J. J. Ramsey wrote: > ----- Original Message ---- > > >> From: Stefano de Gironcoli <degironc at sissa.it> >> To: PWSCF Forum <pw_forum at pwscf.org> >> Sent: Thursday, August 13, 2009 11:59:14 AM >> Subject: Re: [Pw_forum] Trying to clarify the dipole correction (again!) >> >> Dear J.J. Ramsey >> >> at variance with what is defined in Bengtsson's paper the dipole >> potential is not discontinuous in QE but is defined by periodically >> alternating an increasing slope (associate to the "physical" electric >> field present in the cell) and a rapidly decreasing slope that should >> be located in a region of negligibly small charge density. This is done >> to avoid too sharp features in the calculation. >> > > In other words, the discontinuity in Bengtsson's paper, where the slope is > infinite, is replaced by a large but finite slope. > yes >> so if emaxpos = 0.45 and eopreg=0.1 the region where the correction >> is physically meaningful goes from -45% to +45% of the cell and the >> regression region (that should contains no charge density) occupies >> the central 10% of the cell. This is a good setting if you center your >> slab around the origin. >> > > I gather you mean the case where the slab is near the bottom of the unit cell. > or centered around the origin like in the the Al(001) surface of example03.. remember that we have periodic boundary conditions and the origin does not have any special meaning.
stefano