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

[Georg Kastlunger]

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.

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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