Gradient fit functions for two-body potential energy surfaces based upon a harmonic series.

While force-field development has been discussed extensively in the literature, the question of what analytical expressions make the best function choices, particularly in the context of matching quantum mechanic potential energy surfaces (PES), is less explored. Traditional forms based upon harmonic oscillators and Lennard-Jones types have dominated the field owing to the focus on fitting properties. However, with the advent of gradient-fitting approaches, it is now possible with the correct force-field expressions to achieve consistent high-accuracy results with molecular dynamics calculations. Using the general principle that power series can fit surfaces of any shape well, we have utilised harmonic series functions to fit a two-body PES represented by a Morse function. The harmonic functions are fast because they have only integer exponents, and they fit accurately with a limited number of terms. [ABSTRACT FROM AUTHOR]