On 06/30/2018 04:28 PM, Roberto Gomes de Aguiar Veiga wrote:
However, when I try to perform calculations for the
corresponding surfaces, they do not converge. I've been using
mixing_mode='local-TF' and descreasing mixing_beta to values as low as
0.05 for the surface calculations, with no success. Can any of you with
experience in this kind of simulation (DFT+U and surfaces) share what
you usually do to have converged calculations?
Hello Roberto,
DFT+U and surface is a bit tricky, because in principle there is not
guarantee that the value of U used for the bulk is transferable to the
surface atoms. We all do it, but it is not justified.
I also find it very difficult to converge DFT+U for surfaces. One
approach I have used is to defined different species for atoms of the
uppermost layers and for deeper atoms, to be able to define different
starting magnetization. Also, I do not refrain to increase electrons max
steps to 1000 or more, sometimes it just take that long to converge!
Finally, a trick which I have used is to use starting_ns_eigenvalue and
mixing_fixed_ns to some large value (e.g. 1000) to get a first converged
charge density with ns eigenvalues kept fixed, that do a
restart="from_scratch" with startingpot="file" (this time without
mixing_fixed_ns, or setting it to a small value).
If you notice that the ns eigenvalues printed in output are less
symmetric than the initial magnetization, it may be a good idea to split
the definition of the +U species until they do, this way you can define
different initial ns for them.
hth, it is a lot of cooking
--
Lorenzo Paulatto - Paris
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