Gaussian 03 Online Manual
Last update: 4 October 2006


These method keywords request a coupled cluster [67,422] calculations, using double substitutions from the Hartree-Fock determinant for CCD [67], or both single and double substitutions for CCSD [68,69,70,71]. CC and QCID are synonyms for CCD.

All frozen core options are available with CCD and CCSD.

Include triple excitations non-iteratively [72] (CCSD only). CCSD-T is a synonym for CCSD(T).

Used with the T option to request inclusion of triple excitations for both the complete MP4 and to form CCSD(T).

Computes the T1 diagnostic of T. J. Lee and coworkers [423](CCSD only).

Sets the convergence calculations to 10-N on the energy and 10-(N+2) on the wavefunction. The default is N=7 for single points and N=8 for gradients.

Specifies the maximum number of cycles for CCSD calculations.

Analytic energies and gradients for CCD and CCSD, numerical gradients for CCSD(T), and numerical frequencies for all methods.

MP4, Transformation, QCISD

The Coupled Cluster energy appears in the output as follows (following the final correlation iteration):

DE(CORR)=  -.54979226D-01         E(CORR)=   -.75019641794D+02 
CCSD(T)=  -.75019717665D+02

The CCSD energy is labeled E(CORR), and the energy including the non-iterative triples contribution is given in the final line.