where the basis-set specific constant β has values of 2.40 (DZ-TZ) or 2.97 (TZ-QZ), respectively. The resulting energies E CCS (CBS) and E C (CBS) were added together to obtain the excited-state total energies. These were then used to calculate the interaction energies at the CBS level. Ideally, the basis sets used in such extrapolations should be as large as technically possible. For CCSDR(3), only DZ and TZ calculations were feasible for the benzene dimer, while TZ and QZ calculations were possible for SCS-CC2. The resulting CCSDR(3)/CBS(2,3) interaction energies for the same four select intermolecular distances discussed for CCSDR(3)/def2-TZVP in the previous section are shown in Fig. (numerical values in Table † ) alongside the SCS-CC2 curves with truncated Ahlrichs basis sets and CBS (3,4). SCS-CC2/CBS interaction energies are slightly more negative than CCSDR(3)/CBS for three of the four points with the differences ranging from 0.34 kcal/mol (r=2.90 Å) to 0.1 kcal/mol (r=3.00 Å). Both levels of theories agree for r=3.05 Å with ∆E= -13.42 kcal/mol. The agreement between both levels is therefore better near the minimum region of CCSDR(3)/CBS, which lies close to 3 Å (see Fig. ).