Correlation Consistent Basis Sets and Core Polarization Potentials for Al–Ar with ccECP Pseudopotentials

New correlation consistent basis sets for the second-row
atoms
(Al–Ar) to be used with the neon-core correlation consistent
effective core potentials (ccECPs) have been developed. The basis
sets, denoted cc-pV­(n+d)­Z-ccECP (n = D, T, Q), include the “tight”-d functions that are
known to be important for second-row elements. Sets augmented with
additional diffuse functions are also reported. Effective core polarization
potentials (CPPs) to account for the effect of core–valence
correlation have been adjusted for the same elements, and two different
forms of the CPP cutoff function have been analyzed. The accuracy
of both the basis sets and the CPPs is assessed through benchmark
calculations at the coupled-cluster level of theory for atomic and
molecular properties. Agreement with all-electron results is much
improved relative to the basis sets that originally accompanied the
ccECPs; moreover, the combination of cc-pV­(n+d)­Z-ccECP
and CPPs is found to be a computationally efficient and accurate alternative
to including core electrons in the correlation treatment.