Preliminary note

TURBOMOLE offers three programs for MP2 energy and gradient calculations. A "conventional" implementation [106], mpgrad, based on the calculation of four-center integrals (not further developed for several years), and two implementations which use the resolution-of-the-identity (RI) approximation: the implementation from 1997 [8] in rimp2 and a new implementation as part the CC2 program [10], ricc2.