A general comment about convergence, as there have been a few recent

Convergence is similar to paddling a canoe down a river from the mountains
to the sea. Sometimes the water is rushing by and you (the mixer) have to
try and avoid the rocks (ghost bands); sometimes you go over a waterfall
and the problem changes (electronic phase transition); sometimes you are on
a meandering river and do not seem to be making progress.

Check-mixing is designed to give some idea about what is going on, as a
simple grep on :DIS, for instance, does not reveal enough.

Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi

On Tue, Nov 26, 2019, 07:21 Luigi Maduro - TNW <l.a.mad...@tudelft.nl>

> Hello there WIEN2k users,
> I am having a convergence problem with a supercell calculation of a slab
> of MoS2 including Spin-Orbit Coupling (SOC). The supercell is made by
> cutting in the plane of MoS2 which leads to either only edge Mo atoms or
> edge S atoms. A vacuum parallel to the edges is introduced (about 18
> angstroms) that separates the repeating images. Converged SCF calculations
> without SOC were found with this type of geometry for various widths. These
> converged SCF calculations were then used as input for an SCF calculation
> with SOC for the different widths. However, when including SOC only the
> smallest width gave a converged SCF calculation, albeit after doubling the
> amount of k-points and increasing nbands(more than twice what was
> originally suggested when running init_so). The larger widths do not result
> in a converged SCF calculation, even after substantially increasing nbands.
> Is the solution to just keep on increasing the amount of k-points until I
> do get converged SCF calculations or is the inclusion of the vacuum giving
> problems for lapwso?
> As a side not, I have a general question on how to relate Emax and nbands
> in case.in1. Up until recently I have been using SCALAPACK in WIEN2k and
> now I have switched to using ELPA. In the case of MoS2, a system with large
> spin-orbit coupling, the userguide recommends to increase the value of Emax
> to up to 10 Ry for large SOC systems when running the init_so script. If
> one is using ELPA then nbands should be increased. In the case of ELPA
> should nbands be increased to twice the amount given in case.in1 when
> initially running init_so?
> PhD candidate
> Kavli Institute of Nanoscience
> Department of Quantum Nanoscience
> Faculty of Applied Sciences
> Delft University of Technology
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