Dear Li Yan, I was checking my very old work today (it was my diploma work, I am sorry, it is not published and it is in German), and the final solution of my former problem with my numerical instability was an increase of the k-points of the Ground state together with an increase of the number of q-points for the phonons. On Monday I can send you some figures. It was not enough just to increase the number of q-points.
Have a nice weekend, best wishes, Katalin > Dear katalin, > > I want to find the reason of the phase transiton for AgF by > calculating the phonon dispersion curves. My intent is finding the soft > mode at high pressure. > > >Which was the first grid, which you used to calculate the dispersion? > > AgF is fcc strcture, c/a is 1, so the mesh was initially chosen as > 4*4*4. > > At 3GPa, after calculating the eight special points, i found only one > of them (0,0,1) has a negative mode. Then i did the calculation of > the phonon disperion curves with q2r.x, the frequences of TA near the > gama point are negtive. Near gama point, i just selected one q, whose > TA is negtive, to calculate the phonon, but the value of the TA is > positive. I thought the q mesh is small, so i chose 6*6*6 mesh. > > > Does the 6x6x6 mesh include also the points you calculated for checking. > > The 6*6*6 mesh dosen't include the above modes which has negtive > values, but i cannot find other ways to avoid the unexpected negtive > A values. > > thank you for your advice. > best regards > Li Yan > > > > > > > > --------------------------------- > ????????????????????????????????????????????????????
