[Pw_forum] Trouble with SCF calculation in PW

[Steven Kirk]

Hello,

I'm trying to get a simple single-point calculation from the PW input 
file shown below. I want to use an ultrasoft potential 
(C.pbe-rrkjus.UPF), but when I try to use that, the program stops in 
cdiagh and gives me a cryptic error #131.

So I switch to something simpler (C.blyp-mt.UPF) and at least the 
program seems to be doing SCF iterations now. But after the 11th 
iteration, things seem to go wrong (est. change leaps up to < 0.9 Ry, 
never really settles back, and the calculation runs out of iterations ).

The structure should look like a slightly squashed nanotube.

Can anyone tell me what I'm doing wrong ? I have taken the fractional 
coordinates straight from a CIF file which looks fine when I preview it.

The pseudopotentials used were downloaded straight from the website.

Many thanks in advance,

Steve Kirk

===== PW input file follows ======
&control
    calculation='scf'
    restart_mode='from_scratch',
    title='Trial scf run on 8_25 structure',
    prefix='8_25',
    pseudo_dir='/home/steve/pwscf1.3/pseudo//',
    outdir = '/home/steve/pwscf1.3/8_25//'
  /
  &system
    ibrav=8,
    A = 14.0289, B = 11.2105, C = 4.216681, COSAB = 0, COSAC = 0, COSBC = 0,
    nat = 32,
    ntyp = 1,
    ecutwfc = 36.749309
  /
  &electrons
  /
  ATOMIC_SPECIES
  C 12.0107 C.blyp-mt.UPF
  ATOMIC_POSITIONS crystal
  C   0.23321806    0.10541259  -0.83477178
  C   0.08680611    0.21666170  -0.83347361
  C  -0.08680611    0.21666170  -0.83347361
  C  -0.23321806    0.10541259  -0.83477178
  C  -0.23321806   -0.10541259  -0.83477178
  C  -0.08680611   -0.21666170  -0.83347361
  C   0.08680611   -0.21666170  -0.83347361
  C   0.23321806   -0.10541259  -0.83477178
  C   0.16896599    0.17979883  -0.66617051
  C   0.00000000    0.22347250  -0.66665291
  C  -0.16896599    0.17979883  -0.66617051
  C  -0.25898970    0.00000000  -0.66448979
  C  -0.16896599   -0.17979883  -0.66617051
  C   0.00000000   -0.22347250  -0.66665291
  C   0.16896599   -0.17979883  -0.66617051
  C   0.25898970    0.00000000  -0.66448979
  C   0.16896599    0.17979883 	0.66617051
  C   0.00000000    0.22347250 	0.66665291
  C  -0.16896599    0.17979883 	0.66617051
  C  -0.25898970    0.00000000 	0.66448979
  C  -0.16896599   -0.17979883 	0.66617051
  C   0.00000000   -0.22347250 	0.66665291
  C   0.16896599   -0.17979883 	0.66617051
  C   0.25898970    0.00000000 	0.66448979
  C   0.23321806    0.10541259 	0.83477178
  C   0.08680611    0.21666170 	0.83347361
  C  -0.08680611    0.21666170 	0.83347361
  C  -0.23321806    0.10541259 	0.83477178
  C  -0.23321806   -0.10541259 	0.83477178
  C  -0.08680611   -0.21666170 	0.83347361
  C   0.08680611   -0.21666170 	0.83347361
  C   0.23321806   -0.10541259 	0.83477178
  K_POINTS gamma
====== PW input file ends ======