[QE-users] DFPT of thin metal layer: convergence has not been achieved

Stefano Baroni baroni at sissa.it
Tue Nov 6 14:41:07 CET 2018

Dear Chris,

I do not know what the origin of your problem may be. What I can say is that it is probably not a good idea to run such a relatively large computation just to evaluate the vibrational properties of a thin metal layer. A smarter approach would probably be to compute interatomic force constants using a thinner slab (the range of the force constants is likely 2-3 bond lengths in Cu), and than to use the ab initio force constant to build a model for a slab of any thickness … By the way the size of the vacuum region is likely also an overkill …


> On 6 Nov 2018, at 14:31, Christoph Wolf <wolf.christoph at qns.science> wrote:
> Dear all,
> I am trying to calculate the phonon spectrum for a series of thin metal layer. However there seem to be a few "pathological" cases such as Cu(111) where, no matter what, I cannot achieve convergence during the ph.x calculation.
> I have tried, to no avail, change mixing parameter, k point sampling, ecutrho, ecutwfc, smearing type, occupation type, ...
> If someone has a hint on how to tackle this I would be entirely grateful. I know it can be done as there are a few works out there focusing on thin metal film phonons but non of them has additional information.
> The general setup is 11 layers of metal padded by 20A of vacuum. I generated the layers using "thermo_pw" and I manually and meticulously checked bond lengths and residual forces on the atoms after relaxation (<1e-6). 
> Any help is very welcome!
> Thanks in advance and with best regards,
> Chris 
> -- 
> Postdoctoral Researcher
> Center for Quantum Nanoscience, Institute for Basic Science
> Ewha Womans University, Seoul, South Korea
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Stefano Baroni - Trieste —  http://stefano.baroni.me <http://stefano.baroni.me/> 

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