Improved general scaling factors and systematic tests of the SAC method for estimating correlation energies of molecules

We test the scaling-all-correlation (SAC) method with Mّller-Plesset second-order perturbation theory (MP2-SAC), the coupled-cluster approximation with double substitutions (CCD-SAC), and quadratic configuration interaction with singles and doubles (QCISD-SAC) with various choices of basis set. The CCD-SAC and QCISD-SAC methods lead to good accuracy with an average scaling factor and are recommended when affordable, and for practical work it is useful to note that the MP2-SAC method with a parabolic fit to the scaling factor outperforms the more expensive CCD-SAC and QCISD-SAC methods with the same basis and averaged scaling factors.