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

[Ask Hjorth Larsen]

Dear Georg,

Am So., 13. Jan. 2019 um 17:57 Uhr schrieb Georg Kastlunger via
gpaw-users <gpaw-users at listserv.fysik.dtu.dk>:
>
> Dear Ask,
>
> thank you for your quick reply.
>
> I was able to converge the molecule now. The problem seemed to be the
> grid spacing. If I use a grid spacing below 0.18 the calculation does
> not converge.

Strange.  I did a test with libvdwxc, vacuum 6.5, and spacing 0.13 on
a desktop computer.  It converged in 19 iterations:

http://dcwww.camd.dtu.dk/~askhl/files/vdw-molecule-kastlunger.py
http://dcwww.camd.dtu.dk/~askhl/files/vdw-molecule-kastlunger.txt

(I again recommend switching to libvdwxc if at all possible, since the
old implementation is very inefficient)

Best regards
Ask

>
> Best wishes,
> Georg
>
>
> On 1/11/19 9:11 PM, Ask Hjorth Larsen via gpaw-users wrote:
> > 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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