[QE-users] Problems with Relax and EPC Calculations in QE

[谢征奥]

Dear QE Community,
I hope you are having a productive day and that your research commitments are not overly demanding. Allow me to introduce myself: I am Xie, a Chinese researcher, and I am new to using QE (Quantum ESPRESSO). I have a strong interest in computational physics, which has led me to deepen my application of this software for my research projects. I am writing today to ask three specific questions regarding the calculations I am conducting, as I have encountered some difficulties and greatly value your expertise and extraordinary experience in the field of QE, given that you are one of the core developers of the software.
When performing phonon spectrum calculations with QE, what is the correct sequence of steps for structural relaxation? Should I first run a vc-relax calculation, then increase the force and energy convergence thresholds before performing a subsequent relax calculation? Or is it sufficient to verify the convergence of the total stress from the vc-relax results and use them directly for subsequent calculations? In my case, the pressure obtained from vc-relax has met my convergence criteria, but when I used the optimized structure to run a relax calculation, the pressure value became significantly higher: is this a reasonable behavior?
When using the pw.x module, which parameters have a significant impact on eliminating imaginary frequencies?
During the structural optimization process, is it acceptable to always use the parameter ibrav=0 in the relax.in input file?
Thank you in advance for the time you will dedicate to my questions and for your valuable guidance. As a novice in QE, every suggestion will be fundamental to advancing my learning journey and ensuring the success of my calculations. If you require any further details about my input files or the results obtained, I would be happy to provide all the necessary information.
Sincerely,
Xie
Chinese Researcher

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