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
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