[Pw_forum] Convergence problem with Ni/Ni3Al system

[elbuesta at icqmail.com]

Dear Adriano Martins, 

if the SCF calculation is not converging, than you should reduce the mixing_beta parameter. I never performed calculations on your specific system, but for the Ni-X surfaces that I've studied I had to use a mixing_beta should equal to 0.05-0.4 in order to reach convergence.

I hope it helps,

Fabio Negreiros Ribeiro
IPCF - CNR
Pisa, Italy

-----Original Message-----

From: martins <martins at if.uff.br>
To: pw_forum <pw_forum at pwscf.org>
Sent: Tue, Sep 13, 2011 9:28 pm
Subject: [Pw_forum] Convergence problem with Ni/Ni3Al system


Dear all,

I'm studying the Ni/Ni3Al system. In order to estimate the value of  
the interface energy, I built several supercells keeping Nx = Ny = 1  
(the Ni and Ni3Al lattice parameters are commensurated) and vary the  
number of unitary cells along the z direction, but constraining the  
numbers of Ni and Ni3Al cells to be equal. For small systems, nz = 2  
and nz = 4, the calculations runned without any problem. However, for  
nz = 6 and nz = 8 I'm having problems of convergency: the quantum  
espresso is unable to reach the minimum value of energy. I tried  
several modifications:

i) Increase ecutwfc and the k-point sampling;

ii) Increase ecutrho;

iii) Modify the ion and cell dynamics options;

iv) ...

Bellow I send the input file. I appeciate any help to solve this  
problem. If someone want to write me directly to my personal e-mail,  
fell free! One last information: I tried too to run only a SCF  
calculation... and the result not converged.

Thanks in advance,

Adriano Martins (Universidade Federal Fluminense - Brazil)

-------------------- Typical Input File -------------------------------
&control
     calculation = 'vc-relax',
     restart_mode='from_scratch'
     prefix='NiNi3Al'
     tstress = .true.
     tprnfor = .true.
     pseudo_dir = '/home/martins/programas/espresso-4.3.2/pseudo/',
     outdir='/home/martins/calculos/QE/NiNi3Al/nx1ny1nz6/'
  /
  &system
       ibrav =  0,
   celldm(1) = 40.35,
         nat =  24,
        ntyp = 2,
     ecutwfc = 40.0,
     ecutrho = 320,
       nspin = 2,
starting_magnetization(1) = 0.0,
starting_magnetization(2) = 0.2,
occupations = 'smearing',
    smearing = 'gaussian',
     degauss = 0.02,
  /
  &electrons
     diagonalization='david'
     mixing_mode = 'plain'
     mixing_beta = 0.70
     conv_thr =  1.0d-6
  /
&ions
ion_dynamics = 'bfgs'
/
&cell
cell_dynamics = 'bfgs'
   cell_dofree = 'z'
/
CELL_PARAMETERS
      0.16667     0.00000     0.00000
      0.00000     0.16667     0.00000
      0.00000     0.00000     1.00000
ATOMIC_SPECIES
  Al  26.981  Al.pbe-sp-van.UPF
  Ni  58.693  Ni.pbe-nd-rrkjus.UPF
ATOMIC_POSITIONS  alat
Ni     0.00000     0.00000     0.00000
Ni     0.00000     0.08333     0.08333
Ni     0.08333     0.08333     0.00000
Ni     0.08333     0.00000     0.08333
Ni     0.00000     0.00000     0.16667
Ni     0.00000     0.08333     0.25000
Ni     0.08333     0.08333     0.16667
Ni     0.08333     0.00000     0.25000
Ni     0.00000     0.00000     0.33333
Ni     0.00000     0.08333     0.41667
Ni     0.08333     0.08333     0.33333
Ni     0.08333     0.00000     0.41667
Al     0.00000     0.00000     0.50000
Ni     0.00000     0.08333     0.58333
Ni     0.08333     0.08333     0.50000
Ni     0.08333     0.00000     0.58333
Al     0.00000     0.00000     0.66667
Ni     0.00000     0.08333     0.75000
Ni     0.08333     0.08333     0.66667
Ni     0.08333     0.00000     0.75000
Al     0.00000     0.00000     0.83333
Ni     0.00000     0.08333     0.91667
Ni     0.08333     0.08333     0.83333
Ni     0.08333     0.00000     0.91667
K_POINTS automatic
  8  8  2  1  1  1


----------------------------------------------------------------------


------------------------------------
Adriano de Souza Martins
Professor Adjunto III
Departamento de Física - ICEx
Polo Universitário de Volta Redonda
Universidade Federal Fluminense
------------------------------------

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