[Pw_forum] Trying to clarify the dipole correction (again!)

[J. J. Ramsey]

In the reference on the dipole correction used in QE, L. Bengtsson, PRB 59, 12301 (1999), the dipole potential is given as

V_dip(z) = 4*pi*m*(z/z_m - 0.5), 0 < z < z_m

where z_m is the height of the box, and there is a discontinuity in the potential at z = 0,z_m. I'm not sure how this fits into the QE documentation on the dipole correction. Is V_dip in QE supposed to be something like this?:

V_dip(z) = 4*pi*m*[z/z_m - (emaxpos + eopreg -1)], emaxpos + eopreg -1 < z/z_m < emaxpos;
         = something with a steep but finite slope, otherwise

My guess is probably wrong, but the explanations in the documentation of the roles of emaxpos and eopreg appear to be tied to the case where eamp  is nonzero. I'm not sure if the documentation for the dipfield variable is supposed to indicate that the actual slope of the potential is supposed to be eamp + 4*pi*m/z_m.

University of Akron
Civil Engineering (!) Dept.