Potential functions for hydrogen bond interactions. II. Formulation of an empirical potential function

Abstract

This part describes the method of testing against the observed distribution of the parameters R, the N...O distance, and θ , the angle NH...O, of the modified Lippincott-Schroeder potential function discussed in Part I (ref. 1) and gives details of the test and the values of the discrepancy indices for a variety of conditions. Over the range of interest of (R,θ) in which hydrogen bonds occur, the variation ΔV = V - V_min of the potential function with R and θ can be expressed by a simple empirical expression in terms of Δ(= R - R_min) and θ, containing five constants, of which one does not change appreciably. The values of these constants corresponding to best agreement with observation have been obtained. An interpolation method, using cubic expressions in R and in θ, by which a smooth transition is obtained from the hydrogen bond function, V_hb, in the range in which it is valid, to the nonbonded function V_nb, valid for large R, is also described.