[QE-users] Question about optimizing the lattice constant of iron

[Stefano de Gironcoli]

cutoff might be too small for a reliable computation of the stress.

other than that I see no big issue in your input

stefano

On 25/12/18 04:35, Gui Wei wrote:
> Hi,
> When optimizing the lattice constant of bcc Fe,the result is a=2.830A， 
> which is in disagreement with experimentally derived structural 
> parameter a=2.863A.Could someone give me some advice?
>
> &CONTROL
>     calculation = 'vc-relax'
>     prefix='Fe1',
>     pseudo_dir = '/public/home/duan1/gw2/pseudo/',
> outdir='/public/home/duan1/gw2/tempdir/'
>     tprnfor     = .true.
>     tstress     = .true.
> /
> &SYSTEM
>     ibrav= 1,
>     A=2.8664
>     nat= 2
>     ntyp= 1
>     occupations='smearing',
>     smearing='mp',
>     degauss=0.02,
>     ecutwfc =37
>     ecutrho =240
>     nspin   = 2
>     starting_magnetization(1) = 0.4
> /
> &ELECTRONS
>     conv_thr        = 1.0d-8
>     mixing_beta      = 0.7
> /
> &IONS
>    ion_dynamics = 'bfgs'
> /
> &CELL
>    cell_dynamics = 'bfgs'
> /
> ATOMIC_SPECIES
> Fe  55.847 Fe.pbe-n-kjpaw_psl.0.2.4.UPF
> ATOMIC_POSITIONS crystal
>  Fe   0.0000000000000000  0.0000000000000000   0.0000000000000000
>  Fe   0.5000000000000001  0.5000000000000001   0.5000000000000001
> K_POINTS automatic
> 8  8  8  0  0  0
>
> The result:
>  CELL_PARAMETERS (alat=  5.41671099)
>    0.987418499   0.000000000  0.000000000
>    0.000000000   0.987418499  0.000000000
>    0.000000000   0.000000000  0.987418499
>
>
>
> Gui Wei
> School of Mechanical Engineering，Chongqing University, China
>
>
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