[Pw_forum] About getting Raman Spectrum for a 24 atom-hybrid halide perovskite

[Ari P Seitsonen]

Dear Josue Clavijo,

   Do you mind sending the input for both 'pw.x' and 'ph.x'? Then we would 
better understand - for example which pseudo potentials you use etc - what 
you are doing and if we find some aspect that should be improved to get 
the calculations running normally; it is not common, at least in my 
limited experience, that one should increase the 'tr2_ph' that much, as 
this is also a material with quite a band gap, isn't it?

     Greetings from Sunny Montrouge,

        apsi

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   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
     Ecole Normale Supérieure (ENS), Département de Chimie, Paris
     Mobile (F) : +33 789 37 24 25    (CH) : +41 79 71 90 935


On Tue, 9 Feb 2016, Josue Itsman Clavijo Penagos wrote:

> Dear all, I apologize for sending a former e-mail from another account other
> than the subscribed one.
> 
> So, here is my post again:
> 
> I’m having trouble to replicate the result for the raman spectra for some
> hybrid perovskite, namely CH3NH3PbI3, a.k.a MAPbI3 (4 MAPbI3 molecules/unit
> cell). I'm using the relaxed cell and atomic coordinates as in J. Phys.
> Chem. Lett., 2014, 5 (2), pp 279–284.
> 
> So, I’d really thank you any advice and words of correction regarding to the
> following issues:
> 
> 1-The thing is that my phonon calculations never converge, even using an
> energy cutoff in the scf previous calculations of 1D-12. (Using
> Norm-conserving LDA-level PZ PPs). WIll be necessary to lower the tr2_ph
> value in ph.x to something greater than 1D-12 since the system is somewhat
> huge (24 atoms)?
> 
> 2- In a latter ph.x run attemp, I set the tr2_ph value to 1D-8 and the the
> initial convergence was achieved, but at the stage of calculation the second
> derivatives, roots never converged, so i can not get the dynamical matrix
> anytime.
> 
> So, for as a huge system as MAPbI3 is, It is likely to exist special
> constraints, adjustments or requirements i'm missing, in order to get the
> dynamical matrix and, using dynmat.x and other plotting tools, to simulate
> the raman spectrum with the quantum espresso suite?
> 
> Excuse me if i’m missing several important theoretical or QE-related
> aspects, but i really need some advice about all of this stuff.
> 
> Best regards,
> 
> -------------------------------------------------------
> Dr.Sc. JOSUÉ CLAVIJO, Chem.
> Christian, born again
> 
> Assistant Professor
> Universidad Nacional de Colombia
> Science College
> Chemistry Department
> 
> 
> 
> 
>