[QE-users] symmetry traces in sym_band.f90

[Gerson J. Ferreira]

Dear QE users,

I need the matrix representation for the symmetry operators in the basis of
the QE bands, so I'm checking how to edit the file sym_band.f90 for this
purpose.

The SUBROUTINE find_band_sym_so already calculates the trace as (loops are
implied)

> trace(iclass,igroup)=trace(iclass,igroup) + DOT_PRODUCT
> (evc(:,ibnd),evcr(:,ibnd))


So, at first I imagined that a simple change would allow me to get the full
matrices as (loops are implied)

> matrep(iclass,igroup,i,j) = DOT_PRODUCT (evc(:,ibnd),evcr(:,jbnd))


But I've noticed that the traces are "wrong". If I print as

> PRINT *, 'Class:', name_class_so(iclass)
> PRINT *, 'Trace:', trace(iclass,igroup)

Both the trace and the matrices (matrep) above don't match the expected
results. For instance, all double group bar-irreps are showing trace = 0.

In the second part of this subroutine, where the code identifies the
symmetry representations, I don't understand some of the IFs there, and the
meaning of the variable "shift". So I guess I'm misreading something.

Could someone help me understand what I am doing wrong?

Best,
--
Gerson J. Ferreira
Prof. Dr. @ InFis - UFU
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gjferreira.wordpress.com
Institute of Physics
Federal University of Uberlândia, Brazil
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