Thank you for your reply. It helped me a lot to understand it. On Thu, Jul 10, 2025 at 12:38 PM Lorenzo Paulatto <lorenzo.paula...@cnrs.fr> wrote:
> Hello, > > you cannot do second order Raman with ph.x alone, because second order > Raman come from two-phonon excitation, and ph.x does single phonon. If you > do the phonon calculation at Gamma with lraman=.true. and then process the > file with dynmat (or by hand, it is a really simple formula) you can get > the Raman cross-section for each individual phonons. > > You can however compute two-phonon vinrational spectra using the d3q.x > code and tools. The "spectral weight" functionality of the linewidth code > (d3_lw.x), as shown the in the MgO example that should be available in the > last version. There are three caveats: > > 1. The Raman cross-section is not taken into account, but it can easily be > included afterwards : the code produce one specrum per phonon band, it is a > reasonable approximation to just use the cross-section of the unperturbed > phonon (as produced by dynmat.x) and multiply by hand. > > 2. This code can do two-phonon spectra, which you then couple to light via > the Raman cross-section. I.e. the photon excite a phonon which the decays > to two phonons. There is an additional term, which correspond to direct > excitation of two phonons from one photon via a higher order dielectric > response. The equation is written in R. A. Cowley, Reports on Progress in > Physics 31, 123 (1968), and the matrix element can be computed by doing > finite difference derivation of the Raman cross-section, I know it has been > done in very simple materials, but afaik nobody as ever published a code to > do it easily. > > 3. Metallic systems and resonant Raman is a completely different story. > > kind regards > On 10/07/2025 01:03, Gulshan Kumar via users wrote: > > Hi everyone, > How can we do post-processing for second-order Raman modes? If anyone has > done it, please provide me with details. > I have done ph.x, q2r.x, and matdyn calculations. > > Thank you > gulshan > > _______________________________________________________________________________ > The Quantum ESPRESSO Foundation stands in solidarity with all civilians > worldwide who are victims of terrorism, military aggression, and > indiscriminate warfare. > -------------------------------------------------------------------------------- > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list > users@lists.quantum-espresso.orghttps://lists.quantum-espresso.org/mailman/listinfo/users > > -- > Dr. Lorenzo Paulatto > IR IMPMC - CNRS UMR 7590 / Sorbonne Université / MNHN > phone: +33 (0)1 442 79822 / telegram: lpaulatto > http://www.impmc.upmc.fr/~paulatto/ - https://anharmonic.github.io/ > 23-24/423 B115, 4 place Jussieu 75252 Paris CX 05 > > _______________________________________________________________________________ > The Quantum ESPRESSO Foundation stands in solidarity with all civilians > worldwide who are victims of terrorism, military aggression, and > indiscriminate warfare. > > -------------------------------------------------------------------------------- > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list users@lists.quantum-espresso.org > https://lists.quantum-espresso.org/mailman/listinfo/users
_______________________________________________________________________________ The Quantum ESPRESSO Foundation stands in solidarity with all civilians worldwide who are victims of terrorism, military aggression, and indiscriminate warfare. -------------------------------------------------------------------------------- Quantum ESPRESSO is supported by MaX (www.max-centre.eu) users mailing list users@lists.quantum-espresso.org https://lists.quantum-espresso.org/mailman/listinfo/users
