[Pw_forum] pp.x stm constant current mode

[Sun Tao]

Dear All:

I am trying to learn about calculating stm image with constant current mode
with pp.x. The following is the input from example03 of pp.x.


############# first is scf part ###############

 &control
    calculation = 'scf'
    restart_mode='from_scratch',
    title='AlAs 110 surface slab, relaxed (central plane fixed)'
    pseudo_dir = './',
    outdir='./',
    prefix='AlAs110'
 /
 &system
    ibrav=  8, celldm(1) =7.424621202, celldm(2)=1.414213576,
    celldm(3)= 6.00000,
    nat= 14, ntyp= 2,
    ecutwfc =14.0,
 /
 &electrons
    mixing_mode = 'plain'
    mixing_beta = 0.7
    conv_thr =  1.0d-6
 /
 ATOMIC_SPECIES
 Al  26.98  Al.pz-vbc.UPF
 As  74.92  As.pz-bhs.UPF
ATOMIC_POSITIONS
 As  0.000000000  -0.044777195  -0.058158722
 Al  0.500000000   0.251460333   0.113525468
 As  0.500000000   0.712279009   0.504183885
 Al  0.000000000   1.067633546   0.480460620
 As  0.000000000  -0.003937059   0.995826731
 Al  0.500000000   0.351400965   1.004220212
 As  0.000000000  -0.003937059   2.004173269
 Al  0.500000000   0.351400965   1.995779788
 As  0.500000000   0.712279009   2.495816115
 Al  0.000000000   1.067633546   2.519539380
 As  0.000000000  -0.044777195   3.058158722
 Al  0.500000000   0.251460333   2.886474532
 As  0.500000000   0.707106800   1.500000000
 Al  0.000000000   1.060660200   1.500000000
K_POINTS {automatic}
 6 2 1 0 0 0

############### then is the non scf part #############

 &control
    calculation = 'nscf'
    restart_mode='from_scratch',
    title='AlAs 110 surface slab, relaxed (central plane fixed)'
    pseudo_dir = './',
    outdir='./',
    prefix='AlAs110'
 /
 &system
    ibrav=  8, celldm(1) =7.424621202, celldm(2)=1.414213576,
    celldm(3)= 6.00000,
    nat= 14, ntyp= 2,
    occupations='smearing', smearing='gaussian', degauss=0.01, nbnd=34,
    ecutwfc =14.0,
 /
 &electrons
    mixing_mode = 'plain'
    mixing_beta = 0.7
    conv_thr =  1.0d-6
 /
 ATOMIC_SPECIES
 Al  26.98  Al.pz-vbc.UPF
 As  74.92  As.pz-bhs.UPF
ATOMIC_POSITIONS
 As  0.000000000  -0.044777195  -0.058158722
 Al  0.500000000   0.251460333   0.113525468
 As  0.500000000   0.712279009   0.504183885
 Al  0.000000000   1.067633546   0.480460620
 As  0.000000000  -0.003937059   0.995826731
 Al  0.500000000   0.351400965   1.004220212
 As  0.000000000  -0.003937059   2.004173269
 Al  0.500000000   0.351400965   1.995779788
 As  0.500000000   0.712279009   2.495816115
 Al  0.000000000   1.067633546   2.519539380
 As  0.000000000  -0.044777195   3.058158722
 Al  0.500000000   0.251460333   2.886474532
 As  0.500000000   0.707106800   1.500000000
 Al  0.000000000   1.060660200   1.500000000
K_POINTS {automatic}
 12 4 1 0 0 0

################# then is the stm constant current part ##########

 &inputpp
    prefix  = 'AlAs110'
    outdir='./',
    filplot = 'AlAsresm+1.0'
    sample_bias=0.0735d0,
    plot_num= 5
 /
 &plot
    nfile=1
    filepp(1)='AlAsresm+1.0'
    weight(1)=1.0
    iflag=2
    output_format=3
    fileout='AlAs110.pp_isostm+.XSF'
    e1(1)=7.0, e1(2)=0.0,     e1(3)=0.0
    e2(1)=0.0, e2(2)=7.07107, e2(3)=0.0
    nx=150, ny=150
    isostm_flag=.true.
    isovalue=0.00005
    heightmin=0.4
    heightmax=0.75
    direction=1
 /

The result I have obtained is very strange. The input file already shows
"heightmin = 0.4" and "heightmax = 0.75", so I am thinking the output
produces the z coordinates for those points agreeing isovalue of 0.00005
and within the range Z*(0.4~0.75) (Z is the length of z dimension of the
box).  I suppose that the output I have should be between 23.573641935*0.4
to 23.573641935*0.75, where 23.573641935 is the z dimension of the box.
However, the output shows:

Min, Max, imaginary charge:   -17.455569   73.879219    0.000000

which already exceed the values I expect. I am totally lost about that it
produces in the output file.

Could somebody help me with this? Thanks very much ~

Tao



-- 
Tao Sun (Victor)
Graduate student
Department of Mechanical Science and Engineering
University of Illinois at Urbana-Champaign (UIUC)
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