[Wien] incorrect band splitting when RLO added for a system with spatial inversion

[Martin Gmitra]

Dear Wien2k users,

I am facing a problem with symmetry preserved result when relativistic
local orbital (RLO) is added to the spin-orbit coupling calculations.

The system is bismuthene, a 2D layer of Bi atoms, in orthorombic
lattice WITH inversion.

Without RLO the bands are doubly degenerated, up to numerical
precision below 1 micro eV, (correct result).

By adding RLO for 5P_1/2 (found by autosearch to -8.08 Ry, close to
the -8.3 Ry from lstart) the bands split. For the top valence band it
can reach values of several meV (!), see plot in the attachment.
It stays degenerate at Gamma point while at the other time-reversal
invariant points (X, Y, and S point in the plot) it does not.

My question is:
How to improve precision?
Do you have any idea what could be reason for and provide possible
hint how to solve the problem?

Another (perhaps minor) point:
Autosearch finds RLO at -8.08 Ry while lstart finds for 5P_1/2 value
-8.3 Ry, what is behind the 0.2 Ry renormalization?

Note 1:
Calculations done by version 14.2, XC_PBESOL and default basis type
used, increasing Emax and Rmax do not improve results, the "ghost"
splitting stays there.

Note 2:
Wien2k version 16 gives similar results.
For intallation -- I had to patch the siteconfig script commenting line 148
    if("$test" != "/") goto iloop
otherwise it runs into the infinite iloop if the FFTWl_LIBS are not set up.


Best regards,
Martin Gmitra
Uni Regensburg
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