[Pw_forum] how to make scf converged for a (3,0) CNT?

[Zhu Xi]

Hi PW users,
I can't make the scf converged for a (3.0) CNT, can anyone give some advice?
Thanks!

the input is
++++++++++++++++++++++++++++++++++++++++++
&control
         calculation='relax',
         PSEUDO_DIR='./',
          restart_mode='from_scratch',
         prefix='cnt30',
         forc_conv_thr=1.0D-4,
         outdir='./' ,
          wf_collect=.true. ,
        /
&SYSTEM
         ibrav = 0,
         celldm(1)=0,
         nat = 12,
         ntyp = 1,
         ecutwfc = 30.0 ,
         ecutrho = 300,
         nbnd = 30,
/
&electrons
        conv_thr    = 1.D-6,
        mixing_beta = 0.2,
/
&IONS
 ion_dynamics = 'damp'
/
CELL_PARAMETERS
8.0502333261  0.0  0.0
 0.0 18.897261329  0.0
 0.0  0.0 18.897261329
ATOMIC_SPECIES
    C    12.00000 C.pz-rrkjus.UPF
ATOMIC_POSITIONS (crystal)
C   0.8333333333333349   0.5587165273624200   0.3982999913642820
C   0.3333333333333350   0.4412834726375799   0.6017000086357180
C   0.6666666666666640   0.4412834726375799   0.3982999913642820
C   0.3333333333333350   0.4412834726375799   0.3982999913642820
C   0.6666666666666640   0.4412834726375799   0.6017000086357180
C   0.8333333333333349   0.5587165273624200   0.6017000086357180
C   0.6666666666666640   0.6174330547248399   0.4999999999999999
C   0.3333333333333350   0.6174330547248399   0.4999999999999999
C   0.8333333333333349   0.3825669452751600   0.4999999999999999
C   0.1666666666666630   0.5587165273624200   0.6017000086357180
C   0.1666666666666630   0.5587165273624200   0.3982999913642820
C   0.1666666666666640   0.3825669452751600   0.4999999999999999
K_POINTS {automatic}
21 1 1 0 0 0
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++




the out put is
============================================================
     ethr =  1.21E-06,  avg # of iterations =  1.0

     negative rho (up, down):  0.642E-04 0.000E+00

     total cpu time spent up to now is      0.62 secs

     total energy              =  -135.75618000 Ry
     Harris-Foulkes estimate   =  -135.75624906 Ry
     estimated scf accuracy    <     0.01236748 Ry

     End of self-consistent calculation

     convergence NOT achieved, stopping

     Writing output data file cnt30.save

     PWSCF        :  0m 0.62s CPU time,    57m23.48s wall time

     init_run     :     0.00s CPU
     electrons    :     0.62s CPU
=================================================================


compiler flag is -O2 -axW by ifort10.1015 and mpich2.1.08
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