(
2) but has for small and medium-sized systems a larger
prefactor than ricc2.
TURBOMOLE offers three programs for MP2 energy and gradient calculations. A "conventional"
implementation [129], mpgrad, based on the calculation of four-center integrals, an implementation
which uses the resolution-of-the-identity (RI) approximation [130] as part the RI-CC2
program [8], ricc2, and an implementation which is meant for very large (> 100 atoms and
> 3000 basis functions) single point MP2 energy calculations. The latter program uses in addition
to a local RI also a hybrid OSV-PNO approximation to reduce the scaling of the computational
costs with the system size to ≈(2) but has for small and medium-sized systems a larger
prefactor than ricc2.