[QE-developers] [Problem] the relaxation of the charged systems: use of the tot_charge option

[‍홍은서[학생](이과대학 물리학과)]

Dear QE developers,


Hello, I’m  Eunseo Hong who is an undergraduate student in Kyunghee university, Korea, having an internship in DFT lab.

I have a question on the use of tot_charge option in PWscf.
I’ve followed up with the paper (DOI:https://doi.org/10.1103/PhysRevB.94.024501) to reproduce it, and now I’m taking time in researching the relationship between the superconductivity of doped MoS2s, and the stacking orders, which means the bulk materials, such as ABC staking, ABA stacking, and so on. However, when I relax my materials over the specific tot_charge values using 'vc-relax’ calculations, the convergence of the relaxation totally failed. (I almost put in effort over the several hundred hours, I even tried to use cp.x to use steepest descent algorithms since I tought the geometric relaxation algorithms in pwSCF are based on the thought that equilibrium structure has the minimum energy and vice versa, which means the lowest energy, so I tried purely force-based optimization algorithm to obtain the 0 pressures and 0 forces structure, and efforts so on…) So I tried to plot the energy contour of the structure with various a and c lattice constants, and the result was surprised. There are no minimum points, but rather the so-called energy descent, I don’t know how to explain it. I wonder the reason of this situation if it is a physical fact, or a result of the quantum espresso program, as I searched, since quantum espresso use the periodic boundary condition, there usually might be divergences of scf calculations when ones relax the charged system due to column interactions, or other reasons.

I appended one of my calculations which are problematic.


I would be very grateful if you could reply to my email.

Best regards,


  *
Eunseo Hong
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