BCCD performs a Brueckner coupled-cluster calculation and computes Brueckner orbitals. With these orbitals, the amplitudes of the singles vanish at convergence. Using the BCCD(T) command, the contributions of connected triples are also computed by perturbation theory. Normally, no further input is needed if the BCCD card follows the corresponding HF-SCF. Otherwise, occupancies and orbitals can be specified as in the CI program. For modifying DIIS or BRUECKNER parameters, see CCSD.