[Pw_forum] Cell optimization converges to unrealistic value

Giuseppe Mattioli giuseppe.mattioli at ism.cnr.it
Fri Oct 12 12:53:26 CEST 2012


Dear Yuri
I'm not sure whether my previous answer to your previous post (identical to this one... Do not ask 
two times the same question, please) reached the forum, thus I paste it below, with some corrections 
wrt the previous version.

There are several technical and physical reasons behind your unrealistic results.

Technical:

>      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

>      ecutwfc = 25 ,

In the case of ultrasoft pseudopotential, ecutrho has to be indicated, having a value between 
6*ecutwfc and 10*ecutwfc (convergence should be reached with respect to all such values, but I 
perform satisfactorily converged CuPc calculations with the same pseudos by using 
ecutwfc=35/ecutrho=280 cutoffs...)

>      tot_charge = 0.000000,
>      starting_magnetization(1) = 0.0,
>      starting_magnetization(2) = 0.0,
>      starting_magnetization(3) = 0.0,
>      exxdiv_treatment = 'gygi-baldereschi' ,

useless keywords (in this case...). Starting_magnetization(4) = x with 0.0 < x < 1.0 is enough to 
break the spin symmetry.

>      nat = 33,

The copper phthalocyanine (CuPc) has 57 atoms. Your system is a sort of periodical "graphene-like" 
sheet, or "graphite-like" crystal, based on CuPc.

>      ibrav = 6,
>      celldm(1) = 20.11677,
>      celldm(3) =  2.59367,

your sheet is embedded into a tetragonal cell, and it seems to be placed at a z distance of about 30 
A from its periodically repeated image... Check the exact use of the celldm(i) variables: 2.59367 
means that the c parameter is 2.59367*20.11677 a.u.

Physical:

Molecular crystals or layered molecular structures stay together because of dispersion interactions. 
As you are not using any kind of dispersion correction, you will never obtain meaningful results on 
lattice parameters. There is plenty of theoretical papers investigating the CuPc molecule, or the 
graphite packing. I suggest you to start with them...

HTH

Giuseppe

On Friday 12 October 2012 12:18:22 Yury Vishnevskiy wrote:
> 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
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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
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