Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)The semiempirical HAM/3 molecular orbital method is used to calculate core-electron binding energies of common pyrimidine bases and some of their aza analogs. Average percent difference (error) is found to be 0.91 ± 0.12% which is substantially smaller than the error obtained from ab initio calculations with the application of Koopmans' theorem. HAM/3 chemical shifts are as good as those of ab initio direct hole state calculations reported in the literature. The molecular charge distributions calculated by HAM/3 agree fairly well with those of experiment and other theoretical methods. A large error in the HAM/3 core-electron binding energy of carbon in a CH3 group has been detected. © 1987.1503-4309317Capes-12900-13-3; CAPES; Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Lindholm, Åsbrink, Molecular Orbitals and their Energies (1985) Studied by the Semiempirical HAM Method, , Springer-Verlag, BerlinÅsbrink, Frich, Lindholm, (1977) Chem. Phys. Lett., 52, p. 63Åsbrink, Frich, Lindholm, (1977) Chem. Phys. Lett., 52, p. 69Åsbrink, Frich, Lindholm, (1977) Chem. Phys. Lett., 52, p. 72Chong, (1982) J. Mol. Sci. (Wuhan, China), 2, p. 55Siegbahn, Nordling, Fahlman, Nordberg, Hamrin, Hedman, Johansson, Linderberg, (1967) ESCA— Atomic, Molecular and Solid State Structure Studied by Means of Electron Spectroscopy, , Almqvist and Wixell, UppsalaÅshrink, Fridh, Lindholm, (1980) Q.C.P.E., 12, p. 393Peeling, Hruska, McIntyre, ESCA spectra and molecular charge distributions for some pyrimidine and purine bases (1978) Canadian Journal of Chemistry, 56, p. 1555Maksić, Rupnik, Semiempirical studies of core electron binding energies Part II. SCC-MO Calculations for uracil and its derivatives (1983) Journal of Electron Spectroscopy and Related Phenomena, 32, p. 163O'Donnell, Lebreton, Petke, Shipman, (1980) J. Phys. Chem., 84, p. 1975Dewar, Thiel, (1977) J. Am. Chem. Soc., 99, p. 4899Youmans, (1973) Statistics for Chemistry, p. 15. , Merrill, OHClark, Scanlan, Muller, (1974) Theor. Chim. Acta, 35, p. 341Stewart, (1970) J. Chem. Phys., 53, p. 205Kwiatkowski, Pullman, (1975) Adv. Heterocycl. Chem., 18, p. 199Zielinski, STO-3G study of uracil, thymine, 5-fluorouracil, 5-methoxyuracil, and their 4-hydroxytautomeric forms (1982) International Journal of Quantum Chemistry, 22, p. 639Singh, Kollman, An approach to computing electrostatic charges for molecules (1984) Journal of Computational Chemistry, 5, p. 129