Adding an external potential to a calculation?

[jms]

Hi, I would like to perform a calculation which includes some external potential. I don't want to go into the details of why or exactly what the potential is (suffice it to say it is a step-like potential), but my question for the community is how I could implement such a modification?

I am assuming I will have to modify the source code to some extent and compile a custom version, so I was hoping someone might be able to help me get started.

Some specific questions that would be very useful to answer would be, which files in the vasp source code would need to be edited, which lines within those files are important, and if there is any limitations to what kind of function I can add as an external potential. Additionally, if anyone knows of any resources describing a similar kind of modification, that would be extremely helpful.

Thanks!

[jms]

So I stumbled on the subroutine EXTERNAL_POT in pot.F. Seems like what I need - but I'm a little unclear about how the data structures CVTOT (declared as an RGRID type within this subroutine) and GRIDC (grid_3d) work and what exactly the subroutine is doing...

Does anyone have any experience editing this subroutine and could maybe explain what they've learned?

[askhetan]

let me guess - you're trying to model an electrode surface at a given potential (or an electrochemical reaction at a given potential). if yes then you might want to look at the double reference method as devised by taylor and neurock... where they describe a rather step wise method to specify a surface potential by adding excess electrons. if not, i really do not think what you're aiming at can be done by modifying some subroutines or scripts...... because this is a very sought after problem and if it was possible to specify surface potential, a lot of electrochemical studies would become very meaningful. in case you're successful, please do let us know. thanks!!