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.
If the CCSD is not converged, an error exit will occur if triples are requested. This can be avoided using the NOCHECK option:
In this case the (T) correction will be computed even if the CCSD did not converge. Note: NOCHECK has no effect in geometry optimizations or frequency calculations.
For further information on triples corrections see under RCCSD.