151
General Questions and Answers / Re: Ph.-DOS /transmission eigen values
« on: July 7, 2015, 09:12 »
For the Stillinger-Weber and Tersoff-potentials the default values usually work well. You don't need to specify the maximum interaction range in the DynamicalMatrix parameters.
In your case, I'd rather suspect that there is something odd with the structure. Negative frequencies mean that there are soft modes present in the system, either by atoms sitting in a local saddle point.
You could try to calculate the phonon bandstructure (without checking Accoustic sum rule and Symmetrize) and then the location of the negative frequencies might give you some hints. If the negative frequencies occur at gamma, then you might need to increase the maximum interaction range, if the negative frequencies occur elsewhere, then it is likely that your structure is not in a local minimum.
In your case, I'd rather suspect that there is something odd with the structure. Negative frequencies mean that there are soft modes present in the system, either by atoms sitting in a local saddle point.
You could try to calculate the phonon bandstructure (without checking Accoustic sum rule and Symmetrize) and then the location of the negative frequencies might give you some hints. If the negative frequencies occur at gamma, then you might need to increase the maximum interaction range, if the negative frequencies occur elsewhere, then it is likely that your structure is not in a local minimum.