Prepare a normal RI-CC2 calculation. Note that you have to start from a previous PE-SCF run. The information for the polarizable embedding is the same as for the SCF case and contained in the data group `$point_charges pe`.

There are some additional options to control the PERI-CC2 calculations. As noted in the theory section, one has to solve a coupled set of equations for the ground state. This is done iteratively until convergence is achieved which is controlled with an outer loop as well as some micro iterations for the multiplier and amplitude solver. Normally, the default options should be fine but they can be changed by modifying the `control` file:

Options in `$ricc2` block in file `control`:

$ricc2 pe_maxiter <int> pe_maxt0iter <int> pe_maxl0iter <int>

`pe_maxiter`- : maximum of macro iterations (default: 50)
`pe_maxt0iter`- : maximum of micro iterations in T0-solver (default: 4)
`pe_maxl0iter`- : maximum of micro iterations in L0-solver (default: 4)

There are several limitations for the use of PERI-CC2:

- only ground state energies, excitation energies and transition moments are supported (no other properties or gradients and so on)
- no other wave function model than CC2 is supported
- no use of symmetry
- no MPI parallelization is available (but SMP binaries work)
- open-shell systems are not covered