[QE-users] reflection-absorption IR spectra

[Michal Krompiec]

Dear Paolo,
Thank you, this is what Lorenzo Paulatto suggested, too:
the dynmat.x (not matdyn.x) code computes the IR cross section, if you
give it in input the dynamical matrix at Gamma with effective charges.
In recent versions of the code, the calculation is done in
LR_Modules/dynmat_sub.f90, subroutine RamanIR, and it is quite
straightforward. At a certain point the IR cross section is computed as

     infrared(nu) = 2.d0*(polar(1)**2+polar(2)**2+polar(3)**2)*irfac

So, replacing this by:
infrared(nu) = 2.d0*(polar(3)**2)*irfac
should do what I want (only the Z component of induced dipole is IR
active). I'll do some tests soon...

Best regards,
Michal


On Fri, 8 Jan 2021 at 11:43, Paolo Giannozzi <p.giannozzi at gmail.com> wrote:

> The dipole induced by a phonon can be computed from phonon displacements
> and effective charges: see variable "polar", computed in routine RamanIR,
> file LR_Modules/dynmat_sub.f90, called by PHonon/PH/dynmat.f90
>
> Paolo
>
> On Thu, Jan 7, 2021 at 10:58 PM Michal Krompiec <michal.krompiec at gmail.com>
> wrote:
>
>> Hello,
>>
>> In Reflection-Absorption IR (IR at grazing incidence), only modes that
>> induce a nonzero dipole in the direction normal to the surface contribute
>> to the spectrum. Is it possible to simulate this in QE?
>> In other words: how do I calculate the IR spectrum of flexural phonons of
>> a 2D system?
>>
>> Best regards,
>>
>> Michal Krompiec, Merck KGaA
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>
>
> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
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