[QE-users] IR calculation for oriented single crystal

[Lorenzo Paulatto]

Hello Zack,
the code that computes the IR cross sections is in subroutine RamanIR at line 150 of file LR_Modules/dynmatsub.f90. If you ignore the Raman parts, it is literally 10 lines:

do nu = 1,3*nat
do ipol=1,3
polar(ipol)=0.0d0
end do
do na=1,nat
do ipol=1,3
do jpol=1,3
polar(ipol) = polar(ipol) + &
zstar(ipol,jpol,na)*z((na-1)*3+jpol,nu)
end do
end do
end do

infrared(nu) = 2.d0*(polar(1)**2+polar(2)**2+polar(3)**2)*irfac
... some raman stuff ...
endo do

It should be straightforward to adapt it to whatever you need. Keeping in mind that "zstar" is the effective charge matrix of atom "na" and z(3nat, 3nat) is the matrix of phonon polarizations.
Otherwise, you can have z printed by dynmat by setting the variable
fileig = 'file_name.txt'
and then do the calculation in some other way.

hth
Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
phone: +33 (0)1 442 79822 / skype: paulatz
http://www.impmc.upmc.fr/~paulatto/ - https://anharmonic.github.io/
23-24/423 B115, 4 place Jussieu 75252 Paris CX 05
On Mar 18 2022, at 6:23 am, Zack Gainsforth <zackg at berkeley.edu> wrote:
> Hi All,
>
> I have set up a calculation using pw.x -> ph.x -> dynmat.x successfully and plotted myself an IR spectrum. The match to the experimental spectrum is good. However, this is an IR spectrum assuming a powder where the photons are exciting all the modes. I’d now like to calculate the spectrum for a single crystal and specify the electric vector of the photon relative to the crystal. It should preferentially excite certain modes.
> Is there a straightforward way to do this using ph.x + dynmat.x? Or perhaps a way to read/print the dipole vectors for each mode so I can dot it with my photon’s e-field? Or another way of thinking about this which is more efficient? (Maybe I missed something in the documentation!)
> Thanks,
> Zack
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