Thank you Professor Postnikov, Here I will provide two examples of my work I have a hexagonal structure containing 18 atoms 1. I have substituted one atom with a gaseous one and relaxed it up to 0.000794 eV/A and 0.00458798 kBar then I calculated the phonon and fortunately, there is no negative frequency while the force for the first step is approximated as 0.008174 eV/A
2. I have substituted two atoms with two gaseous ones and relaxed it up to 0.000549 eV/A and 0.00290065 kBar then I calculated the phonon and unfortunately, there are frequencies as -206.30292747012965 while the force for the first step is approximated as 0.015862 eV/A For both cases, I have used same inputs as For relaxation: MeshCutoff 870 Ry DM.MixingWeight 0.02 DM.NumberPulay 3 %block kgrid_Monkhorst_Pack 6 0 0 0.0 0 6 0 0.0 0 0 1 0.0 %endblock kgrid_Monkhorst_Pack For phonon: MeshCutoff 750 Ry DM.MixingWeight 0.02 DM.NumberPulay 8 %block kgrid_Monkhorst_Pack 3 0 0 0.0 0 3 0 0.0 0 0 1 0.0 %endblock kgrid_Monkhorst_Pack I repeated phonon calculation for the second case with %block kgrid_Monkhorst_Pack 6 0 0 0.0 0 6 0 0.0 0 0 1 0.0 %endblock kgrid_Monkhorst_Pack and the resulting force for the first step is 0.013928 eV/A I'm confused about what is happening in these two similar examples. [image: image.gif] [image: Mailtrack] <https://mailtrack.io?utm_source=gmail&utm_medium=signature&utm_campaign=signaturevirality5&;> Sender notified by Mailtrack <https://mailtrack.io?utm_source=gmail&utm_medium=signature&utm_campaign=signaturevirality5&;> 09/07/21, 01:54:22 AM
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