[Pw_forum] problem with vc-relax

[Eyvaz Isaev]

Dear Olga,

I could not reproduce the error you report using different  pw.x versions. 
They  finished by the error message (QE 4.2, compiler gfortran on Ubuntu 9.4 on 
my laptop, serial):
 
      from scale_h : error #         1
     Not enough space allocated for radial FFT: try restarting with a larger 
cell_factor.

Usually,   that means unreasonable lattice parameters. Say, one of them  is much  
larger than expected. In fact, this turned out to be dependent on  ecutwfc and 
pseudopotential type. The error persists for norm-conserving  type pseudo you 
used. But using US pseudo for C, and the cutoff energy  30Ry (360 for ecutrho) , 
no  problem arises. 

Besides, for Norm-conserving type pseudo for C 18Ry seems to be  extremely low. 
You can play around ecutwfc, upscale and cell_factor parameters. 

If you like, you can fix c-axis, do relax, and using a set of c-axis parameter  
find the minimum. 

 
Last, if you study a graphene sheet why you used 6 6 6? The correct one seems to 
be 6 6 1.

Bests,
Eyvaz.
 -------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, 
Sweden 

Theoretical Physics Department, Moscow State Institute of Steel & Alloys, 
Russia, 

isaev at ifm.liu.se, eyvaz_isaev at yahoo.com




________________________________
From: Olga Sedelnikova <o.sedelnikova at gmail.com>
To: pw_forum at pwscf.org
Sent: Tue, July 27, 2010 12:42:53 PM
Subject: [Pw_forum] problem with vc-relax


Dear All,
I have a problem with 'vc-relax' option for graphene. I have used david and cg 
diagonalization proceedures, different types of smearing and ion and cell 
dynamics but all calculations were crashed. 
One of my input file:
 
&CONTROL
     calculation = 'vc-relax',
     prefix = 'graphene',
     restart_mode='from_scratch'
     tstress=.true.,
     tprnfor=.true.,
     nstep=45,
      etot_conv_thr = 1.0E-4 ,
      forc_conv_thr = 1.0D-3 ,
      max_seconds = 36000 ,
      dt = 100,
   /
&SYSTEM
     ibrav = 4,
     celldm(1)= 4.64833
     celldm(3)=5.447621
               nat = 2, 
               ntyp = 1, 
               ecutwfc = 18.0,
               nbnd =8, 
     occupations='smearing'
     smearing = 'mv'
     degauss = 0.005
       /
&ELECTRONS
     conv_thr = 1.0d-7
     electron_maxstep = 70
     diagonalization='cg'
   /
&IONS
     ion_dynamics='damp'
/
&CELL
    cell_dynamics = 'damp-w' ,
    press=0.00 ,
    wmass=0.0015 ,
/
  
ATOMIC_SPECIES
     C   12.01100 C.pz-vbc.UPF
ATOMIC_POSITIONS crystal 
    C      0.00000000    0.00000000    0.50000000
    C      0.33333333    0.66666666    0.50000000
K_POINTS {automatic}
   6 6 6 0 0 0

Inthis cause: 
     
from electrons : error #         1
     charge is wrong

Maybe somebody has already dealed with this problem and can advice the correct 
options for graphene.
Any suggestion will be appreciated.

-- 
Best wishes,
Olga Sedelnikova
Nikolaev Institute of Inorganic Chemistry of SB RAS



      
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