A MODIFICATION OF THE TANG-TOENNIES POTENTIAL MODEL TO PRODUCE A MORE REALISTIC REPULSIVE WALL - APPLICATION TO HE-2

Tang and Toennies presented [1] a simple model potential with individual damping for spherical interactions. Their model enables one to predict the interaction from only a knowledge of the dispersion coefficients and well known values for the energy and length parameters-epsilon and r(m). While this scheme results in a realistic representation of the potential bowl and long-range tail, the repulsive wall of the model is, unfortunately, generally too stiff. In the case of helium, the ab initia dispersion coefficients are accurately known, and hence the potential model contains no adjustable parameters to rectify this problem. In this work we present a modification of their model potential which includes two additional parameters to provide for improved flexibility. This new version of the model yields a more accurate representation of the helium system over a much larger range of interatomic separations than the original model.