[gpaw-users] Dipole correction with implicit solvent

[Georg Kastlunger]

Hi Ask,

thank you for the fast reply, where you confirm my understanding of the 
routine.

I suppose the subtraction and solvation of the poisson 
equation(accounting for the FDPoissonsolver boundary conditions), and 
addition (giving two distinct vacuum levels) are performed via these two 
lines:

iters = self.poissonsolver.solve(vHt_g, rhot_g + drhot_g, **kwargs)
vHt_g += dvHt_g

However, I do currently not understand why dvHt_g  is subtracted from 
the electrostatic potential beforehand. Is it done in order to create a 
good starting guess for the poisson solver? What puzzles me is that, 
although dvHt_g is constant at the outer parts of the unit cell the 
resulting potential is sometimes not flat near the boundary, when I 
scale it and keep the correcting charge density drhot_g untouched.

When you have more time, I would be happy to here your expertise on 
that. However, don't feel pushed, since I was just wondering how this 
can happen.

Best wishes,
Georg

On 02/04/2017 09:54 AM, Ask Hjorth Larsen wrote:
> Hi! Since the equation is linear, the correction works by adding 
> something to remove the dipole, then solving, then re-add the 
> necessary compensation to the solution. I am a bit busy but can 
> provide more details later.
>
> Best regards
> Ask
>
>
> El 4 feb. 2017 15:06, "Georg Kastlunger via gpaw-users" 
> <gpaw-users at listserv.fysik.dtu.dk 
> <mailto:gpaw-users at listserv.fysik.dtu.dk>> escribió:
>
>
>     Dear gpaw community,
>
>     I am currently working on a dipole correction combined with the
>     provided
>     implicit solvent model in GPAW. This has proven to be quite a
>     challenge
>     in terms of electrostatics and I am afraid I am not able to
>     capture the
>     physics correctly, unless I can understand the routine for the dipole
>     correction completely.
>
>     Therefore, I was wondering if there is any literature reference which
>     explains the reasoning behind the dipole correction in fd mode.
>
>     One question upfront:  Why is the potential representing the dipole
>     contribution (dvHt_g) subtracted before the poisson equation is
>     solved?
>     Does that mean that the starting guess for the potential is
>     changed?  I
>     noticed that if I change dvHt_g it changes the slope at the outer
>     parts
>     of the resulting electrostatic potential, even though dvHt_g is always
>     constant in those regions.
>
>     Best wishes,
>     Georg
>
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