Basis set effects on B3LYP geometries and energies:: Case study of interstellar reaction HN=CH2+.C≡N→H2N-C(.)H-C≡N

To facilitate a rational basis set selection for B3LYP studies of organic reactions in the interstellar medium, we analyzed energetic parameters for the main stationary points in the reaction HN=CH2 + (.)CdropN --> H2N-C((.))H-CdropN and geometric parameters for its main transition state, calculated using 25 frequently used basis sets (21 Pople's and 4 Dunning's correlation-consistent basis sets). For the energy estimates, one can recommend the 6-31+G(d,p) basis set, or at most 6-311G(d,p). Adding more polarization and including diffuse function on both heavy atoms and hydrogens do not cause substantial changes in the energies and geometric parameters such as bond lengths and angles, and cannot justify spending more computation time. The bond lengths and angles converge within 0.01 Angstrom and 1degrees, respectively, starting with 6-31G(d): This basis set can be recommended to preoptimize the geometries. (C) 2002 John Wiley Sons, Inc.