The resolution of the identity approximation applied to the correlation consistent composite approach.

A new implementation of the correlation consistent composite approach (ccCA), denoted RI-ccCA, utilizing both the resolution of the identity (RI) and local methods is presented. A set of 102 molecules composed of first and second row, main group atoms is employed to compare total energies, atomization energies, and enthalpies of formation between the original ccCA implementation and those of RI-ccCA. Relative CPU time and disk space requirements of RI-ccCA as compared to ccCA, demonstrate that on the average, employing the RI approximation in ccCA affords CPU time savings over 70% and disk space requirements diminished by well over 90% without introducing significant error in energetic properties.