[QE-users] Implementing a bias potential in a Si slab

[Helen Eisenberg]

Dear Users,

I am trying to implement a bias potential on a Si slab with a Li ion in 
the vacuum, and I am getting unphysical things happening to the Si slab 
(it gets squashed or stretched depending on which bias I use). This 
makes me think I'm doing something wrong...Do I need to use a dipole 
correction (dipfield=TRUE)? Am I doing something else wrong? Does it not 
work with molecular dynamics only ionic relaxation?

Thank you for your help (I have copied my input file below, note the 
various parameters, such as kpoints and ecutwfc are not yet converged, 
as these are initial calculations )

Dr. Helen Eisenberg,

Fritz Haber Center for Molecular Dynamics,

Hebrew University


&CONTROL
   calculation = "md",
   restart_mode='from_scratch',
   pseudo_dir  = "$PSEUDO_DIR",
   prefix      = "Energy_Si_2x2",
   tstress     = .true.
   tprnfor     = .true.
   outdir      = "$TMP_DIR"
dt=40,
nstep=800
tefield=TRUE
/
&SYSTEM
   ibrav       = 0,
   nat         = 33,
   ntyp        = 3,
   ecutwfc     = 28.D0,
   occupations = 'smearing',
   smearing    = 'mv',
   degauss     = 0.0001,
   tot_charge  = 0.0,
   nspin       = 2,
   starting_magnetization(1)=0.0
edir=3
emaxpos=0.9
eopreg=0.1
eamp=0.01
/
&ELECTRONS
electron_maxstep=500
  mixing_mode = 'plain'
   mixing_beta = 0.7
   conv_thr =  1.0d-6
/
  &ions
     pot_extrapolation='second-order'
     wfc_extrapolation='second-order'
  /

ATOMIC_SPECIES
Si  28.086  Si.pbe-mt_gipaw.UPF
H 1.00794 H.pbe-vbc.UPF
Li   6.941  Li.pbe-s-mt.UPF
ATOMIC_POSITIONS (crystal)
H 0.25  -0.00517        0 0 0 0
H 0.75  -0.00517        0 0 0 0
Si 0.51097      0.49804 0.16473
Si 0.35376      0.49734 0.35774
Si 0.25 0.24742 0.05541 0 0 0
Si 0.24944      0.24765 0.27061
Si 0.75 0.24742 0.05541 0 0 0
Si 0.75919      0.24761 0.28048
Si 6.33534E-4   0.49808 0.16495
Si 0.07141      0.49748 0.38744
Si -5.17962E-4  0.2482  0.10971
Si 0.01902      0.24763 0.33382
Si 0.75553      0.49764 0.22403
Si 0.50177      0.24816 0.10965
Si 0.4958       0.24746 0.33137
Si 0.25633      0.49758 0.21703
H 0.25  0.49483 0 0 0 0
H 0.75  0.49483 0 0 0 0
Si 0.51097      0.99804 0.16473
Si 0.35376      0.99734 0.35774
Si 0.25 0.74742 0.05541 0 0 0
Si 0.24944      0.74765 0.27061
Si 0.75 0.74742 0.05541 0 0 0
Si 0.75919      0.74761 0.28048
Si 6.33534E-4   0.99808 0.16495
Si 0.07141      0.99748 0.38744
Si -5.17962E-4  0.7482  0.10971
Si 0.01902      0.74763 0.33382
Si 0.75553      0.99764 0.22403
Si 0.50177      0.74816 0.10965
Si 0.4958       0.74746 0.33137
Si 0.25633      0.99758 0.21703
Li       0.625           0.5           0.5
K_POINTS automatic
2 2  1  0  0  0
CELL_PARAMETERS {angstrom}
                 7.6801695932    0.0000000000    0.0000000000
                 0.0000000000    7.76034    0.0000000000
                 0.0000000000    0.0000000000   24.5037250000
EOF