- The effect of electron correlation on the electron distribution and bonding of diborane is examined in several basis sets. The generalized molecular orbital method is used to define optimized orbitals for the configuration interaction calculations. The results indicate that at least double-f (two functions per atomic orbital) and polarization functions (d functions on B and p functions on H) are needed to adequately describe the electron density of diborane. Electron correlation shifts electron density away from the hydrogens, both terminal and bridging, and into the interior of the cluster and increases the direct B-B contribution to the bonding. We have also calculated the dissociation energy of diborane (B2H6 2BH3). The experimental value is 35 kcal/mol, while without electron correlation the theoretical value is only about 20 kcal/mol. Thus, electron correlation increases the stability of the cluster by about 15 kcal/mol. Our results suggest that the substantial effect of electron correlation on the bonding of diborane is a general result and will apply to other cluster systems. 1980, American Chemical Society. All rights reserved.