Prerequisites

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. an auxiliary basis defined in the data group $cbas
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, and $rir12 have to be set (see below and Section 15.2.13).

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 and $rir12.

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 (C₁, C_s, C₂, C_i, C_2h, C_2v, D₂, D_2h). The F12 correction can only be calculated in the C₁ point group.