the IFC should be symmetric w.r.t. exchange of the two atoms and
displacement directions as a consequence of being second order
derivatives. other symmetries may apply in specific cases.
difficult to comment more without more info on what you are looking for.
stefano
On 11/10/2014 09:16 AM, Navaneetha Krishnan wrote:
Hello QE users,
I was investigating the IFCs generated by q2r.x after scf and ph
calculations. It looks like the force constant matrix for certain
pairs of atoms is not symmetric (with respect to the cartesian
coordinates). For silicon, the IFC matrices have to be symmetric with
respect to the cartesian coordinates - right? For aluminum, the output
is symmetric, as expected. Any thoughts?
Thanks a lot!
--Navaneeth
Caltech.
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