It is optionally possible to use the `SLAPAF` program written by Roland Lindh
for geometry optimizations. This is done by prepending the optimization method with 'SL'.
The following methods are supported:

`SLRF`- Use the rational function approximation;
`SLNR`- Use the Newton-Raphson method;
`SLC1`- Use the C1-DIIS method;
`SLC2`- Use the C2-DIIS method.

When using DIIS methods (`SLC1` or `SLC2`), the DIIS parameters are specified in the same way
as in standard molpro optimizer.

There are some differences when using the `SLAPAF` program:

- 1)
- It is not possible to use Z-matrix coordinates in the optimization.
- 2)
- Instead, one can explicitly define internal coordinates to be varied or fixed.
- 3)
- Additional constraints can be imposed on the converged geometry in a flexible way.

- 46.3.1 Defining constraints
- 46.3.2 Defining internal coordinates
- 46.3.3 Additional options for SLAPAF

molpro@molpro.net 2019-06-16