Comment 13 for bug 1783785

Dear Nick,

I have been trying a few other things, and I have found something.

Before trying the S-O calculations, I first performed scalar relativistic
calculations, on which I optimized the basis set and tested the pseudo.
The basis is quite big as I wanted to reproduce well-converged plane wave
results as a benchmark. In the process, I generated several basis sets of
increasing complexity.

Now I decided to perform S-O calculations on each of those increasingly
more complex basis sets, and I have found that most of these calculations
produce reasonable results. As an example I attach the biggest basis that
produces physically sensible results (see the forces of about 0.1
eV/Ang.).

The only difference between this basis and the most complete one is that I
switched from DZ to TZ also in the "d" channel. Just by adding a third
zeta to the "d" basis functions changes the forces from 0.1 to 100 ev/Ang
and the spin-orbit energy (Eso in the code) from about -0.5 to about -100
eV. Meanwhile, moving from DZ to TZ in the scalar relativistic
calculations just lowered the energy by about 0.01 eV.

In practice, I can just dispense with the TZ "d" basis and it seems it
works. But it is an issue for the developers to understand what exactly is
going on here, because increasing the basis size should be possible also
in S-O calculations.

I am not sure if the error is just an issue of my compiler. I understand
that you optimize SIESTA based on the most modern compiler versions. It
would be nice to know if you also get unphysical results in your machines.

Well, at least this is an advance! Thanks for your help again!

Best wishes,

Andres