[Wien] why artificial lowering of symmetry changes the total energy?

[Stefaan Cottenier]

1) How large is your energy change? Perhaps it is just numerical noise?

2) If the change is large enough, and if it is a lowering of the  
energy upon symmetry reduction, you might have an onset of orbital  
ordering. Inspect the density matrices of the two inequivalent  
Cu-sites (dmat files), and see whether they are different from each  
other and/or different from the density matrix for the high-symmetry  
case. If there are differences, then this material apparently can  
lower its total energy by occupying the Cu-d orbitals in different  
ways in the two Cu-sites.

Stefaan


Quoting katrusiat <katrusiat at yandex.ru>:

> Dear all,
>
> I perform ferromagnetic (FM) (I make it FM by modifying the   
> case.inst file accordingly) GGA+U calculations of the total energy   
> of Cs2CuCl4, the compound with 4 equivalent magnetic Cu's in a unit   
> cell. When I create an artificial unit cell of a lower symmetry with  
>  2 inequivalent pairs of Cu's: Cu1 and Cu2, and again perform a FM   
> GGA+U calculation, the total energy of the system is slightly   
> different.
>
> By lowering the symmetry I only add labels to Cu's making them   
> inequivalent, and also the crystallographic axes are interchanged in  
>  the new unit cell. So, why after these seemingly harmless actions   
> the total energy should change?
>
> Thank you,
> Kateryna Foyevtsova
>
> --
> Яндекс.Почта. Поищите спам где-нибудь еще http://mail.yandex.ru/nospam
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-- 
Stefaan Cottenier
Computational Materials Engineering (CME) &
Center for Computational Engineering Science (CCES)
RWTH Aachen University
Mauerstrasse 5
DE-52064 Aachen
Germany

e-mail: stefaan.cottenier at fys.kuleuven.be (preferred)
         cottenier at ghi.rwth-aachen.de (avoid)


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