Comment 12 for bug 1783785

Dear Nick,

I had read the manual and I was aware that I am not using appropriate
values of mesh cutoff, electronic temperature, etc, for a really
meaningful spin-orbit calculation. But I certainly would not expect to
obtain forces 3 orders of magnitude off just because of a low cutoff.
I checked that the cutoff is enough at least for the scalar relativistic
calculations.

Now I have progressively increased the cutoff up to near 500 Ry, and
lowered the electronic Temperature till 20 K. The forces are still about
109 eV/Ang. Something weird is going on here...files attached...

According to the literature, the spin-orbit effect on the gold dimer
should decrease the bond length by around 0.1 Ang, so I would expect to
obtain forces around 0.1-0.2 eV/Ang here.

Best wishes,

Andres

On Thu, 2 Aug 2018, Nick Papior wrote:

> You are using a very low meshcutoff. For SO you should use much higher
> values (please do a convergence test on this value).
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1783785
>
> Title:
> spin-polarized and spin-orbit calculations on a gold dimer crash
>
> Status in Siesta:
> New
>
> Bug description:
> Hi,
>
> I am using siesta-4.1-b3 version. I am calculating the gold dimer as a
> simple test of my pseudo and basis set. I have done all the main tests
> using a non-polarized calculation as Au_2 is obviously non-polarized.
> I found no problems at all. Then I wanted to see the effect of S-O
> coupling, but I first tried a spin-polarized calculation just as a
> sanity test. Both calculations (either spin-polarized or spin-orbit)
> proceed apparently well and the SCF convergence is reached. Just after
> that, when I guess the code prints out the final information (energy
> decomposition, dipole moment, etc) the code crashes, both in parallel
> and in serial (in serial I can read "Bus error"; in parallel not much
> information).
>
> I attach both the psf file with the pseudo and the fdf file below. I
> have checked that the mistake is only in the "Spin" order. If you set
> "Spin non-polarized" it works. If you just change this to "Spin
> polarized" it crashes.
>
> Any help will be appreciated. I'm not sure of this is a bug of a
> compiling problem, but the code compiled without any problem. And the
> spin-unpolarized calculation gives almost exactly the same result as
> 4.0.2 version, so it seems OK.
>
> Thanks in advance
>
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