Sorry forgot half of the answer
acustic branches should be flat along k_z direction, I would check that
is so. If it is not so, maybe you are adding non physical interactions
between periodic images and this can cause the numerical instabilities.
I don't know whether your program is able to clean spurious
interactions due to fake periodicity.
I hope this helps - pietro
On 05/12/2016 09:52, Pietro Delugas wrote:
Then one of the 3 acustic branches ( probably the one you gave
problems with ) should be flat.
I don't know how this phononpy works, maybe there is a way to deal
directly with 2D systems, otherwise just find a way to set to 0 all
the interatomic force constants that correspond to interactions
between atoms staying in different periodic images of the slab.
pietro
On 05/12/2016 09:33, Mohammed Ghadiyali wrote:
Hi,
The structure is two dimensional similar to bi-layer graphene.
Regards,
Ghadiyali Mohammed Kader
Research Scholar
University of Mumbai.
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