The ABINIT Users Mailing List ( CLOSED )

[marek.veithen@ulg.ac.be]

Dear users of ABINIT

I had recently some trouble with the structural optimization
of Wurzite type II-VI semiconductors. The BFGS algorithm(ionmov 2 or 3)
was not able to converge the forces on the atoms and the stresses
on the unit cell to the imposed tolerance criterium.

To overcome this problem, I modified the initialization of the inverse
hessian that is done in the routine Src_9drive/brdmin.f.

  if(optcell/=0)then
!  These values might lead to too large changes in some cases ...
   diag=30.0d0/ucvol
   if(optcell==1)diag=diag/3.0d0
   do idim=3*natom+1,ndim
    hessin(idim,idim)=diag
   enddo
  endif
  write(message, '(a)' )' Inverse hessian has been initialized.'
  call wrtout(06,message,'COLL')
 endif

By imposing a smaller value of diag, I was able to converge the
forces on the atoms and the stresses on the unit cell down to 5.0d-5 and
5.0d-7 respectively usigng typically between 10 and 30 Broyden steps.

In case other people have similar difficulties with structural optimizations
it could be useful to know how they handle to overcome these problems in
order to improve the efficiency of the BFGS algorithm.