MOLPRO

24 THE CLOSED SHELL CCSD PROGRAM 182
24 THE CLOSED SHELL CCSD PROGRAM
Bibliography:
C. Hampel, K. Peterson, and H.-J. Werner, Chem. Phys. Lett. 190, 1 (1992)
All publications resulting from use of this program must acknowledge the above.
The CCSD program is called by the CISD, CCSD, BCCD, or QCI directives. CID or CCD can
be done as special cases using the NOSINGL directive. The code also allows to calculate Brueckner
orbitals (QCI and CCSD are identical in this case). Normally, no further input is needed if
the CCSD card follows the corresponding HF-SCF. Optional ORBITAL, OCC, CLOSED, CORE,
SAVE, START, PRINT options work as described for the MRCI program in section 20. The
only special input directives for this code are BRUECKNER and DIIS, as described below.
The following options may be specified on the command line:
NOCHECK
DIRECT
NOSING
MAXIT=value
SHIFTS=value
SHIFTP=value
THRDEN=value
THRVAR=value
Ignore convergence checks.
Do calculation integral direct.
Do not include singly external configurations.
Maximum number of iterations.
Denominator shift for update of singles.
Denominator shift for update of doubles.
Convergence threshold for the energy.
Convergence threshold for CC amplitudes. This applies to the square
sum of the changes of the amplitudes.
The convergence thresholds can also be modified using
THRESH,ENERGY=thrden,COEFF=thrvar
Convergence is reached if the energy change is smaller than thrden (default 1.d-6) and the square
sum of the amplitude changes is smaller than thrvar (default (1.d-10). The THRESH card must
follow the command for the method (e.g., CCSD) and then overwrites the corresponding global
options (see GTHRESH, sec. 6.11).
The computed energies are stored in variables as explained in section 8.8. As well as the energy,
the T 1 diagnostic (T. J. Lee and P. R. Taylor, Int. J. Quant. Chem. S23 (1989) 199) and the
D 1 diagnostic (C. L. Janssen and I. M. B. Nielsen, Chem. Phys. Lett. 290 (1998), 423, and
T. J. Lee. Chem. Phys. Lett. 372 (2003), 362) are printed and stored for later analysis in the
variables T1DIAG and D1DIAG, respectively.
24.1 Coupled-cluster, CCSD
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:
CCSD(T),NOCHECK
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.