The ABINIT Users Mailing List ( CLOSED )

[Katalin Gaal-Nagy <katalin.gaal-nagy@physik.uni-regensburg.de>]

Dear Javier,

imaginary frequencies can have various reasons (I am sorry, I didn't check 
your input files because of a lack of time):
- numerical instability (not converged enough with respect to k, ecut,
  etc)
- the structure is instable, meaninig:
  There exist a structure in the same cell, maybe with less symmetry,
  which has a lower energy as the same volume and is therefor more stable.
  What happens with your cell if you don't put any symmetry?

Maybe it helps ...

Katalin


On Fri, 9 Jun 2006, Javier Torres wrote:

> Dear Anglade
>
> Thank you for the interest...
>
> When I say special positions for the atoms I mean that they can not be 
> relaxed during the optimization, their fractional coordinates are fixed and 
> the interatomic distance changes when they are scaled with the new lattice 
> parameters... As result of that the forces become smaller too as I could see 
> in the output of the optimization...
>
> cartesian coordinates (angstrom) at end:
>   1      0.00000000000000     0.00000000000000     0.00000000000000
>   2      0.00000000000000     1.72195994003625     2.00945363615211
>   3      1.49126105237052     0.86097997001812     2.00945363615211
>
> cartesian forces (hartree/bohr) at end:    1      0.00000000000000 
> 0.00000000000000     0.00000000000000
>   2      0.00000000000000     0.00000000000000     0.00000000000000
>   3      0.00000000000000     0.00000000000000     0.00000000000000
> frms,max,avg= 5.3532090E-31 9.8765995E-31   0.000E+00  0.000E+00  0.000E+00 
> h/b
>
> cartesian forces (eV/Angstrom) at end:
>   1      0.00000000000000     0.00000000000000     0.00000000000000
>   2      0.00000000000000     0.00000000000000     0.00000000000000
>   3      0.00000000000000     0.00000000000000     0.00000000000000
> frms,max,avg= 2.7527306E-29 5.0787513E-29   0.000E+00  0.000E+00  0.000E+00 
> e/A
>
> What else can produce wrong freqs????
>
> Kind regards----
>
> FT