scale Factors

BIO-h and OPLS scale 1 van der Waals and 1 electrostatic interactions. Although the value of the 1 nonbonded scale factors is an option in HyperChem, you should generally use recommended values. This is because during parameterization, the force field developers used particular values for the 1 nonbonded scale factors, and their parameters may not be correct for other scale factors. 

The van der Waals scale factors used during force field parameterization are 0.5 for AMBER, 1.0 for BlO-t, and 0.125 for OPLS. Eor 1-4 electrostatic interactions, use 0.5 for AMBER, BlO-t, and OPLS. 

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Although interactions between vicinal atoms are nominally treated as nonbonded interactions, most of the force fields treat these somewhat differently from normal 1-5 and greater nonbonded interactions. HyperChem allows each of these nonbonded interactions to be scaled down by a scale factor <1.0 with AMBER or OPLS. For BlO-t the electrostatic may be scaled and different parameters may be used for 1 van der Waals interactions. Th e AMBER force field, for exam p le, norm ally u ses a scalin g factor of 0.5 for both van der Waals and electrostatic interactions. 

Dg is the well depth, r and rg the current and equilibrium interatomic distances, respectively, y is a scaling factor, and B, p, tj, c , and are potential parameters. These nonbonded interaction forms are employed by Cerius, version 3.9 (Ref. 64). 

During the OPLS energy calculations, all 1-4 nonbonded interaction energies were scaled down by a factor of two. However, it.was noted that this common practice could lead to an unbalanced treatment of interatomic interactions, some of which are particularly relevant to carbohydrates. ... 

To separate the nonbonded forces into near, medium, and far zones, pair distance separations are used for the van der Waals forces, and box separations are used for the electrostatic forces in the Fast Multipole Method, since the box separation is a more convenient breakup in the FMM method. Using these subdivisions of the force, the propagator can be factorized according to the different intrinsic time-scales of the various components of the force. 

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