[Pw_forum] vc-relax of graphite

[li niu]

dear Paolo,
  
Thanks for your help.
In the paper that "The phonon dispersion of graphite revised [Solid State Communication 131 (2004) 141-152] ", there is a sentence that"For a meaningful comparison of phonon frequencies obtained by different calculations( using different pseudopotentials, basis-sets,parameteriations of the exchange-correlation functional), each calculation should be performed at the respective optimized lattice constant."
So I tried to optimize lattice constant for graphite but always met errors.
You said the good old way: fix c to the experimental value and only optimize a.
How to excecute in the code?
  
Thanks in advance!
   
  Niu Li
  ==================================================
  My input as follows:
cat > graphite.vcrx.in << EOF
&CONTROL
  calculation  = "vc-relax",
  prefix       = "graphite",
  pseudo_dir   = "$PSEUDO_DIR",
  outdir       = "$TMP_DIR",
  tstress = .true. ,
  tprnfor = .true. ,
                       nstep = 65 ,
               etot_conv_thr = 1.0E-4 ,
               forc_conv_thr = 1.0D-3 ,
                          dt = 100 ,
/
&SYSTEM
    ibrav = 4, 
    celldm(1) =4.6336, 
    celldm(3)=2.7243,
    nat= 4, ntyp= 1,
    ecutwfc =40  
/
&ELECTRONS
   conv_thr    = 1.D-9,
  mixing_beta = 0.7D0,
/
&IONS
  pot_extrapolation = "second_order",
  wfc_extrapolation = "second_order",
/
&CELL
               cell_dynamics = 'damp-w',
                       press = 0.0 ,
                       wmass = 0.010 ,
 /
ATOMIC_SPECIES
 C   12.0107  C.pz-vbc.UPF
  ATOMIC_POSITIONS {crystal}
 C  0.0000000 0.0000000 0.0000000 
 C  0.0000000 0.0000000 0.5000000
 C  0.6666667 0.3333333 0.0000000
 C  0.3333333 0.6666667 0.5000000
K_POINTS automatic
16 16 6 1 1 1
  EOF
$ECHO " optimizing the lattice constant for bulk graphite...\c"
$PW_COMMAND < graphite.vcrx.in > graphite.vcrx.out
$ECHO " done"




 		
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