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#

Counterpoise-Corrections using the JOBBSSE Script

The shell script `jobbsse` controls and executes the automatic calculation
of the counterpoise correction as it has been formulated by
Boys and Bernadi (S. F. Boys and
F. Bernardi, Mol. Phys., **19,** 553 (1970)) to estimate the
Basis Set Superposition Error (BSSE).
For a dimer, the cp-correction takes the form for the monomers A and B:
*E*^{CP}_{AB} = *E*_{AB} - (*E*_{A(B)} - *E*_{A}) - (*E*_{B(A)} - *E*_{B})

Where parentheses denote ghost basis sets without electrons or nuclear charges.
For a timer `jobbsse` used by default the conventional so-called
site-site functional counterpoise corrections:
*E*^{CP}_{ABC} = *E*_{ABC} - (*E*_{A(BC)} - *E*_{A}) - (*E*_{B(AC)} - *E*_{B}) - (*E*_{C(AB)} - *E*_{C}) .

`jobbsse` works similar as the `jobex` script: it cycles through the
SCF/DFT and, if needed, gradient and force relaxation programs and
stops if either the maximum number of cycles is reached or
the convergence criteria (change in the total energy, maximum norm of
the gradient) are fulfilled. It does either only energy calculations
or a full geometry optimization including up to three fragments.
By default, the executable programs are
taken from the load modules library within the `TURBOMOLE` directory.
Note that you need to set up the fragments (and possibly their symmetries
using `define` in the geometry menu beforehand.
The general structure of a `jobbsse` calculation is as follows:

`bsseenergy` is invoked to generate input files for `define`, which
is then used to prepare the control files (including occupation numbers,
initial guess MOs, etc.) for the different ``ghost`` and monomer
calculations and shell scripts with commands for calculations on these
fragments.
`jobbsse` cycles over the supermolecular complex and the fragments
and computes the energies and, if requested, gradients for them.
Then the counterpoise-corrected results are evaluated and written
to the standard data groups ($energy and $grad).
- For geometry optimizations one of the structure relaxation codes
(
`statpt` or `relax`) is invoked to update the coordinates and check
for convergence. If the structure optimization is not converged
`jobbsse` continues with the previous step.

Note, that counterpoise-corrected calculations with `jobbsse` are NOT
as black-box as ordinary geometry optimizations with `jobex`.
The input generated for the fragments are based on the default
occupation numbers obtained from the EHT guess, default assignments
for the frozen orbitals, memory, etc.
Since this might be different from what is needed (or even fail),
it is recommended to let `jobbsse` stop after
the initial setup step using the flag `-setup` and to check
carefully the assigned basis sets, occupations number and subsystem
symmetries.
In particular, for MP2 or CC2 calculations with molecules
containing not only the atoms H-Ar also the number of frozen orbitals
should be checked, and if neccessary corrected.

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