The ABINIT Users Mailing List ( CLOSED )

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

As a user, you can just guess those parameters  from the input
variables informations. You could also read the literature,
unfortunately the articles about the preconditioning are not yet
published. One day or another one may write a tutorial on
preconditioning.
Anyway you need very few knowledge about preconditioners to use them:
a) If you have a homogeneous system you can set diemac to the
macroscopic permittivity of your materials
b) If your system is smaller than 100-1000 atoms and is not
homogeneous, always use iprcel 4x.
c) If your system is smaller than 100-1000 atoms  and converges slowly
use iprcel 4x or even 6x
The preconditioning is not something very complicate to this respect.

You may want to give a look at this document:
http://anglade.googlepages.com/anglade-preconditioners.pdf
which elaborate on what you have already read in the reference I have
given to you previously.

regards

PMA


On 8/29/07, Hua Bao <hbao@purdue.edu> wrote:
> Dear Anglade Pierre-Matthieu,
>
> I will try that.
>
> BTW, as a user, is there any efficient way to learn to choose those
> parameters myself ? Is it just an accumulation of experience? Do I need
> to dig into the algorithm?
>
> Thanks,
> Hua
>
>
> Anglade Pierre-Matthieu wrote:
> > using kerker's preconditioner is not efficient in your case since you
> > consider a cluster. So forget about diemac. Instead use
> > iprcel 4x
> > diecut 1
> >
> > The best is to tune the x in 4x so that it is the number of the last
> > converging step. For instance
> > if you try 49 and get
> > ETOT1 -407 -407
> > ETOT2 -408    -1
> > ETOT3 -409    -1
> > ETOT4 -408   +1
> > ...
> >
> > You'd better try "iprcel 43".
> > With this you should achieve perfect convergency in less than 50 steps.
> > If this fails I recommand that you try "iprcel 14x". (with your
> > previously determined x).
> > You should get the required level of convergency in probably less than
> > 20 steps eventhough they cost much more you'll win a lot of your time.
> > Notice however that the computation associated with iprcel are not
> > parallelized over band... sorry
> >
> > PMA
> >
> >
> > On 8/29/07, Hua Bao <hbao@purdue.edu> wrote:
> >
> >> Dear Anglade Pierre-Matthieu,
> >>
> >> Thank you for your fast reply. I am using infinite band, so I guess
> >> parallel may help a little.
> >> I am using MT type norm-conserving pseudopotential for both Ti and O
> >> (22ti.pspnc and 8o.pspnc).
> >>
> >> Below is my input file and part of the output,
> >> 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    7
> >> npulayit 20
> >> chkprim 1
> >> toldff  1.0d-4
> >> xangst 9.186000    9.186000   11.779326
> >> 10.506552   10.505191   12.167015
> >> 7.865448    7.866809   12.167015
> >> 9.186000    9.186000    8.877000
> >> .........
> >> #Definition of the unit cell
> >> acell  15 15 15  angstrom
> >> angdeg 90 90 90
> >> ntypat 2
> >> znucl 22 8
> >> 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
> >> ecut 30.0         # Maximal kinetic energy cut-off, in Hartree
> >> #Definition of the k-point grid
> >> nkpt 1
> >>
> >> nstep 500          # Maximal number of SCF cycles
> >> diemac 50
> >>
> >> Output,
> >> .....
> >>  Symmetries : space group P1 (#  1); Bravais aP (primitive triclinic)
> >> ================================================================================
> >>  Values of the parameters that define the memory need of the present run
> >>    intxc =         0  ionmov =         3    iscf =         7     ixc
