GAUSSIAN-BASIS SETS FOR USE IN CORRELATED MOLECULAR CALCULATIONS .5. CORE-VALENCE BASIS-SETS FOR BORON THROUGH NEON

The correlation-consistent polarized valence basis sets (cc-pVXZ) for the atoms boron through neon have been extended to treat core and core -valence correlation effects. Basis functions were added to the existi ng cc-pVXZ sets to form correlation-consistent polarized core-valence sets (cc-pCVXZ) in the usual pattern: Double zeta added (1s1p), triple zeta added (2s2p1d), quadruple zeta added (3s3p2d1f), and quintuple z eta added (4s4p3d2f1g). The exponents of the core functions were deter mined by minimizing the difference between all-electron and valence-on ly correlation energies obtained from HF+1+2 calculations on the groun d states of the atoms. With the cc-pCVXZ sets, core, core-valence, and valence correlation energies all converge exponentially toward appare nt complete basis set (CBS) limits, as do the corresponding all-electr on singles and doubles CI energies. Several test applications of the n ew sets are presented: The first two ionization potentials of boron, t he P-3-S-5 separation in carbon, and the (X) over tilde(3)B(1)-(a) ove r tilde(1)A(1) state separation in CH2. As expected, correlation effec ts involving the core electrons of the first row atoms, B-Ne, are smal l but must be included if high accuracy is required. (C) 1995 American Institute of Physics.