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[mmikami@rc.m-kagaku.co.jp]

Hi,

More exactly speaking, the nband should be set to the number of valence 
bands, which depend on the valences of the pseudopotentials.

The input files attached in the original post (thanks to follow our 
Netiquette), he wants to compute Sr2MgSi2O7. (It would have been mentioned 
clearly in the original post...) The unit cell contains two formula, which 
lead to "natom 24".

If one treats the valence of Sr as two, nband should be
(2*2 + 2 + 4*2 + 6*7)*2/2 = 56,
but if one treats the valence of Sr as ten (i.e. shallow core s/p states 
included as valence), as often in oxides, nband should be 
(10*2 + 2 + 4*2 + 6*7)*2/2 = 72.
In this case, the ecut should be determined by the hardness of Sr pseudo 
rather than O pseudo. "ecut 40" might be barely OK, but higher ecut may be 
preferred for RF calculations. 
(Please check by yourself !)

Good luck,
Masayoshi

P.S. "=" should be removed in the input file, e.g., "chkprim=0", "brvltt=0". 

From: "Yanqing Zheng" <yqzheng1@sh163.net>
To: "forum@abinit.org" <forum@abinit.org>
Reply-To: forum@abinit.org
Subject: Re: [abinit-forum] convergence problen in RF calculation
Date: Sun, 16 Apr 2006 00:28:54 +0800
X-mailer: Foxmail 5.0 [cn]

Dear Zeming,
Set nband to be 56.
Wish it help.

Good luck!

Yanqing Zheng, Ph.D.
Shanghai Institute of Ceramics,
Chinese Academy of Sciences
Jiading, 201800, Shanghai
P. R. China
E-mail: yqzheng@sh163.net
Fax no.: +86 21 59927184

Dear all, 
   I am trying the Response-function calculation of the effect of an 
homogeneous electric field.  For the first step GS calculation, it is easy to 
reach tolvrs=  1.00E-18 and converged. But, for the second step, a 
non-self-consistent response-function computation of the d/dk perturbation, 
it seems that it is very difficult to converge. After 70 steps, the maximum 
residual only reached about 2E-04 (>>tolwfr= 1.0E-22) and oscillated around 
this value. The tutorial and help of Abinit said it should be use a very 
small tolwfr value. So, I'd like to know how to select a suitable tolwfr for 
different system in RF calcualtion and what input variables influence the 
convergence mostly. Anyone have any suggestion to speed convergence? Thanks 
in advance.

regards,
Zeming
---------------------------
The input file is as follows.
#Response-function calculation, with q=0

  ndtset  3

#Ground state calculation
  kptopt1   1             # Automatic generation of k points, taking
                          # into account the symmetry
  tolvrs1   1.0d-18       # SCF stopping criterion
    iscf1   5             # Self-consistent calculation, using algorithm 5

#Response Function calculation : d/dk
  rfelfd2   2             # Activate the calculation of the d/dk perturbation
   rfdir2   1 1 1                                
    nqpt2   1
     qpt2   0.0 0.0 0.0   # This is a calculation at the Gamma point

  getwfk2   -1            # Uses as input the output wf of the previous 
dataset

  kptopt2   2             # Automatic generation of k points,
                          # using only the time-reversal symmetry to decrease
                          # the size of the k point set.

    iscf2  -3             # The d/dk perturbation must be treated 
                          # in a non-self-consistent way
  tolwfr2   1.0d-22      # Must use tolwfr for non-self-consistent 
calculations
                          

#Response Function calculation : electric field perturbation and phonons
  rfphon3   1        #the calculation of the atomic dispacement perturbations
 rfatpol3   1 24           # All the atoms will be displaced
  rfelfd3   3            
  rfdir3   1 1 1         # All directions                       
  nqpt3   1
  qpt3   0.0 0.0 0.0   # This is a calculation at the Gamma point
  getwfk3   -2            # Uses as input wfs the output wfs of the dataset 1
  getddk3   -1            # Uses as input ddk wfs the output of the dataset 2

  kptopt3   2             # Automatic generation of k points,
                          # using only the time-reversal symmetry to decrease
                          # the size of the k point set.
  tolvrs3   1.0d-8
    iscf3   5             # Self-consistent calculation, using algorithm 5 



#Definition of the unit cell
acell 15.09060  15.09060  9.76535        # This is lattice constant
angdeg 90 90 90

#Definition of the atom types
ntypat 4          
znucl 38 12 14 8   
                                                  
                         
#Definition of the atoms
spgroup 113 #  P-421m
chkprim=0

natom 24 
brvltt=0
natrd 6
nband 80

typat 1 2 3 4 4 4   
xred                                
0.33869   0.16131   0.50958 
0.00000   0.00000   0.00000 
0.13924   0.36076   0.95060 
0.50000   0.00000   0.14329 
0.14160   0.35840   0.25931 
0.07613   0.19200   0.80587 
      
ecut 40  # Maximal kinetic energy cut-off, in Hartree


#Definition of the k-point grid

ngkpt  4 4 4
nshiftk 1         # of the reciprocal space (that form a BCC lattice !),
shiftk 0.50 0.50 0.50

#Definition of the SCF procedure
nstep 70          # Maximal number of SCF cycles
diemac 2.0