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[jinhong zhang <zhangjinhong2009@gmail.com>]

Dear Abiniters

 

I recently calculated phonon dispersion of B12P2 following the RF tutorial. I first optimized the geometry of the material by GGA and the tensor stress in the material reached e-7, which i believe is accurate enough. And the ngkpt I chose first time is 4 4 4 and ecut is 15. The result of phonon dispersion turned out to be bad, some low frequencies appeared negative and even reached -700cm-1 (but the acoustic frequencies are 0 at Gamma point). And then I changed the ngkpt to 8 8 8 and ecut to 17, and optimized and calculated again, the graph turned out to be better but still not good, only 3 acoustic frequencies represented negative beyond Gamma point this time, and the magnitude reached about -500cm-1max.

 

I was wondering the reason. Is the problem of ABINT or somewhere i set incorrect? (I preferred the later:P) or the stability of this material is not good? But my teacher had calculated the phonon dispersion of B12O2-a similar one-by Material Studio, which the result was good.

 

Hope any Abiniter can give me some advices and help me solve the problem, i would be very appreciated.

 

Best regards

 

Fan