Evaluation of small Gaussian basis sets for ab-initio calculations on biologically active molecules

(5s, 2p) and (7s, 4p) Gaussian basis sets are presented and evaluated for first- and second-row atoms, respectively, appearing in biologically active molecules. The exponents of the valence shell primitives are taken from larger bases, where the valence shell is better represented, in order to avoid the overemphasis on the core, which occurs in small bases when all exponents are optimized. Contraction coefficients are given for constructing double zeta and minimum molecular basis sets. The basis sets are evaluated by applying them to 19 molecules containing first- or second-row atoms. The results indicate that they are competitive with larger bases for the calculation of properties mainly dependent on the valence shell electrons. In particular, proton affinities seem to be quite reliably reproduced so that they can be used for investigations involving reaction or interaction with proton donors.