[Pw_forum] GGA not converge

[Giuseppe Mattioli]

Dear Sakhraoui

Open shell metallic system may be very nasty... But there are some parameters of your calculation 
that should improve the convergence

>     ecutwfc = 20,

Your pseudopotential are ultrasoft, but they contains semicore electrons. I expect a wfc convergence 
threshold of 35~40 Ry. Moreover, if you do not indicate an ecutrho value, it is fixed by default at 
ecutwfc*4, which is a good choice for norm conserving PPs. You should try to indicate an ecutrho 
value; somewhere between ecutwfc*6 and ecutwfc*10.

> mixing_beta = 0.5,

When the davidson diagonalization fails, first try to lower the mixing_beta, even at very low values 
(i.e., 0.05). If it fails again, then try the (time consuming) cg diagonalization.

>     smearing='mv',

The 'gaussian' smearing converges more easily. You may start a further 'mv' calculation after the 
end of a 'gaussian' one.

HTH

Giuseppe


On Wednesday 07 November 2012 09:33:50 Sakhrawi Taoufek wrote:
> Dear all
> 
> i am calculating the lattice parameter for antiferromagnetic FeRh, it
> dosen't converge. ###############################&control
>     prefix='FeRh_afm',
>     pseudo_dir = '***/',
>     outdir='***/'
>  /
>  &system
>     ibrav= 0,    celldm(1) =$alat,
>     nat=4,    ntyp=3,
>     ecutwfc = 20,
>     occupations='smearing',
>     smearing='mv',
>     degauss=0.02,
>     nspin=2,
>     starting_magnetization(1)= 0.3,
>     starting_magnetization(2)= -0.3,
>     starting_magnetization(3)=  0.0,
>   /
>   &electrons
> mixing_mode = 'plain' ,
> mixing_beta = 0.5,
> diagonalization = 'david' ,
> conv_thr = 1.0d-7,
> electron_maxstep=1000,
>  /
> CELL_PARAMETERS {cubic}
>    1.0000   0.0000   0.0000
>    0.0000   1.0000   0.0000
>    0.0000   0.0000   1.0000
> ATOMIC_SPECIES
>  Fe1 55.85    Fe.pbe-spn-rrkjus.UPF
>  Fe2 55.85    Fe.pbe-spn-rrkjus.UPF
>  Rh 102.91    Rh.pbe-spn-rrkjus.UPF
> ATOMIC_POSITIONS {crystal}
>    Fe1      0.00000000  0.00000000  0.00000000
>    Fe2      0.50000000  0.50000000  0.50000000
>    Rh       0.25000000  0.25000000  0.25000000
>    Rh       0.75000000  0.75000000  0.75000000
> K_POINTS {automatic}
>    10 10 10 1 1 1
> 
> ###############################
> see the attached file please.
> any suggestion will be appraciated.
> --------------------------------
> 
> Sakhraoui Taoufik
> Ph.D student
> Faculty of Sciences of Monastir
> Department of Physics
> L.M.C.N
> Monastir, Tunisia
> --------------------------------

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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
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