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`- Ignore convergence checks.
`DIRECT`- Do calculation integral direct.
`NOSING`- Do not include singly external configurations.
`MAXIT=`*value*- Maximum number of iterations.
`SHIFTS=`*value*- Denominator shift for update of singles.
`SHIFTP=`*value*- Denominator shift for update of doubles.
`THRDEN=`*value*- Convergence threshold for the energy.
`THRVAR=`*value*- Convergence threshold for CC amplitudes. This applies to the square sum of the changes of the amplitudes.
`SAVE=`*record*- Save CCSD wavefunction to this record
`START=`*record*- Restart CCSD wavefunction from a previously written record

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 diagnostic (T. J. Lee and P. R. Taylor, Int. J. Quant. Chem. S23 (1989) 199) and the 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.

For geometry optimization and computing first-order properties see section 24.11.

- 24.1 Coupled-cluster, CCSD
- 24.2 Quadratic configuration interaction, QCI
- 24.3 Brueckner coupled-cluster calculations, BCCD
- 24.4 Singles-doubles configuration interaction, CISD
- 24.5 Quasi-variational coupled cluster, QVCCD
- 24.6 Distinguishable cluster, DCD
- 24.7 The
`DIIS`directive - 24.8 Saving the wavefunction
- 24.9 Starting wavefunction
- 24.10 Examples
- 24.11 Expectation values
- 24.12 Saving the density matrix
- 24.13 Natural orbitals
- 24.14 Dual basis set calculations

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