[Wien] Freestanding Pb slab calculation

Tue Sep 7 16:00:07 CEST 2010

Dear users,

I am trying to calculate the band structure of a free standing Pb slab
of 6 ML thickness and 12 ML of vacuum for different lattice parameter.
Starting with a =4.95 Å the SCF cylce converges, but  my band structure
along M-G-M looks strange, thats why I need help in order to fix the
problem.

Let me brievely review the steps I have done so far to obtain a band
structure.

1.) Generation of slab geometry
a) Pb unit cell, with lattice a=4.95Å, lattice type:F
b) slab generation using octave
     i) s=loadstruct("Pb495.struct");
     ii) s1 = makeconventional(s);
     iii) s2 = makesurface(s1, [1 1 1],1,34,67) (film thickness = 34 bohr
= 6 ML, vacuum thickness = 68 bohr = 12 ML)
     iv) savestruct(s2,"Pb_slab.struct","P1");
     After copying the Pb_slab.struct to Pb495.struct "Structgen" shows a
spacegroup: 1P1_ , 22 inequivalent atoms, 1 symmetry         operation

2.) Initialization of the struct
     i) nn-bondlength factor 2 (default)-->here I get a warning: WARNING:
Mult not equal. PLEASE CHECK outputnn-file
     ii) I ignored the warning and did not used the new struct_nn file
     iii) After x sgroup (0.001u 0.001s 0:00.00 0.0%    0+0k 0+0io 0pf+0w)
     I get the warning:
     warning: !!! Number of inequivalent atoms has changed. !!! Old
value= 22 New value= 12 warning: !!!
     Bravais lattice has changed. sgroup found: 156 (P 3 m 1) Note that
shift vectors for this space group are defined
     which I also ignored
iv) x symmetry gives: alpha(3) .lt. 89.8; reset to 90.1 0.003u 0.002s
0:00.00 0.0%    0+0k 0+0io 0pf+0w
So far I did not accept a new struct file
v) x lstart gives with -6.0 Ry a core electron leak of 0.010, and 7.0
also, but at 8.0 Ry I got no warning.
the case.inst file
vi) for the first SCF run I lowered the R*kmax value to 5.0 instead of
7.0 and choosed TEMP as Fermi method with eval = 0.005 (as proposed by
robert)
vii) in x kgen I set the grid to 4x4x1 and got the message:
1  symmetry operations without inversion
  inversion added (non-spinpolarized non-so calculation)
viii) the x dstart is always automatically marked as "interactively
complex selected" although  it was said that inversion was added.
Anyway I started x dstart -c and got: 14.215u 3.626s 0:18.03 98.8%
0+0k 0+0io 0pf+0w

ix) after choosing "no-spin polarization" I start a SCF cycle with
following criteria:
Energy = 0.0001 Ry and Charge = 0.001 e

After 19h of calculation and 30 cycles the convergency is reached to
Energy = 0.00015 and charge -0.0009, I save the lapw using save_lapw.

In files/error files I got a message: Error in LAPW1, but only there,
because the dayfile says nothing about errors:

  >   stop

ec cc and fc_conv 1 1 1
:CHARGE convergence:  1 0.001 -.0009186
:ENERGY convergence:  1 0.0001 .0000157900000000
  >   mixer    (14:16:04) 3.840u 1.244s 0:11.53 44.0%    0+0k 0+131960io
0pf+0w
  >   lcore    (14:15:53) 0.672u 0.204s 0:02.08 41.8%    0+0k 0+26048io
0pf+0w
  >   lapw2 -c       (14:14:06) 97.114u 7.196s 1:47.02 97.4%    0+0k
0+135112io 0pf+0w
  >   lapw1  -c      (13:40:11) 2016.750u 6.508s 33:55.25 99.4%    0+0k
0+1144152io 0pf+0w
  >   lapw0     (13:37:00) 184.023u 1.468s 3:10.82 97.2%    0+0k
0+85080io 0pf+0w

3) Then I start to calculate the bandstructure creating a cut along
M-G-M with 40 k-points: x lapw1 -band -c

I have almost no experience in performing DFT, except some which I got
in the workshop in Nantes. But there everything was fine :) Now I run
into several problems, as you can see.

Perhabs an experience user will see immediately that soemthing bad happens.

Because I still run lapw1 -band -c I will provide the calculated band
structure later (if somebody is interested). For now I need a red line,
what files I should check or any other hint.

Thanks and best regards,

Bartosz

-- 
Bartosz Slomski
------------------------------------------
Swiss Light Source, Paul Scherrer Institut
WSLA/205
CH-5232 Villigen PSI, Switzerland
Tel: +41 (0)56 310 5694
------------------------------------------
Physik-Institut, Universität Zürich
Winterthurerstr. 190
CH-8057 Zurich, Switzerland
Tel: +41 (0)44 635 5824

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