I've tried to find proper answers for it but cannot find one.
1. So the question is that is it possible or reliable to apply external electric field on 3D system in VASP?
There are some works on 2D system with external electric field like graphene, but it seems like there's nothing regarding 3D system.
I found that EFIELD, LDIPOL, IDIPOL, EFIELD_PEAD are key tags to apply external electric field.
However, in the web ( https://www.vasp.at/wiki/index.php/EFIELD ) it states only about slab or molecule model.
Also, EFIELD_PEAD looks like it has no effect on geometry
( https://www.vasp.at/forum/viewtopic.php?t=17390&p=18296 ), only affects to electronic structure.
2. The second question here is that do the other three tags(EFIELD, LDIPOL, IDIPOL) also give changes to electronic structure only or geometrical change also?
Thank you
Dear Honghui Kim
It is physically meaningless to apply electric field in a 3D bulk system. Electric filed is by definition a gradient of potential, meaning that It starts from a particular point and ends at another point. In programs like VASP or QE, to model this behavior a saw-tooth like potential is created with two opposite slopes. In the first region the slope of potential is positive starting from the point you define and reaching its maximum at the end point that you again define. From the latter point a new potential with opposite slope is created that linearly reaches zero again at the starting point. This allows to maintain the translational symmetry of the whole Bloch space. Now within the positive slope range you can assume a dielectric slab, thin film or monolayer is placed and vacuum will fill the negative-slope one. Since vacuum contains no charge, then the negative slope potential will have no impact on your calculations. So everything will work just fine.
For a truly 3D system however, you can't separate the positive-slope region from the negative one, as they separately affect parts of your system. Using Poisson equation, it is easy to show the total effect of such an electric field will be Zero! Thus, it makes no sense to do such a thing for bulk systems. Hope this information helps!
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