Computing the heat of formation for cubane and tetrahedrane with density functional theory and complete basis set ab initio methods

The evaluation of three commonly used density functional methods for computing heats of formation for tetrahedrane and cubane were performed. Heats of formation were computed from the total energies of these two strained hydrocarbons and building elements (carbon and hydrogen molecule), with the experimental carbon heat of formation given (169.9 kcal/mol). It was demonstrated that the complete basis set ab initio method computes heats of formation that are very close to the experimental, as well as G2 values. Hybrid density functional theory computes almost identical values and it is recommended as method of choice for computing heats of formation, while local spin density approximation generates energies that are few hundred kcal/mol away from the experimental value and should be avoided for these calculations. (C) 2000 Elsevier Science B.V. All rights reserved.