Dear Nicola, I read the paper, but I still don't understand about the difference between primitive-cell calculations and density-functional perturbation theory at any arbitrary q wavevector. If I am only interesting in Gamma point (which q = 0, and other points in Brillouin zone not interested.), would it be ok to calculate Raman Spectra with only 1 unit cell, or do I need more unit cells to satisfy it? Best Regards, HY Lu
在 2023年11月13日 星期一 上午04:29:48 [GMT+8], Nicola Marzari<nicola.marz...@epfl.ch> 寫道: Dear all, I think there is a profound misunderstanding here - make sure you understand the difference between primitive-cell calculations and density-functional perturbation theory at any arbitrary q wavevector (read 2001 RMP by Baroni et al) and finite-difference calculations in a supercell, a-la phonopy. nicola Sent from a tiny keyboard... Contact info:http://theossrv1.epfl.ch/Main/Contact On 12 Nov 2023, at 17:29, ludwigboltzmann.s...@nycu.edu.tw wrote: Dear Mr. Kondrin, Thanks, this is exactly for silicon. Best Regards, HY Lu 在 2023年11月12日 星期日 下午02:52:03 [GMT+8], <mkond...@hppi.troitsk.ru> 寫道: Hi, Ludwig Raman modes should be calculate in primitive unit cell so you get the correct number of phonon modes. In silicon you get six modes -- triply degenerate Raman mode and three acoustic modes. Sincerely yours, M.V.Kondrin On Nov 12 2023, ludwigboltzmann.s...@nycu.edu.tw wrote: > Dear users: I am going to calculate Raman spectra for organic perovskite. > (only at Gamma point)My flow chart is like this: pw.x vc-relax(geometry > optimization)→pw.x scf→ph.x→dynmat.xIn Phonon Calculation for Raman > Spectra , How to decide to use how many unit cells? > > I saw what in the tutorial, for silicon in primitive cell, Si only has 2 > atoms in a primitive cell, and the tutorial used 2 atoms (1 unit cell to > calculate)Ref:https://www.quantum-espresso.org/wp-content/uploads/2022/03/phonons_tutorial_shanghai1.pdf > > > However, according to the paper I read, the author used 4 unit cells to > calculate, is this going to make some difference? Is it ok to > calculate Raman spectra with on one unit cell?Difference I could imagine > is that if I had 1unit cell with 24 atoms,With 1 unit cell (24 atoms), I > can get 72(3*24) modes at Gamma point. With 2 unit cell (48 atoms), I can > get 144(3*48) modes at Gamma point. With 4 unit cell (96 atoms), I can > get 288(3*96) modes at Gamma point. As the unit cell increased, I would > get more modes at Gamma point.However, it takes more time to do the > calculation.I'm wondering what's the difference to do phonon calculation > to use different number of unit cells? And how to decide it? Best > Regards,HY Lu _______________________________________________ The Quantum ESPRESSO community stands by the Ukrainian people and expresses its concerns about the devastating effects that the Russian military offensive has on their country and on the free and peaceful scientific, cultural, and economic cooperation amongst peoples _______________________________________________ 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 community stands by the Ukrainian people and expresses its concerns about the devastating effects that the Russian military offensive has on their country and on the free and peaceful scientific, cultural, and economic cooperation amongst peoples _______________________________________________ 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