[Pw_forum] Eigenvectors

[Michael Malorny]

Dear pwscf users,

I am currently trying to calculate the scattering cross sections of
wurtzite CdS and CdSe semiconductors. As I am planning to investigate
mixed crystals formed by these two systems in the future I also take
supercells of the pure materials into account.

For the calculation of the scattering cross section the eigenvectors of
the dynamical matrix are needed which I extract amongst other things from
the program matdyn of the pwscf-2.0-package.

I calculated the cross section of CdS with wurtzite structure and of CdS
supercells generated by expanding the wurtzite cell by the factors 2x2x2
and 4x4x4, respectively. As expected, the cross sections of the three
systems are identical at the Gamma and the A point of the first BZ. But at
all other points in between the cross sections differ more or less.

Has anybody an explanation for this strange behaviour or can even help me
solving my problem? I found out that the eigenvectors possess imaginary
parts even at the Gamma point which shouldn't occur in my understanding.
Could this be an explanation and if so, is there a possibility to
circumvent this problem?

Best regards


Michael Malorny