I am trying to run a simple CASTEP optimization of a slab of a metallic material with dipole correction in order to get the workfunction value. To do so, i added to the .param file the following parameters:

dipole_correction : selfconsistent

dipole_dir : z

The optimization then finishes succesfully, however, when I check the output, I find the following warning:

WARNING: Ewald dipole correction: require c along z

- hence turning correction OFF

For each SCF cycle, which probably means the correction is not being applied.

I also tried changing the metals_method to edft from dm, with no avail, the warning keeps appearing.

How can I correctly apply this correction? For what I understand, it is necessary for accurate calculation of the workfunction. Is there any other specific parameter that needs to be accounted in order to apply dipole correction?

Many thanks for your answers.