The `ALTER` directive of the `SURF` program allows to provide error correction schemes for individual single point calculations.
For example, in case that the Hartree Fock calculation for a certain grid point did not converge and the `ORBITAL` directive in
the subsequent electron correlation calculation uses the `IGNORE_ERROR` option, an alternative calculation scheme can be
provided, e.g. MCSCF in contrast to RHF. In the case of *multi level* calculations the
`ALT2D` and `ALT3D` options can be set according to the `START2D` and `START3D` options.
Note that the energy variable has to be the same in the original method and the alternative.

`ALT1D`=*label*- Alternative procedure to calculate the 1D single points.
`ALT2D`=*label*- Alternative procedure to calculate the 2D single points.
`ALT3D`=*label*- Alternative procedure to calculate the 3D single points.

Note that DFT calculations often still converge when RHF calculations already fail to do so.

molpro@molpro.net 2019-05-25