Abstract
Floating spherical Gaussian basis sets are systematically expanded for a series of small molecules: methane, ammonia, ethane, and acetylene. Localized (nonorthogonal) molecular orbitals are each constructed as a linear combination of up to five functions of the form exp [– (r – R)2/ρ2], where the size ρ and the position R of each function is optimized according to the variation principle. Basis sets are obtained for the C and N cores, the C ; H and N H bonds, the N lone pair, and the C C and CC bonds. Only three to five fully optimized functions are required to describe the main features of each bond orbital, including the negative lobes in the wavefunctions at the heavy atoms and the local maximum in the electron density at the hydrogen atoms. The energies obtained with three basis functions for the core orbitals are intermediate between the results of RHF‐SCF calculations with STO‐3G and 3‐21G basis sets.