The ABINIT Users Mailing List ( CLOSED )

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

Don't worry too much for positive deltaE as long ad you get some signs
of convergence in less than "npulayit" steps.
If you really require a steady convergence you can just use:
iprcel 141
The computation will converge steadily but every step will last twice
as long as before.

On 8/28/07, Hua Bao <hbao@purdue.edu> wrote:
> Dear Anglade and all,
>
> Thank you for your suggestion.
> Here I've got some positive deltaE while doing SCF calculation (using
> iscf 5 or 7) . I know this happens. How to deal with it? It seems it
> will fluctuating for ever?
>
> Thanks,
> Hua
>
>
>
>
> Anglade Pierre-Matthieu wrote:
> > 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