Prerequisites

CCSD and CCSD(T) calculations with the ricc2 module require the same prerequisites as RI-CC2 calculations,

1. a converged SCF calculation with the one-electron density threshold set to $denconv 1.d-5 or less
2. an auxiliary basis defined in the data group $cbas
3. if orbitals should be excluded from the correlation treatment the data group $freeze has to be set
4. the maximum core memory which the program is allowed to allocate should be defined in the data group $maxcor; the recommended value is 66-75% of the available (physical) core memory.
5. the data group $ricc2 with a specification of the coupled-cluster model

Calculations with the CCSD(F12) methods require in addition:

• the data group $rir12 with the definition of the standard approximations for the explicitly-correlated contributions (see Sec. 8.5 for details)
• the data group $lcg, which define the correlation function (here it is in particular important to choose for F12 calculations the exponent; recommended values are 0.9 for cc-pVDZ-F12, 1.0 for cc-pVTZ-F12 and 1.1 for cc-pVQZ-F12 basis sets)
• a complementary auxiliary (CABS) basis set

Furthermore it is recommeded to select in addition an auxiliary JK basis set for the evaluation of the Fock matrix elements. (The rijk menu of define can be used for this.)