Density functional calculations of molecular bond energies

The calculation of molecular bond energies is a sensitive test of exchange-correlation approximations in density functional theory. The well known local density approximation (LDA) gives excellent bond lengths and vibrational frequencies, but seriously overestimates dissociation energies. Therefore, we have investigated the effect on bond energies of nonlocal corrections to the LDA exchange-correlation functional. We consider the nonlocal correction term of Langreth and Mehl, and also a new semiempirical exchange energy correction. Significant improvements over the LDA dissociation energies are obtained in calculations on first-, second-, and third-row homonuclear diatomic systems.