[Pw_forum] Symmetry of IFCs (Harmonic) for Si

[stefano de gironcoli]

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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