The ABINIT Users Mailing List ( CLOSED )

[Hua Bao <hbao@purdue.edu>]

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
> >
> >
> >
> >
> >     
>
>
>