[Pw_forum] How to change the electronic field direction

[Cao TF]

Dear PW users,
  I konw that with "tefied = .true. " we can apply an saw-like electronic potential to the system, with the direction and the shape are determined by edir, emaxpos, eopreg and eamp.  but I still do not know how to change the direction of the electronic field? For example, in the bilayer-graphene system,  with the vacuum in the Z direction and the bilayer-graphene in the position around 0.5, we can use "edir = 3", "emaxpos = 0.9", and "eopreg = 0.1 " to add an electronic field in the positive Z direction with amplitude determnined by the "eamp". So how to change such field direction, that is to add an electronic in the negative Z direction. I have confused with such question for a long time. So you suggestions are greated appreciated.    ------
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