[DFTB-Plus-User] Bulk/slab Fe optimization problems using pbc-0-3 or trans3d-0-1 parameters

[Branislav Milovanović]

Dear all,
>>>You could constrain the cell as being hexagonal (either Isotropic or FixAngles in the geometry optimiser),>>>also did you use hexagonal appropriate k-points (Monkhorst-Pack grid shifts are different in this case)?
Yes I tried this but there is no significant improvement.
> I recompiled program and now I get reasonable structures.
>>>That's a little bit worrisome, the results should not depend on the
>>>compilation on the program... If in doubt, try the official binaries via
>>>Conda, they should be OK.
Don't know what went wrong. Maybe there was some problem with the compiler, I'm not sure...
>Actually, I'd advise to set both, ShellResolvedScc as well as
>ShellResolvedSpin to "Yes".
I get a parser error when I try this. In most recent manual on page 41 it says:,,When ShellResolvedSCC = No, an extra keyword in this block controls whether the spin constants
are resolved by shell or are identical for all shells: ShellResolvedSpin, defaulting to the same value
as ShellResolvedSCC.''  And now I'm confused.
>I don't think, anybody ever checked or optimized it for slabs, so it
>might be, that the set is less optimal there. One would probably adjust
>the repulsive part, provided the band structure at the ab initio>geometry is reasonable.
I agree on this point, parameters are intended for cluster.I tried to optimize Fe32 and succesfully reproduced geometries from the literature.
All best,Branislav

On Tue, 31-01-2023 10:27, Benjamin Hourahine <benjamin.hourahine at strath.ac.uk> wrote:
> 






Hello Branislav,


> 


You
 could constrain the cell as being hexagonal (either Isotropic or FixAngles in the geometry optimiser), also did you use hexagonal appropriate k-points (Monkhorst-Pack grid shifts are different in this case)?


> 


Regards


> 


Ben



> 





       Dr. B. Hourahine, SUPA, Department of Physics,
> 
     University of Strathclyde, John Anderson Building,
> 
             107 Rottenrow, Glasgow G4 0NG, UK.
> 
     +44 141 548 2325, benjamin.hourahine at strath.ac.uk
> 

> 
2013/4 THE Awards Entrepreneurial University of the Year
> 
       2012/13 THE Awards UK University of the Year
> 

> 
    The University of Strathclyde is a charitable body,
> 
         registered in Scotland, number SC015263
> 








From: DFTB-Plus-User <dftb-plus-user-bounces at mailman.zfn.uni-bremen.de> on behalf of Bálint Aradi <aradi at uni-bremen.de>
> 
Sent: 31 January 2023 08:20
> 
To: dftb-plus-user at mailman.zfn.uni-bremen.de <dftb-plus-user at mailman.zfn.uni-bremen.de>
> 
Subject: Re: [DFTB-Plus-User] Bulk/slab Fe optimization problems using pbc-0-3 or trans3d-0-1 parameters
 


CAUTION: This email originated outside the University. Check before clicking links or attachments.
> 

> 
Dear Branislav
> 

> 
> I recompiled program and now I get reasonable structures.
> 

> 
That's a little bit worrisome, the results should not depend on the
> 
compilation on the program... If in doubt, try the official binaries via
> 
Conda, they should be OK.
> 

> 
> I tried two different setups for unit cell and got relatively good values:
> 
>
> 
> ShellResolvedSCC = Yes
> 
> ShellResolvedSpin = No
> 
>
> 
> Lattice parameter = 2.9338 A and nearest neighbor distance = 2.54078 A
> 
>
> 
> ShellResolvedSCC = No
> 
> ShellResolvedSpin = Yes
> 
>
> 
> Lattice parameter = 2.9393 A and nearest neighbor distance = 2.54553 A
> 

> 
Actually, I'd advise to set both, ShellResolvedScc as well as
> 
ShellResolvedSpin to "Yes".
> 

> 
> However, when I try to simulate 7x7x4 Fe(110) slab using LatticeOpt =
> 
> Yes and hexagonal symmetry I get quite distorted geometry.
> 
> Do you think this is just a parameter set inherited problem or maybe
> 
> DFTB+ is only good when using cubic symmetry?
> 

> 
DFTB+ itself does not care about symmetry at all. The problem is, for
> 
sure, parameter set related. I know, that the iron in the pbc set was
> 
tested on small iron clusters.
> 

> 
https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoi.org%2F10.1016%2Fj.chemphys.2004.03.034&data=05%7C01%7Cbenjamin.hourahine%40strath.ac.uk%7Ca30df178af7043c68b1f08db03641698%7C631e0763153347eba5cd0457bee5944e%7C0%7C0%7C638107500628267885%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=uX7B2fu58%2FyHlJk5yDDfkYf0fO1js5D%2Fl4ujuIboIos%3D&reserved=0
> 

> 
I don't think, anybody ever checked or optimized it for slabs, so it
> 
might be, that the set is less optimal there. One would probably adjust
> 
the repulsive part, provided the band structure at the ab initio
> 
geometry is reasonable.
> 

> 
Best regards,
> 

> 
Bálint
> 

> 

> 
--
> 
Dr. Bálint Aradi
> 
Bremen Center for Computational Materials Science, University of Bremen
> 
https://eur02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.bccms.uni-bremen.de%2Fcms%2Fpeople%2Fb-aradi%2F&data=05%7C01%7Cbenjamin.hourahine%40strath.ac.uk%7Ca30df178af7043c68b1f08db03641698%7C631e0763153347eba5cd0457bee5944e%7C0%7C0%7C638107500628267885%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=nj4nXPnjcEP477jBB9pKA%2FZcfkEcgOmvi3leRf1QHXc%3D&reserved=0
> 

> 

> 





        _______________________________________________
> DFTB-Plus-User mailing list
> DFTB-Plus-User at mailman.zfn.uni-bremen.de
> https://mailman.zfn.uni-bremen.de/cgi-bin/mailman/listinfo/dftb-plus-user
> 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.zfn.uni-bremen.de/pipermail/dftb-plus-user/attachments/20230201/b8fc043c/attachment.htm>