[Pw_forum] converging V_xc in the vacuum

Janos Daru janos.daru at gmail.com
Fri Feb 16 17:30:55 CET 2018

Dear experts,

I would like to print out plane averaged exchange-correlation potential for
a PBE Cu(111) slab along its normal vector (z-direction).
To this end I have printed out plot_num:

1  = total potential V_bare + V_H + V_xc
11 = the V_bare + V_H potential

and subtracted the second from the first and averaged it.
However, unlike in JCTC 2009,5,881-886 (figure 3.) or in Nano Lett.
2015,2448-2455 (figure 3.) V_xc does not converge to zero in the vacuum
region (it has an approximate value of  -0.015 Hartree).

The SI from the second paper authors explains that:
"we note that it is well-known that in the vacuum the exchange-correlation
(xc) part converges much more slowly than the electrostatic part of the
total potential. Therefore, when computing the local potential of bare
graphite(0001) and Au(111), we employed more strict settings in the
band-structure calculations. Specifically, we increased the number of
FFT-grid points and enhanced the representation of the charge density,
potential and augmentation charges. Furthermore, we have employed an
additional support grid for the augmentation charges, which further
increases the accuracy of calculated quantities."

So I tried to tighten ecutrho, the realspace grid, the convergence
criteria, I have increased the vacuum, number of Cu layers etc. but V_xc
does not converge to zero in the vacuum. Could some of the experts explain
to me if it is due to a wrong setup, or eg. due to a different reference

I have attached the full input, and V_xc plot. I have used QE 5.2.0 for my

Thank you for the answer in anticipation,

Janos Daru
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20180216/3d47d172/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: input
Type: application/octet-stream
Size: 1898 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20180216/3d47d172/attachment.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Vxc.pdf
Type: application/pdf
Size: 37416 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20180216/3d47d172/attachment.pdf>

More information about the users mailing list