Comparison of models to correlate electron density at the bond critical point and bond distance

Two models proposed in the literature to correlate the electron density at the bond critical point with the bond distance have been compared. The first one, proposed independently by Knop-Boyd and Destro, considers an implicit double logarithmic relationship between these two properties. We propose a second model, which uses a logarithmic relationship. Van der Waals and hydrogen bond interactions as well as traditional covalent bonds have been considered in order to have a broader range of the compared properties. The results indicate that both models provide good results when individual bond types are correlated, although the logarithmic model seems to be slightly better than the double logarithmic one. Finally, a unique equation corresponding to model 2 has been devised to correlate all the H-X or C-X bonds. (C) 2000 Elsevier Science B.V. All rights reserved.