[Pw_forum] Negative Phonon Dispersion after geometry optimization twice.

Mohammed Ghadiyali m786g at live.co.uk
Wed Sep 7 10:47:56 CEST 2016

Dear All,
After performing the geometry optimization twice, I am still getting negative phonon dispersion.

For first geometry optimization I used following tags
calculation = 'vc-relax' ion_dynamics = 'bfgs'
cell_dofree = 'shape' 

And for second time I used following tags
calculation = vc-relax'
ion_dynamics = 'bfgs'
cell_dofree = '2Dxy' 

The system I am working on is a 2D buckled tin, can someone help me out and inform me as how should one proceed with
geometry optimization.  For Phonon Dispersion calculation I have used phonon package induced in QE as well as phononpy.
I have also included my input file, please check the attachment for the same.
Ghadiyali Mohammed Kader. 		 	   		  
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