[Pw_forum] RE : Re: how to optimize the lattice parameters of monoclinic structure ?

[Fatma Litimein]

  Dear Javad,
  Thank you very much for your help, and for your time.
  I have already done the vc relaxation. The problem is in my output file.The crystal axes seems to be not similar to that in  INPUT_PW file.
  Any comments are highly appreciated. 
  Regards,
  Fatma
  
  monoclinic (p)
   
  ====================== INPUT_PW ======================
    v1 = (a,0,0), v2= (b*cos(gamma), b*sin(gamma), 0),  v3 = (0, 0, c)
                  where gamma is the angle between axis a and b
  ============here is my output file=================
    bravais-lattice index = 12
  lattice parameter (a_0) = 23.1113 a.u.
  unit-cell volume = 1413.2148 (a.u.)^3
  number of atoms/cell = 20
  number of atomic types = 5
  number of electrons = 176.00
  number of Kohn-Sham states= 88
  kinetic-energy cutoff = 25.0000 Ry
  charge density cutoff = 100.0000 Ry
  convergence threshold = 1.0E-08
  mixing beta = 0.7000
  number of iterations used = 8 plain mixing
  Exchange-correlation = SLA PW GGX GGC (1422)
  nstep = 55
   
  celldm(1)= 23.111300 celldm(2)= 0.248500 celldm(3)= 0.474200
  celldm(4)= -0.237000 celldm(5)= 0.000000 celldm(6)= 0.000000
   
  crystal axes: (cart. coord. in units of a_0)
  a(1) = ( 1.000000 0.000000 0.000000 ) 
  a(2) = ( -0.058895 0.241420 0.000000 ) 
  a(3) = ( 0.000000 0.000000 0.474200 ) 
   
  reciprocal axes: (cart. coord. in units 2 pi/a_0)
  b(1) = ( 1.000000 0.243950 -0.000000 ) 
  b(2) = ( 0.000000 4.142156 0.000000 ) 
  b(3) = ( 0.000000 -0.000000 2.108815 ) 
   
  :
  .
  :
   
  No symmetry!

   
  .
  .
  .
  ==========================================================
  
 
  
Javad hashemifar <jhashemifar at gmail.com> a écrit :
    Dear Fatma
  I think the best option for you is the vc (volume-cell) relaxation. In this kind of calculations all lattice parameters and atomic positions are relaxed simultaneously. Please see the INPUT_PW file for adjusting the required input parameters.
  another option is to relax lattice parameters one by one. In each step you should vary one lattice parameter and fix others. After finding the optimized value of this lattice parameter, it should be fixed and another lattice parameter should be optimized. The following sequence of relaxation may be useful:
   
  1. betha (a, b/a, and c/a are fixed to experimental or any other reported value)
  2. Volume (betha, b/a, and c/a should be fixed)
  3. b/a (betha, Volume, and c/a are fixed)
  4. c/a (bethe, Volume, and b/a are fixed)
   
  it is better to repeat the above sequence more than one time.
   
  It should be noted that vc relaxation seems to be more appropriate for you.
   
  Javad
  

 
  On Mon, Jul 7, 2008 at 10:52 PM, Fatma Litimein <flitimein at yahoo.fr> wrote:
      
    Dear PWscf users,       I have a question about optimization of an monoclinic  structure, so to do that have I to optimize c/a, V, b/a, V, ...., beta, V,  in SCF manner until convergence of the structure or can I  perform just one c/a, b/a, V optimization ? How can I to optimize i.e. beta angel? Any comments are welcome. 
  Thank you in advance 






=======================================================
Fatma Litimein 
Computational Materials Science Laboratory,
Physics Department, University of Sidi Bel Abbes
Sidi Bel Abbes, 22000 - Algeria
Tel:+213 48-54-95-46 Fax:+213 48-54-19-28 flitimein at yahoo.fr
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-- 
======================================
Seyed Javad Hashemifar, Ph.D.
current address:
Physics Department, University of Duisburg-Essen, 
47057 Duisburg, Germany
Tel:+49 203 379 4743 Fax:+49 203 379 4741
permanent address:
Physics Department, Isfahan University of Technology
84154 Isfahan, Iran
Tel: +98 311 391 2375 Fax:+98 311 3912376
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=======================================================
Fatma Litimein 
Computational Materials Science Laboratory,
Physics Department, University of Sidi Bel Abbes
Sidi Bel Abbes, 22000 - Algeria
Tel:+213 48-54-95-46 Fax:+213 48-54-19-28 flitimein at yahoo.fr
=======================================================
       
---------------------------------
 Envoyé avec Yahoo! Mail.
Une boite mail plus intelligente. 
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