[Wien] local rotation matrix - followup question on triclinic systems

[Cormac McGuinness]

Dear all

I have a followup question regarding the local rotation matrix and global and
local coordinates as applied to triclinic unit cells, for instance many organic
molecular solids (e.g pentacene), though the same question could apply to
complex metal oxides. (note the question is not specifally about pentacene)

In the case of a triclinic crystal where every inequivalent site has a
pointgroup symmetry of 1, the calculation then gives the identity matrix as the
local rotation matrix for each and every inequivalent site. Should one interpret
the direction of the x, y, and z projected axes of the orbitals as being the
same for all of the sites ?

If so then is the x direction parallel to the crystal axis a ?
What then determines how y and z are oriented as the crystal axes a,b,c are not
orthonormal ? How should these directions be interpreted in this case.

I ask as for planar pi-conjugated organic molecules the most important axis to
distinguish is that perpendicular to the plane of the molecule. How can I know
for sure which direction in terms of the physical crystal structure is
associated with x, y and z in a triclinic system ?


If I want to replace this definition of x,y,z, can I simply rerun with my own
rotation matrix in place of each instance of the identity matrix, say to ensure
that one of x,y,z is perpendicular to the plane of the molecule, in the manner
described previously ?

Yours gratefully

Cormac


Quoting Igor Djerdj <Igor.Djerdj at mat.ethz.ch>:

> Dear all,
> I have a question concerning local rotation matrix. I have done and saved scf
> calculation using default values for local rotation matrix. Now, I want to
> change from global to local coordinate system to get dz2 and dx2y2 as bonding
> orbitals pointed with their lobes into oxygen. I changed in struct file local
> rotation matrix around V atom, and now the question is what should I do the
> next in order to calculate DOS, should I run the programs according the order
> in w2web interface or should I rerun again scf?
> Regards,
> Igor
>


--
Dr. Cormac McGuinness, Lecturer, School of Physics, Trinity College Dublin.
Phone: +353 1 8963547    Fax: +353 1 6711759    Office: SNIAM 3.17