[Pw_forum] Cell optimization converges to unrealistic value

[Yury Vishnevskiy]

Dear QE users,
I have a problem with cell optimization for one of my objects -- Copper 
phthalocyanine. It has layered structure and the distance between sheets 
must be around 3.3 Angstroms according to some experimental evidences. 
Using this value as an initial approximation I've started "vc-relax" 
calculation with pw.x from the latest version of the QE package (5.0). 
The calculation died several times after 15-20 optimization cycles with 
message

"Error in routine scale_h (1):
      Not enough space allocated for radial FFT: try restarting with a 
larger cell_factor."

and I restarted it using latest optimized parameters. During the 
optimization the distance between layers (parameter celldm(3)) got 
unrealistically small. Now it is around 0.5 Angstrom. What could be 
wrong with my input (see below)?

  &control
     calculation = 'vc-relax' ,
     restart_mode = 'from_scratch' ,
     prefix = 'cuph_3d_k444' ,
     verbosity = 'high' ,
  /
  &SYSTEM
     ibrav = 6,
     celldm(1) = 20.11677,
     celldm(3) =  2.59367,
     nat = 33,
     ntyp = 4,
     ecutwfc = 25 ,
     tot_charge = 0.000000,
     occupations = 'smearing' ,
     degauss = 0.02 ,
     smearing = 'gaussian' ,
     nspin = 2 ,
     starting_magnetization(1) = 0.0,
     starting_magnetization(2) = 0.0,
     starting_magnetization(3) = 0.0,
     starting_magnetization(4) = 0.5,
     exxdiv_treatment = 'gygi-baldereschi' ,
  /
  &ELECTRONS
  /
  &IONS
  /
  &CELL
     cell_dofree = 'xyz' ,
  /
ATOMIC_SPECIES
     N   14.00700  N.pbe-van_ak.UPF
     H    1.00800  H.pbe-van_ak.UPF
     C   12.01100  C.pbe-van_ak.UPF
    Cu   63.54600  Cu.pbe-n-van_ak.UPF
ATOMIC_POSITIONS angstrom
N       -0.002404756   1.949223697  -0.000000000
N        1.949223697  -0.002404756  -0.000000000
N        2.391389529   2.391389529   0.000000000
N        8.271536989   2.397282537  -0.000000000
N        8.695607152  -0.002619412   0.000000000
N        2.397282537   8.271536989   0.000000000
N       -0.002619412   8.695607152  -0.000000000
N        8.265225407   8.265225407   0.000000000
H        5.350243681   8.115613628   0.000000000
H        8.115613628   5.350243681   0.000000000
H        5.350427438   2.574913054   0.000000000
H        2.574913054   5.350427438   0.000000000
C        1.116474541   2.759541645   0.000000000
C        2.759541645   1.116474541  -0.000000000
C        9.548405832   2.763398467  -0.000000000
C        6.499236299   0.719922493  -0.000000000
C        7.893740728   1.123273203   0.000000000
C        5.329717857   1.479863666   0.000000000
C        4.155377490   0.720022335   0.000000000
C        2.763398467   9.548405832   0.000000000
C        0.719922493   6.499236299  -0.000000000
C        1.123273203   7.893740728   0.000000000
C        1.479863666   5.329717857  -0.000000000
C        0.720022335   4.155377490  -0.000000000
C        6.497591960   9.961479852   0.000000000
C        9.961479852   6.497591960  -0.000000000
C        7.889717032   9.542180975   0.000000000
C        9.542180975   7.889717032  -0.000000000
C        5.330043432   9.207810550   0.000000000
C        9.207810550   5.330043432  -0.000000000
C        4.156498439   9.961968783  -0.000000000
C        9.961968783   4.156498439   0.000000000
Cu      -0.017433297  -0.017433297   0.000000000
K_POINTS automatic
   4 4 4   0 0 0


Thanks in advance,
sincerely,
Dr. Yury V. Vishnevskiy
Lehrstuhl für Anorganische Chemie und Strukturchemie
Universität Bielefeld