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[okuno@osa.sci.jri.co.jp]

Dear Abinit Users.

I'm now trying to optimize the atom positions 
of the LaGaO_{3} whose  space group is Pnma and contains 
20 atoms in the unit cell.

I'm use abinit input option 
ionmov=2 and ntimes=100 but the results are 
not conversed. 

Abinit outputs WARNING like..

fconv : WARNING -
  ntime=  100 was not enough Broyd/MD steps to converge gradients:
  max grad (force/stress) = 2.2787E-04 > tolmxf= 5.0000E-05 ha/bohr (free 
atoms\
)

the results (max gfad(force/stress)) seems ossilate and not easy to 
conversed. 

Another try we take is to use molecular dynamics with damping factor that 
is 

ionmov=1, vis=400, dtion 200.0 and ntime= 500 and =1000.

But the result seems that the atoms are moving with time and not converse
to stable positions. 
Are there some techniques that optimize the atom positions in rather large 
cell? 

Some body know the ideas to optimize atom positions such system, 
it is my pleasure to teach me.

Sincealy.

Yukihiro Okuno

My input file for optimization is like below
#____ Here begins abinit input file 

#ndtset 2

ionmov 2
ntime  200
#vis 400.0
#dtion 200.0
#ntime1 500.
#ntome2 1000




#Definition of the unit cell
acell  10.365147  14.683171 10.436957
rprim  1.0  0.0  0.0
       0.0  1.0  0.0
       0.0  0.0  1.0

#Definition of the atom types
ntype 3
znucl 57 31 8  # for La, Ga, O
#Definition of the atoms
natom 20
type 2 2 2 2 1 1 1 1 3 3 3 3 3 3 3 3 3 3 3 3
xred
    0.00000   0.0       0.5
    0.50000   0.5       0.0
    0.00000   0.5       0.5
    0.50000   0.0       0.0
   -0.009900  0.250    -0.002900
    0.490100  0.250     0.502900
    0.009900  0.750     0.002900
    0.509900  0.750     0.497100
    0.498000  0.250     0.060000
    0.998000  0.250     0.440000
   -0.498000  0.750    -0.060000
    0.002000  0.750     0.560000
    0.229000  0.037000  0.762000
    0.729000  0.463000 -0.262000
   -0.229000  0.537000 -0.762000
    0.271000 -0.037000  1.262000
   -0.229000 -0.037000 -0.762000
    0.271000  0.537000  1.262000
    0.229000  0.463000  0.762000
    0.729000  0.037000 -0.262000

#Definition of the planewave basis set
#ecut1  40.0         # Maximal kinetic energy cut-off, in Hartree
ecut  35.0
#Definition of the k-point grid
kptopt 1
ngkpt 4 4 4

#Definition of the SCF procedure
nstep  100          # Maximal number of SCF cycles
toldfe 1.0d-6     # Will stop when, twice in a row, the difference
                  # between two consecutive evaluations of total energy
                  # differ by less than toldfe (in Hartree)
diemac 12.0       # Although this is not mandatory, it is worth to
                  # precondition the SCF cycle. The model dielectric
                  # function used as the standard preconditioner
                  # is described in the "dielng" input variable section.
                  # Here, we follow the prescription for bulk silicon.