A semiempirical molecular-orbital approach has been developed to calculate the atomization energies of 117 small molecules containing hydrogen, carbon, nitrogen, oxygen and fluorine. The molecules were mostly organic. Ten parameter sets were used to account for the hybridizations of the atoms of these five elements with single bonds (5 sets), with double bonds (3 sets) and with triple bonds (2 sets). One-electron energies with Slater orbitals were used with separate values of Z2S and Z2P. Calculations were made with a CNDO/INDO Fortran 77 program modified to a level of approximation that is more similar to an extended Hückel calculation rather than to a CNDO or INDO calculation. A repulsion work function was used in this work to calculate repulsion energies between pairs of atoms within each molecule. The correlation between calculated and experimental 117 atomization energies was favourable with a standard deviation of 0.39 eV. The standard deviation between calculated and experimental dipole moments of nine diatomic molecules was 0.04 debye. This semiempirical method gave favourable results for nicotine and caffeine molecules compared to the results of DFT calculations. The calculations in the present work for all 119 molecules were performed in double precision on a 64-bit personal computer within one second.
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