### Synopsis

`
[-]( arp | rap | repar )` 1|2|3|4|5

### Description

This keyword allows to specify which set of Repulsion Atomic
Parameters has to be used for calculation of atom-atom exchange-repulsion
interaction energies.

The following sets are available:

- Original Spackman's Atomic Parameters, SAP's (Spackman, 1986)
- Scaled SAP's to fit Ziegler-Rauk ADF-BLYP/TZP repulsion energies.
- Least-squares refined AP's, which fit Ziegler-Rauk ADF-BLYP/TZP repulsion
energies. Available for H, C, N, O and S. For the remaining atoms, option 2
is adopted.
- Scaled SAP's to fit Kitaura-Morokuma GAMESS-HF/6-31G(d) repulsion
energies.
- Least-squares refined AP's, which fit Kitaura-Morokuma GAMESS-HF/6-31G(d)
repulsion energies. Available for H, C, N and O. For atom S the value of
option 3 is adopted. For the remaining atoms, option 4 is adopted.

Option 5 is the default.

### Remarks

Calculation of exchange-repulsion interaction energies,
using a Born-Mayer potential.

### Related Keywords

### References

"Atom-atom potentials via electron gas theory"

Mark A. Spackman

*J. Chem. Phys.* **1986**, *85*, 6579-6586.