[QE-users] Proper setup for organometalic system ....

[Giuseppe Mattioli]

Dear Michal
open-shell metal complexes usually show instabilities in scf cycles.  
This may be generally due to jumps between almost equivalent or  
degenerate electronic states, but also to the strongly correlated  
nature of d electrons weakly coupled with the ligand electronic states  
(a typical Mott-Hubbard problem...!), with the delocalization error  
leading to a wrong "metallic" description of the partially occupied d  
band. In the former case, there is no harm in using  
occupations='smearing' with a Gaussian smearing to facilitate  
convergence, as long as the smearing is small enough to avoid the  
spread of electrons across the HOMO-LUMO gap. You can even use  
tot_magnetization to force the convergence to any sensible magnetic  
configuration of the system. In the latter case, you should be almost  
always able to reach the converge using a Gaussian smearing, but you  
should closely check the results and maybe use some local (e.g. DFT+U)  
or global (e.g. EXX functionals like B3LYP, PBE0, ...) correction to  
improve the description of the system.
HTH
Giuseppe

Quoting Michal Husak <Michal.Husak at vscht.cz>:

> Hi alll
>
> I was up to now working with fully organic system - so I handled  
> then with fixed occupany ...
>
> I was working with:
> OCCUAPTIONS: fixed
>
> I need to work now with organometalic systems - they contain group  
> like e.g. Fe O6 (iron coordinated by 6 oxygen + organic parts) ...
>
> I belive it is still an insulator, but the fixed occupancy lead to  
> non-converging SCF (oscillating between 2 states) ...
>
> Can anybody tell me what everything do i need to change in the setup  
> to handle organometalic compounds ?
>
> Is simple following modification everything I need to do ?:
>
> OCCUAPTIONS: smearing
>
> Michal Husak
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GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.mattioli at ism.cnr.it>