The ABINIT Users Mailing List ( CLOSED )

["Anglade Pierre-Matthieu" <anglade@gmail.com>]

Hi,

To get faster convergence within Abinit you can use:
1) better mixing algorithm like pulay:
iscf 7
npulayit 20

2) preconditionners
a) try
iprcel 45
(& diecut 1  if you feel preconditionning is too long).
It's based on KM Ho preconditioner (prb 25 4260 1982)  and is very efficient
b) also you can just tune the default preconditioner based on Kerker's
method (PRB 23 3082 1981)
by setting more accurate value for diemac (try something around diemac 50).

3) Also make sure you get both convergence for the potential (vres2)
and for the wave functions (residm). With the suggested change you'll
get a very good convergence of the first one and it is likely that you
need to increase "nline" to get the other.

regards

PMA

On 8/28/07, Hua Bao <hbao@purdue.edu> wrote:
> Dear all,
>
> First, I have a general question. How to get a faster SCF
> calculation? I appreciate if you can point out which literatures to
> refer.
>
> I am doing a geometry optimization of TiO2 cluster contains less than
> 40 atoms. The SCF calculation is really slow. It take a few hundreds
> steps to get convergent. The energy sometimes is fluctuating. So I
> expect it would take a really long time to achieve geometry
> optimization. Parallel running does not help too much, either. Since
> my initial geometry is a little far from optimization. Is there any
> faster way to get a optimized structure?
>
> Here is my input file, NCpp is used.
>
> ionmov  3              # Use the modified Broyden algorithm
> ntime   1000             # Maximum number of Broyden "timesteps"
> tolmxf  1.0d-4         # Stopping criterion for the geometry
> optimization : when
> iscf    5
> chkprim 1
>
> toldff  1.0d-4         # Will stop the SCF cycle when, twice in a row,
>                         # the difference between two consecutive
> evaluations of
>                         # forces differ by less than toldff (in
> Hartree/Bohr)
>
>
> xangst   9.186000    9.186000   11.779326
> .......
> acell  15 15 15  angstrom  # The keyword "acell" refers to the
> angdeg 90 90 90
>
> ntypat 2          #
> znucl 22 8      # The keyword "znucl" refers to the atomic number of the
>
>
> #Definition of the atoms
> natom 33
> typat 1 2 2 1 2 1 2 2 2 1 2 2 2 1 2 2 1 2 2 2 1 2 1 2 2 1 2 1 2 1 2 2 2
>
> #Definition of the planewave basis set
> ecut 30.0         # Maximal kinetic energy cut-off, in Hartree
>
> #Definition of the k-point grid
> nkpt 1
> #Definition of the SCF procedure
> nstep 500          # Maximal number of SCF cycles
>
>
> Thanks,
>
> Hua Bao
> Graduate Student
> School of Mechanical Engineering,
> Purdue University
> O: 765-494-6944
>
>
>
>


-- 
Pierre-Matthieu Anglade