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[Mozhgan Amini <mozhganamini@yahoo.com>]

Hi,

 

I have done the "Elastic properties" tutorial, and here is my full input file.

Thanks a lot in advance.

#PbTiO3
#Response function calculation for:
#    * rigid-atom elastic tensor
#    * rigid-atom piezoelectric tensor
#    * interatomic force constants at gamma
#    * Born effective charges

   ndtset   3

# Set 1 : Initial self-consistent run

    iscf1   5
  kptopt1   1
  tolvrs1   1.0d-18  #need excellent convergence of GS quantities for RF runs

# Set 2 : Calculate the ddk wf's - needed for piezoelectric tensor and
#         Born effective charges in dataset 3

  getwfk2  -1
    iscf2  -3        #this option is needed for ddk
  kptopt2   2        #use time-reversal symmetry only for k points
    nqpt2   1        #one wave vector will be specified
     qpt2   0 0 0    #need to specify gamma point
  rfelfd2   2        #set for ddk wf's only
   rfdir2   1 1 1    #full set of directions needed
  tolwfr2   1.0d-20  #only wf convergence can be monitored here

# Set 3 : response-function calculations for all needed perturbations

  getddk3  -1
  getwfk3  -2
    iscf3   5
  kptopt3   2        #use time-reversal symmetry only for k points
    nqpt3   1
     qpt3   0 0 0
  rfphon3   1        #do atomic displacement perturbation
 rfatpol3   1 5      #do for all atoms
  rfstrs3   3        #do strain perturbation
   rfdir3   1 1 1    #the full set of directions is needed
  tolvrs3   1.0d-10  #need reasonable convergence of 1st-order quantities

#Common input data

# acell  COPY RELAXED RESULT FROM PREVIOUS CALCULATION
# Here is a default value, for automatic testing : suppress it and fill the previous line
  acell  3*3.863 angstrom

 

  rprim   1.0  0.0  0.0   #hexagonal primitive vectors must be
          0.0  1.0  0.0   #specified with high accuracy to be
          0.0  0.0  1.0   #sure that the symmetry is recognized
                          #and preserved in the optimization
                          #process

#Definition of the atom types and atoms
 ntypat   3
  znucl   82 8 22
  natom   5
  typat   1 3 2 2 2

#Starting approximation for atomic positions in REDUCED coordinates
#based on ideal tetrahedral bond angles

# xred  COPY RELAXED RESULT FROM PREVIOUS CALCULATION
# Here is a set of default values, for automatic testing : suppress it and fill the previous line
  xred  0.0    0.0    0.0
        0.5    0.5    0.5
        0.5    0.5    0.0
        0.5    0.0    0.5
        0.0    0.5    0.5

#Gives the number of bands, explicitely (do not take the default)
  nband   13             # For an insulator (if described correctly as an
                         # insulator by DFT), conduction bands should not
                         # be included in response-function calculations

#Definition of the plane wave basis set
   ecut   45.0            # Maximum kinetic energy cutoff (Hartree)
 ecutsm   0.5            # Smoothing energy needed for lattice paramete
                         # optimization.  This will be retained for
                         # consistency throughout.

#Definition of the k-point grid
 kptopt   1              # Use symmetry and treat only inequivalent points
  ngkpt   6 6 6          # 4x4x4 Monkhorst-Pack grid
nshiftk   1              # Use one copy of grid only (default)
 shiftk   0.5 0.5 0.5    # This choice of origin for the k point grid
                         # preserves the hexagonal symmetry of the grid,
                         # which would be broken by the default choice.

#Definition of the self-consistency procedure
 diemac   6.0            # Model dielectric preconditioner
   iscf   5              # Use conjugate-gradient SCF cycle
  nstep   100            # Maxiumum number of SCF iterations


--- On Wed, 9/17/08, D. R. Hamann <drhamann@mat-simresearch.com> wrote:

From: D. R. Hamann <drhamann@mat-simresearch.com>
Subject: Re: [abinit-forum] calculation of elastic constants for PbTiO3
To: forum@abinit.org
Date: Wednesday, September 17, 2008, 5:40 AM

Dear mozhganamini,

Your input file does not look like an elastic-constants input file.  
Have you done the "Elastic properties" tutorial?  Without the full
input 
file that gave these results, it is hard to diagnose your problem.  I 
see no "tol..." input variables, and the convergence criteria to get 
good elastic constant (and other response function) results are much 
tighter than the defaults that your attached ground-state file 
apparently would get.

Don Hamann

mozhganamini@yahoo.com wrote:
> Dear all,
> I'm trying to calculate the elastic constants of PbTiO3 for comparing
the
> results with:  " Y. Liu et al. , Materials Science and Engineering A
472(2008)
> "
> but my results are approximately twice the results in this article!?
> Thanks a lot in advance
>
> my results for elastic		  results in article
> C11: 629 (GPa)				     383
> C12: 192					 151 
> C44: 116					 120
>
> my input file:
>
>  acell	3*3.863 angstrom
>  rprim 1.0  0.0  0.0 
> 	   0.0	1.0  0.0   
> 	   0.0	0.0  1.0	  
> #Definition of the atom types and atoms
>  ntypat   3 
>  znucl	 82 8 22
>  natom	 5
>  typat	 1 3 2 2 2
>
>   xred	0.0    0.0    0.0
> 	0.5    0.5    0.5
> 	0.5    0.5    0.0
> 	0.5    0.0    0.5
> 	0.0    0.5    0.5
>
>  nband	 13	 
> 	      
> #Definition of the plane wave basis set
>    ecut   45.0	 
>  ecutsm   0.5	     
> 			 
> #Definition of the k-point grid
>  kptopt   1	     
> ngkpt	6 6 6	
> nshiftk   1	       
>  shiftk   0.5 0.5 0.5	
> 	   
> #Definition of the self-consistency procedure
>  diemac   6.0	 
>    iscf   5		
>   nstep   100	      
>
>   

-- 
D. R. Hamann
Mat-Sim Research LLC    | Deptartment of Physics
P.O. Box 742            |  and Astronomy
Murray Hill, NJ 07974   | Rutgers University
phone: 908-370-8079     | 732-445-4381

email: drhamann@mat-simresearch.com