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

[Gui Wei]

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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