In GULP there is a command for applying stress on the cell;

stress and insrting the values

when I apply it on a crystal structure, in order to apply the stress along x, the structure seems to show a change in size for all axis, as opposed to what would be expected, a difference in the change in size for partiular axis of stress, thus it seems that stress is in fact considered as pressure rather than as it should be. May I have any reply in regards to this matter and how does GULP work out with such a command please?

Thanks

Reuben