[Pw_forum] odd energy behavior for H/LiF

[Gisela Bocan]

Hello,
         I am trying to study the H/LiF(001) system, my first insulating
surface. When I calculate the energy as a function of the H-LiF surface I
obtain an odd shoulder around 5 bohr (see figure attached). I am
considering an 8 layer slab, around 30 bohr of vacuum between slabs, a
sqrt(2)xsqrt(2) surface cell, pbe rrkjus US pseudopotentials for all three
elements with Li semicore electrons included. Is this behavior expected for
an ionic insulating surface? Or is there a problem with my input file? I am
setting:

&control
   prefix      = 'F',
   outdir      = '/home/myoutdir',
   pseudo_dir  = '/home/mypseudo',
   calculation = 'scf',
   lkpoint_dir = .false.,
   verbosity   = 'high',
   nstep       = 1,
/
&system
   ibrav       = 8,
   celldm(1)   = 7.6899999999999995,
   celldm(2)   = 1.0000000000000000,
   celldm(3)   = 7.5000000000000009,
   nat         = 33,
   ntyp        = 3,
   ecutwfc     = 100,
   ecutrho     = 500,
   occupations = 'smearing',
   smearing    = 'gaussian',
   degauss     = 0.0001,
   nspin       = 2,
   starting_magnetization(1) = 0.
   starting_magnetization(2) = 0.
   starting_magnetization(3) = 1.
/
&electrons
   conv_thr = 1.d-6,
   diagonalization = 'cg',
   mixing_mode = 'plain',
   mixing_beta = 0.7D0,
/
ATOMIC_SPECIES
   F   18.9984032  F.pbe-n-rrkjus_psl.0.1.UPF
   Li  6.941       Li.pbe-s-rrkjus_psl.0.2.1.UPF
   H   1.00794     H.pbe-rrkjus_psl.0.1.UPF
ATOMIC_POSITIONS crystal
   H   0 0 0.5013437   0  0  0
   F   0.00 0.00 0.46666667   0  0  0
   Li  0.50 0.00 0.46666667   0  0  0
   Li  0.00 0.50 0.46666667   0  0  0
   F   0.50 0.50 0.46666667   0  0  0
   Li  0.00 0.00 0.40000000   0  0  0
   F   0.50 0.00 0.40000000   0  0  0
   F   0.00 0.50 0.40000000   0  0  0
   Li  0.50 0.50 0.40000000   0  0  0
   F   0.00 0.00 0.33333333   0  0  0
   Li  0.50 0.00 0.33333333   0  0  0
   Li  0.00 0.50 0.33333333   0  0  0
   F   0.50 0.50 0.33333333   0  0  0
   Li  0.00 0.00 0.26666667   0  0  0
   F   0.50 0.00 0.26666667   0  0  0
   F   0.00 0.50 0.26666667   0  0  0
   Li  0.50 0.50 0.26666667   0  0  0
   F   0.00 0.00 0.20000000   0  0  0
   Li  0.50 0.00 0.20000000   0  0  0
   Li  0.00 0.50 0.20000000   0  0  0
   F   0.50 0.50 0.20000000   0  0  0
   Li  0.00 0.00 0.13333333   0  0  0
   F   0.50 0.00 0.13333333   0  0  0
   F   0.00 0.50 0.13333333   0  0  0
   Li  0.50 0.50 0.13333333   0  0  0
   F   0.00 0.00 0.06666667   0  0  0
   Li  0.50 0.00 0.06666667   0  0  0
   Li  0.00 0.50 0.06666667   0  0  0
   F   0.50 0.50 0.06666667   0  0  0
   Li  0.00 0.00 0.00000000   0  0  0
   F   0.50 0.00 0.00000000   0  0  0
   F   0.00 0.50 0.00000000   0  0  0
   Li  0.50 0.50 0.00000000   0  0  0
K_POINTS automatic
   3 3 1  1 1 1

For testing purposes, I am using an unrelaxed LiF surface.

Any help and/or suggestion will be greatly appreciated. I myself am quite
at a loss...:-(

Gisela.
Surface Physics Group
Centro Atómico Bariloche
Argentina
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