The Dispersion Energy Problem

In reviewing the performance of density functional theory applied to hydrogen bonded complexes of moderate strength, we repeatedly noted a systematic underestimation of the interaction energies for many types of functionals, usually below 2 kcal/mol. This has been related by some researchers to the inability of modem functionals to describe those contributions to intermolecular binding energies which stem from dispersion forces. Dispersion 

57 Searching the Chemical Abstracts database for the combined keywords DFT and hydrogen bond reveals 201 entries for the time between January 1997 and August 1999. 

Jeong and Han, 1996, Ruiz, Salahub, and Vela, 1996, Meijer and Sprik, 

however, that the 1999 Nobel Prize for Chemistry was awarded to A. Zewail for his studies of die transition states of chemical reactions using femtosecond spectroscopy (Academy s citation, October 12, 1999). 

In particular, reactions involving transition-metals have attracted a lot of interest recently because of the connection to catalytic and enzymatic processes. Unfortunately, the proper computational description of such reactions is one of the great challenges of today s theoretical chemistry and the question for the general applicability of density functional methods in the field is an area of active research. We chose to provide a single but - as we think - representative example to illustrate the difficulties one has to face in theoretical studies of transition-metal reactivity. 

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