[QE-users] How to relax Fe(110) surface

[Gui Wei]

Hi,
When I relax Fe(110) surface ( 2 iron layers, the bottom layer is fixed),the caculation stoped with:convergence NOT achieved after 200 iterations.But when I add ‘nbnd=380' in the input file,the caculation end with :Total force = 0.001689 Total SCF correction = 0.001787 SCF correction compared to forces is large: reduce conv_thr to get better values.And bfgs converged in 1 scf cycles and 0 bfgs steps.So I reduce conv_thr from 1.0d-5 to 1.0d-10 and delete‘nbnd=380',I find it still does not converge.What is the role of nbnd and could I get a more reasonable result by adjusting some parameters?
 &control
    calculation  = 'relax',
    prefix='relaxFe1012',
    pseudo_dir = '/public/home/duan1/guiwei/QE/q-e-qe-6.3/pseudo/',
    outdir='/public/home/duan1/guiwei/QE/q-e-qe-6.3/tempdir/'
    tstress = .true.
    tprnfor = .true.
    etot_conv_thr=1.0D-3
    forc_conv_thr=1.0D-2   
/
 &system    
    ibrav= 0, 
    nat=60, 
    ntyp=1,
    nspin = 2 
    starting_magnetization(1) =0.4
    occupations='smearing',
    smearing='mp',
    degauss=0.02,
    ecutwfc =37.0
    ecutrho =240.0
    vdw_corr='DFT-D'     
    london_s6 = 0.75
/
&electrons
    conv_thr =  1.0d-5
    mixing_beta = 0.1
    mixing_mode = 'local-TF'
    mixing_ndim=16
    electron_maxstep=200
/
&IONS
  ion_dynamics='bfgs'
/
CELL_PARAMETERS angstrom
 19.67999  0.000000  0.000000
 0.000000  8.521686  0.000000
 0.000000  0.000000  17.00000
ATOMIC_SPECIES
Fe  55.847  Fe.pbe-n-kjpaw_psl.0.2.4.UPF
ATOMIC_POSITIONS  crystal
......
K_POINTS automatic
2  2  1  0  0  0





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