[Pw_forum] CuBTC open metal organic frameworks CONVERGENCE

[Nicola Marzari]

On 23/01/2017 12:37, Francesco Pelizza wrote:
> Hello dear community,
>
>
> Here in strathclyde some colleagues are using QE to relax and than study
> some MOF's.
>
> The problem starts from the beginning, no convergence in the first SCF
> cycle before a fixed cell relaxation.


One more, if unrelated - the conv_thr you use is extremely tight
(this is not related to your original problem, but it only means that
once you have found a robus recipe for convergence, it might be tough
to get to such a tight tolerance). This is because, as mentioned in

http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html
---
Convergence threshold for selfconsistency:
    estimated energy error < conv_thr
(note that conv_thr is extensive, like the total energy).
---

it means that if say 1e-6 is a good conv_thr value for a system with a 
few atoms,
if a system is 10 times larger conv_thr should typically be 10 times larger
as well (i.e. 1e-5)

			nicola



>
>
> We took care of spin polarized calculation, switched to non polarized
> calculation and many other things, WFC from 50 to 80 Ry and RHO cutoffs
> 10 times the WFC, with gamma sampling and 3 x 3 x 3.
>
> Also checked the smearing, degauss values, nothing seemed to make the
> convergence better.
>
> Here you can find some input files and output files.
>
>
> We used ultrasoft pseudopotentials applying PBE and then vdW-DF
> functionals.
>
>
> No success at all.
>
>
> Please some of you have better experience of us in these systems to tell
> us what we do wrong?
>
>
> BW
>
> Francesco Pelizza and Chris Campbell
>
>
> Strathclyde University
>
>
>
>
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-- 
----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, EPFL
http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project