[gpaw-users] Trouble converging simple molecule with BEEF-vdW

[Ask Hjorth Larsen]

Dear Georg,

Am Sa., 12. Jan. 2019 um 02:00 Uhr schrieb Georg Kastlunger via
gpaw-users <gpaw-users at listserv.fysik.dtu.dk>:
>
> Dear GPAW community,
>
> I am currently having some trouble converging a calculation of a simple
> molecule (4-mercaptobenzoic acid) applying the BEEF-vdW XC-functional.
>
> Relaxing the same structure with RPBE did not create any problems
> before. Also, when adsorbing the molecule to a metal slab the
> calculation converges like a charm.
>
> I have attached the structure and a minimal script. As you can see, I
> have already played around with some parameters for improving
> convergence. Unfortunately, nothing helped.
>
> Did anyone experience the same issue before and knows about some tricks
> to converge this system?

I ran it using the libvdwxc backend and it converged in 16 iterations,
although I changed gpts/vacuum so it would run on an old laptop.

calc = GPAW(h=0.2,
            xc={'name': 'BEEF-vdW', 'backend': 'libvdwxc'},
            txt='out.txt',
            eigensolver = Davidson(3),
            )
atoms.set_calculator(calc)
atoms.center(vacuum=4.0)

The libvdwxc backend requires installing (drumroll) libvdwxc.  It is
much faster, uses less memory, and is scalable (the old implementation
scales to 20 cores max, and some things are not parallel).  However it
uses a different parametrization of the kernel and does not include
the 'soft correction', which means the values will differ slightly.

As for the old (slow) implementation, I see now that it also converged
after 16 iterations with the same parameters as above.  But I am using
GPAW master (i.e. 1.5.0 basically).

Best regards
Ask

>
>
> Thank you in advance,
>
> Georg
>
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