Calculations with the ricc2 module require (almost) the same prerequisites as RI-MP2 calculations:

- 1.
- a converged SCF calculation with the one-electron density convergence threshold set to $denconv 1.d-5 or less
- 2.
- if non-standard basis sets used: an auxiliary basis defined in the data group $cbas (for standard basis sets, where a corresponding auxiliary basis set is found in the basis set library, the program will automatically use this if $cbas is not set)
- 3.
- if orbitals should be excluded from the correlation treatment (and excitation processes) 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.
- depending on the type of calculations that should be carried out, additionally the data groups $ricc2, $excitations, $response, $laplace, $rir12 and $lcg have to be set (see below and Section 21.2.17).

For calculations with the ricc2 program it is recommended to use the cc2 submenu of the
define program to set the data groups $denconv, $freeze, $cbas, $maxcor. MP2-F12
calculations require in addition the data groups $rir12, $cabs, $jkbas and $lcg. The exponent of
the Slater function in the interelectronic distance r_{12}, which appears in the geminals used
MP2-F12 is defined in the data group $lcg and should be adapted to the one-electron basis set
which is used.

Note, that the implementation of non-Abelian point groups in ricc2 is limited to the electronic
ground state (but comprises all of the RI-MP2 functionality included in ricc2). In the present
version ricc2 can for excited states only deal with real Abelian point groups (C_{1}, C_{s}, C_{2},
C_{i}, C_{2h}, C_{2v}, D_{2}, D_{2h}). The F12 correction can only be calculated in the C_{1} point
group.