Orbital orientation - axis alignment

kaneod · Post by **kaneod** » Mon May 07, 2012 9:56 am

Hi all,

I've been checking and making some changes to the optics_paw_core and conducti_paw_core routines and have been checking the outputs against a simple carbon-carbon dimer in a big box. The conducti utility now works as expected, but I've noticed that the KS orbitals are not aligned along the x and z directions in the cell. See attached images as an example. In this case, the unoccupied band 6 of the C2 dimer is slightly tilted with respect to the x and z axes. I'm curious to know why this is!

I suspect it would not be a problem in a molecule with less symmetry. I'm interested in NEXAFS spectra and the orbital orientation relative to the electric field direction is important in the actual experiments.

Note that I know physically that symmetry considerations mean that there is no real preferred orbital direction - what I want to know is why the orbitals come out at the slightly tilted angle in Abinit in particular.

Kane