Ab initio calculations are used to test the ability of various representations to reproduce bond energies. It is found that expansion in 1/R, where R is the bond length, is remarkably efficient and is consistently better than the usual R expansion. A quadratic form in 1/R is better than a cubic representation in R and sometimes even as good as a quartic representation. A cubic function in 1/R is, in all cases studied, better performing than the quartic expansion in R. It is also found that parameters derived with the 1/R expansion are defined more sharply than those derived for the R expansion. It is suggested that the 1/R expansion may be computationally more efficient for simulations of large biomolecules and for constructions of reactive force fields than the standard bond functions. © 1994 by John Wiley & Sons, Inc.