[QE-users] Negative phonon frequency

[Artur Durajski]

Dear Users and Developers, 
I'm trying to calculate the phonon and electron-phonon properties of a simple conventional superconductor. I followed the standard procedure using pw.x -> ph.x -> q2r -> matdyn.x -> lambda.x. 
This led to an unexpected situation. In the elph_dir directory, the values in the elph.inp_lambda.X files are positive, and in the lambda.out file, I successfully calculated the lambda, omega_log and T_c values, which all seem correct. However, I encountered negative values in the phonon.dos file. 
My question is: why does the alpha2F generated from lambda.x has positive values while the phonon.dos has some negative values? 

Best Regards 
Artur 
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Czestochowa University of Technology 
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