> >> =         1
> >>   lmnmax =         2   lnmax =         2   mband =        93  mffmem
> >> =         1
> >> P  mgfft =       144   mkmem =         1 mpssoang=         3     mpw
> >> =     89463
> >>   mqgrid =      3001   natom =        33    nfft =   2985984    nkpt
> >> =         1
> >>   nloalg =         4  nspden =         1 nspinor =         1  nsppol
> >> =         1
> >>     nsym =         1  n1xccc =      2501  ntypat =         2  occopt
> >> =         1
> >> ================================================================================
> >> .....
> >>  ETOT  1  -390.60418925724    -3.906E+02 1.162E-01 2.003E+05 6.522E-01
> >> 6.522E-01
> >>  ETOT  2  -399.15192426392    -8.548E+00 1.729E-01 9.015E+04 1.048E+00
> >> 6.410E-01
> >>  ETOT  3  -407.53310732403    -8.381E+00 4.573E-02 4.745E+04 7.852E-01
> >> 4.791E-01
> >>  ETOT  4  -407.92518738003    -3.921E-01 3.082E-02 3.906E+04 1.451E-01
> >> 4.030E-01
> >>  ETOT  5  -405.54214107012     2.383E+00 1.644E-02 7.648E+04 6.195E-01
> >> 5.258E-01
> >>  ETOT  6  -408.24685027392    -2.705E+00 1.358E-02 2.997E+04 6.768E-01
> >> 3.641E-01
> >> ......
> >>  ETOT 50  -409.77792273642    -8.557E-03 2.940E-05 1.482E+03 4.318E-02
> >> 9.077E-02
> >>  ETOT 51  -409.78097373049    -3.051E-03 1.125E-05 2.254E+03 7.028E-02
> >> 1.043E-01
> >>  ETOT 52  -409.84803111241    -6.706E-02 2.862E-05 2.478E+02 5.466E-02
> >> 6.845E-02
> >>  ETOT 53  -409.79189318401     5.614E-02 1.107E-05 2.079E+03 6.247E-02
> >> 9.658E-02
> >>  ETOT 54  -409.82779081084    -3.590E-02 2.751E-05 6.042E+02 6.102E-02
> >> 8.605E-02
> >>  ETOT 55  -409.78546959552     4.232E-02 1.143E-05 1.367E+03 3.418E-02
> >> 9.129E-02
> >>  ETOT 56  -409.83178716613    -4.632E-02 2.502E-05 4.860E+02 7.159E-02
> >> 9.624E-02
> >> .........
> >>  ETOT261  -409.86217751005     7.211E-04 4.555E-08 8.010E+01 6.128E-03
> >> 7.429E-02
> >>  ETOT262  -409.86060355976     1.574E-03 7.512E-08 1.062E+02 5.525E-03
> >> 7.759E-02
> >>  ETOT263  -409.86285205630    -2.248E-03 4.087E-08 6.501E+01 7.248E-03
> >> 7.305E-02
> >>  ETOT264  -409.85658369085     6.268E-03 6.611E-08 1.735E+02 1.226E-02
> >> 7.614E-02
> >>  ETOT265  -409.86055804058    -3.974E-03 3.425E-08 1.007E+02 5.539E-03
> >> 7.763E-02
> >>  ETOT266  -409.86273053407    -2.172E-03 6.215E-08 7.162E+01 1.099E-02
> >> 7.444E-02
> >>  ETOT267  -409.84672451979     1.601E-02 4.149E-08 2.413E+02 2.870E-02
> >> 5.157E-02
> >>  ETOT268  -409.85874398923    -1.202E-02 5.906E-08 1.028E+02 1.905E-02
> >> 6.155E-02
> >>  ETOT269  -409.85148059726     7.263E-03 3.656E-08 2.451E+02 2.618E-02
> >> 7.902E-02
> >> Anglade Pierre-Matthieu wrote:
> >>
> >>> Hi,
> >>>
> >>> OK, it looks like your system is a difficult one. Please send the
> >>> various input and relevant part of the output so that we can give you
> >>> a better diagnose (just the change with respect to the first one you
> >>> send will be sufficient). I'm quite astonished that you do not get
> >>> perfect convergency following my previous advices. Is it possible that
> >>> you did a mistake ? Or are you using PAW ?
> >>>
> >>> About parallel computing:
> >>> - If you use a single k-point, you must rely on the band FFT. It
> >>> requires a fast network. Forget about it if you use ethernet.
> >>> -If you have a few k-point use as much processor as k-point .
> >>> Parallelism will decrease the time per step. But never enhance the
> >>> convergence you get.
> >>>
> >>> Regards
> >>>
> >>> PMA
> >>> O
> >>>
> >>
> >
> >
> >
>
>


-- 
Pierre-Matthieu Anglade