Dear all, I am trying to check the stability of a 1D sulfur chain. However I am getting weird dispersion branches (see attached figure with 11 q-grid point). this remains even with a denser q grid.
The K grid is well converged and ecutwfc was chosen to be 100Ry A.so tr2_ph is set to 10^(-20). I even tried different pseudopotentials. This doesnt happen if Aluminium 1D chains were considered. The phonon branches at the k points in the phonon grids (uisng ph.x) all have poistive frequencies. However the interpolation using matdyn.x becomes problematic and produces very large negative frequencies. Any idea what is going on? Thanks in advance Elio University of Rondonia Brazil
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