[gpaw-users] Boundary conditions for poisson solver different for grid and pw mode?

[Chengjun Jin]

Dear Filip,

With FD mode and your structure, I got  the slope of zero at the z-boundary. Plots are attached.

Regards,
Chengjun


 
________________________________________
From: gpaw-users-bounces at listserv.fysik.dtu.dk [gpaw-users-bounces at listserv.fysik.dtu.dk] on behalf of Filip Anselm Rasmussen [fras at fysik.dtu.dk]
Sent: Friday, November 28, 2014 11:31 AM
To: gpaw-users at listserv.fysik.dtu.dk
Subject: [gpaw-users] Boundary conditions for poisson solver different for grid and pw mode?

Dear GPAW'ers

I am calculating the vacuum level of graphene and noticed that it varied
with ~0.3 eV depending on whether I use FD or PW mode. The calculations
seem to be very well comverged, so I plotted the in-plane averaged
effective potential along the z-direction (see attached figures) and
noted that even though I use periodic boundary conditions (even in the
z-direction where I have only one k-point), the slope of the FD
effective potential at the boundaries is not zero as I expected. In PW
mode the slope seems to be zero.

So my question is: Does FD mode use non-periodic boundary conditions if
there is only one k-point along some axis - even though you have
pbc=True for your Atoms object?

Input scripts have been attached. I calculate the effective potential
along z like this:

Veff_z = np.mean(np.mean(calc.get_effective_potential(), axis=0), axis=0)


Thanks,
Filip Rasmussen
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