It is noticed that inclusion of an electrostatic term in the molecular-mechanical treatment of hydrocarbons would compel the nonbonding parameters of different force fields to become more alike than they are at present. Apart from removing the discontinuity in passing from the calculation of an unfunctionalized parent compound to the calculation of its functionalized derivatives, it is expected that the inclusion would improve results for the hydrocarbons themselves.
A considerable number of well-established force fields serves currently for molecular-mechanical calculations.' Additional fields are used in certain laboratories for specific ends. This variety has the drawback that results from different sources are not readily comparable and that the meaningfulness of the force field process becomes obscured. On comparing force fields, one finds a multitude of small differences, along with a marked divergence in the evaluation of nonbonded interactions2y3 (En,,). Not only does the formulation of this contribution to the molecular energy differ from one field to another, but so also do the numerical constants that intervene. And yet, these parameters ( r * , E ) are meant to represent entities that are liable to physical interpretation, namely, the size and hardness of atoms. In this report, we note that inclusion of electrostatic interaction may restrict the latitude of choice as to r* and E, without affecting other components in a given field. This inclusion should help to render separate force fields more similar to each other than they are now. It is also expected that the constants within each of the extant force fields become more highly transferable than they are.
At present, admittedly, there are no pressing grounds for a radical change in the treatment of hydrocarbons. The problem is essentially of elegance, in the sense that one category of force fields (without electrostatics) is being used for hydrocarbons, and another category (with electrostatics) is being used for their derivatives. One