[Wien] Properties of corresponding atoms in afm calculations

[Ulrich Keßler]

I am running the newest version 06.04 on different platforms (Intel P4, 
AMD Athlon and Opteron). I did not check if the deviations are the same 
on different computers (for the same case).

Ulrich Keßler

Laurence Marks wrote:

>Which version are you running? Numerical errors can creep in which get
>inflated in mini because it (correctly) will diagnose small symmetry
>breaking as indicating a lower symmetry. Many, but not all of these
>have been trapped in the later versions.
>
>On 9/11/06, Ulrich Keßler <ukessler at uni-bonn.de> wrote:
>  
>
>>Dear Prof. Blaha,
>>
>>thank you for your answer.
>>
>>I think I did not describe my problem well enough.
>>
>>runafm seems not to be the problem. After an afm-cycle runsp does not
>>change anything significantly.
>>
>>My problem is that the forces of the corresponding atoms are not the
>>same. During a minimization cycle this leads to different shifts of the
>>corresponding atoms so that they are not any longer symmetry equivalent
>>in the ferromagnetic supergroup. At the moment I stop the miminization
>>after some cycles and edit the new struct file so that corresponding
>>atoms possess equivalent sites. In my opinion the equivalent atoms in
>>the supercell should have the same forces and should be shifted by the
>>same amount.
>>
>>This is what I did:
>>I constructed the afm supercell in P1121/c (SG 14) containing 12
>>independent atoms from the ferromagnetic structure in the supergroup
>>B112/b (SG 15, 6 independent atoms). Since this is a klassegleiche
>>subgroup the unit cell dimensions did not change. Every two atoms of
>>the afm structure in P21/c correspond and possess positions which are
>>equivalent in C2/c. During afminput I had to give the symmetry relation
>>between these corresponding atoms (simply 0.5, 0, 0.5 since the B
>>centering vanishes). After that runafm worked without problems except
>>for the different forces of the corresponding atoms (I did not check
>>other atom dependent properties).
>>
>>Is this something to live with (some kind of rounding error) or
>>something more serious? And does an afm calculatiom make sense when the
>>corresponding atoms are not mapped onto each other exactly by
>>case.inclmcopy?
>>
>>If you need more information (struct-files etc.) please let me know.
>>
>>Thank you for your help,
>>Ulrich Keßler
>>
>>Peter Blaha wrote:
>>
>>    
>>
>>>runafm and runsp should yield the same results, in particular when
>>>continuing with runsp AFTER a runafm convergence results must be
>>>identical. (The could be cases when
>>>runsp does not find and afm state, but eg. 2 moments which are different
>>>(ferrimagnetic),..)
>>>
>>>Maybe you have a problem with your struct file (symmetry) or with afminput
>>>(case.inclmcopy ?) ?
>>>
>>>
>>>
>>>
>>>
>>>      
>>>
>>>>when calculating an antiferromagnetic compound using the runafm_lapw
>>>>script, the symmetry relations between the antiferromagnetic atoms is
>>>>exploited (they share the same site in the ferromagnetic supergroup).
>>>>Thus I would expect that all properties of the corresponding atoms
>>>>should be the same, especially the forces. However, I find that the
>>>>forces of corresponding atoms tend to diverge in the course of an
>>>>afm-SCF-cycle (not much, but significantly). Even more so when
>>>>performing a minimization of positions.
>>>>
>>>>Is the reason some rounding error?
>>>>Is this serious? If yes, what could be done about it?
>>>>
>>>>Any comments are appreciated. Thank you.
>>>>
>>>>Ulrich Keßler
>>>>
>>>>
>>>>Dr. Ulrich Keßler
>>>>Institut für Anorganische Chemie
>>>>Universität Bonn
>>>>Gerhard-Domagk-Str. 1
>>>>D-53121 Bonn
>>>>Germany
>>>>Tel.: (+49) (0)228/73-5334
>>>>Fax: (+49) (0)228/73-5660
>>>>_______________________________________________
>>>>Wien mailing list
>>>>Wien at zeus.theochem.tuwien.ac.at
>>>>http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>>>
>>>>
>>>>
>>>>        
>>>>
>>>                                     P.Blaha
>>>--------------------------------------------------------------------------
>>>Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
>>>Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
>>>Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
>>>--------------------------------------------------------------------------
>>>_______________________________________________
>>>Wien mailing list
>>>Wien at zeus.theochem.tuwien.ac.at
>>>http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>>
>>>
>>>
>>>
>>>      
>>>
>>_______________________________________________
>>Wien mailing list
>>Wien at zeus.theochem.tuwien.ac.at
>>http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>
>>    
>>
>
>
>  
>