[Pw_forum] Is the Graphite surface flate?

[Masoud Nahali]

Dear Quantum Espresso users

I optimized the graphite bulk and the
 layers were completely flat. But when I try to "relax" the graphite 
surface (slab 2*2 with 3 monolayer) with 10 angstrom vacuum all the layers 
become extremely ripple!!! I can not find the problem. May it related to the number of layers? anyhow the number of layers is like the bulk. Your help would 
be a great gift.

input file:

&CONTROL
  
calculation  = "relax",
  pseudo_dir   = 
"/home/koa/soft/qe4.2/espresso-4.2/pseudo",
  outdir       = 
"/home/koa/tmp",
  etot_conv_thr= 1.0D-4,
  forc_conv_thr= 1.0D-3,
 
 nstep=150,
  /
&SYSTEM
  ibrav     = 4,
  a         = 
4.9318,
  b         = 4.9318,
  c         = 16.7029,
  
cosab     = -0.5,
  cosac     = 1.0,
  cosbc     = 1.0,
  
nat       = 24,
  ntyp      = 1,
  ecutwfc   = 40.D0,
  
ecutrho   = 400.D0,
  occupations = 'smearing'
  smearing ='mp', 
 
 degauss = 0.01,
  nspin = 2,
  starting_magnetization(1)= 1.0,
 
 /
&ELECTRONS
  conv_thr    = 1.D-6,
  mixing_beta = 0.7D0,
 
 diagonalization = "david",
/
&IONS
 ion_dynamics="bfgs"
/
ATOMIC_SPECIES
C 
 12.0107  C.star1s-pbe-rrkjus.UPF
ATOMIC_POSITIONS {angstrom}
C   
 0.000000    0.000000    0.000000
C    2.465900    0.000000    
0.000000
C    -1.232950    2.135532    0.000000
C    1.232950    
2.135532    0.000000
C    0.000000    1.423688    0.000000
C    
-1.232950    3.559220    0.000000
C    2.465900    1.423688    
0.000000
C    1.232950    3.559220    0.000000
C    0.000000    
0.000000    3.351450
C    2.465900    0.000000    3.351450
C    
-1.232950    2.135532    3.351450
C    1.232950    2.135532    
3.351450
C    1.232950    0.711844    3.351450
C    0.000000    
2.847376    3.351450
C    3.698850    0.711844    3.351450
C    
2.465900    2.847376    3.351450
C    0.000000    0.000000    
6.702900
C    2.465900    0.000000    6.702900
C    -1.232950    
2.135532    6.702900
C    1.232950    2.135532    6.702900
C    
0.000000    1.423688    6.702900
C    -1.232950    3.559220    
6.702900
C    2.465900    1.423688    6.702900
C    1.232950    
3.559220    6.702900
K_POINTS {automatic}
4 4 1 1 1 1


out
 put (optimized positions):

C        0.000000000  
-0.000000000  -0.686394528
C        2.465900000  -0.003714144  
-0.758610095
C       -1.229733457   2.137389072  -0.758610095
C       
 1.229733457   2.137389072  -0.758610095
C        0.000000000   
1.427474855  -0.213813075
C       -1.229670488   3.557326573  
-0.213813075
C        2.465900000   1.423688000  -0.285079086
C       
 1.229670488   3.557326573  -0.213813075
C       -0.000000000   
0.000000000   3.630366631
C        2.465900000  -0.014904710   
3.544792504
C       -1.220042143   2.142984355   3.544792504
C       
 1.220042143   2.142984355   3.544792504
C        1.220249305   
0.704511250   3.106073641
C        0.000000000   2.847376000   
3.022325711
C        3.711550695   0.704511250   3.106073641
C       
 2.465900000   2.862041499   3.106073641
C        0.000000000   
0.000000000   7.468882932
C        2.465900000   0.008344370   
7.466151214
C       -1.240176436   2.131359815   7.466151214
C       
 1.240176436   2.131359815   7.466151214
C        0.000000000   
1.414904155   6.963129179
C       -1.240557033   3.563611923   
6.963129179
C        2.465900000   1.423688000   6.961528237
C       
 1.240557033   3.563611923   6.963129179



Many Thanks
Masoud Nahali
Sharif
 University of Technology
 		 	   		  
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