<div dir="ltr"><div>I have calculated the phonon dispersion of orthorhombic RbPbI3 (Pnma) using
"PHONON" as implemented in Quantum Espresso and found the negative
frequencies ( which should not be present as suggested in <a href="https://doi.org/10.1063/1.5131575">https://doi.org/10.1063/1.5131575</a>). It would be great help if you suggest to me where I am doing
wrong!!! I have provided the computational details below:</div><div>1) The structure first is being relaxed and then the convergence tests are performed for Ecut, Kmesh and Lattice parameters.</div><div>2)
Using the relaxed structure with converged parameters, SCF is performed
with cov_thr=1.0d-8 (ecutwfc=70, ecutrho=600, kmesh=12*6*3); phonon
calculation is performed with tr2_ph=1.0d-14 at Gamma point, frequencies
are obtained by imposing acoustic sum rule at the Gamma point with
asr=simple.</div><div><br></div><div>Thank you!!<br></div><br clear="all"><br>-- <br><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div>With regards</div><div>Anupriya Nyayban</div><div>Ph.D. Scholar</div><div>Department of Physics</div><div>NIT Silchar<br></div></div></div></div>