The command CCSD performs a closed-shell coupled-cluster calculation. Using the CCSD(T) command, the perturbative contributions of connected triple excitations are also computed. For further information on triples corrections see under RCCSD.
Normally, no further input is needed if the CCSD card follows the corresponding HF-SCF. Otherwise, occupancies and orbitals can be specified as in the CI program. The only special input directives for this code are BRUECKNER and DIIS.
As well as the energy,
the diagnostic (T. J. Lee and P. R. Taylor, Int. J. Quant. Chem. S23
(1989) 23) is printed and stored in the variable T1DIAG for later analysis.