[Pw_forum] SCF convergency

[Eyvaz Isaev]

Hi,

Hopefully you know that celldm(1)=15.8321 is in atomic
units, but not Angstrom. 

You asked to do spin-polarized calculations (nspin=2),
but put initial magnetic splitting  to zero.
So, you have to change  
starting_magnetization(1) = 0.9 and add more 2 same
lines for Cr and O atoms (your first atomic type is
Fe). Presumably, you should not specify the bands
number, so, remove nbnd=330. Be careful with this
number, it means that you have around 600-660
electrons in your crystal.  If you are sure that your
nbnd covers bands above the Fermi level,then it is OK.


Ecutrho seems to be low, increase up to 200Ry.
Try mixing_beta=0.1.
degauss=0.5? It is very large. Try degauss=0.03, it is
in Ry.  
To me conv_thr=1.d-5 seems too large. Default conv_thr
(1d-6) looks more acceptable. 

Finally, if something went OK, be ready for LDA+U
calculations. Fe-Cr-O looks like a strongly correlated
system.

Best regards,
Eyvaz.
 
> &system
>     ibrav = 1, celldm(1) = 15.8321, nat = 56, ntyp =
> 3
>     nbnd = 330
>     nspin = 2, degauss = 0.5
>     occupations = 'smearing'
>     smearing = 'gaussian'
>     starting_magnetization(1) = 0.0
>     ecutwfc = 25.0
>     ecutrho = 140.0
> /
> &electrons
>     diagonalization = 'cg'
>     mixing_mode = 'plain'
>     mixing_beta = 0.40
>     conv_thr = 1.0d-5
> /
> 
> ATOMIC_SPECIES
> Fe  55.847	Fe.pbe-sp-van.UPF
> Cr  51.996	Cr.pbe-sp-van.UPF
> O   15.999	O.pbe-van_ak.UPF
> 
> ATOMIC_POSITIONS angstrom
> Fe    0.00000	 0.00000    0.00000
> Cr    5.23625	 5.23625    5.23625
> O    3.23391	 3.23391    3.23391
> Fe    0.00000	 4.18900    4.18900
> Fe    4.18900	 0.00000    4.18900
> [...]
> 
> K_POINTS automatic
> 1 1 1 0 0 0
> 
> 
> I have sent this mail three times with a graph
> attached. The first two posts 
> had been rejected
> because size of the mail was a little larger than
> the limit. The third one 
> should be below 40KB,
> but I haven't seen its appearing on the list yet.
> So, I have to post it 
> again without a graph. I
> apologize for that you may receive two mails with
> similar content.
> 
>
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