[QE-users] Confusion regarding the optimization of a tetragonal structure with pressure

[Anupriya Nyayban]

Dear users and experts,

I am conducting a study on the pressure effect on a tetragonal structure. I
have followed the following steps to determine the lattice parameters at
different pressures:

1)Relaxation of the initially reported experimental structure.
2)Testing the convergence of parameters such as energy cutoff (ecut),
k-point mesh (kmesh), and lattice parameters by varying celldm(3).
3)Applying the Murnaghan equation to obtain volumes and lattice parameters
associated with different pressures based on the data from the
lattice-parameter convergence.
4)Performing relaxation and lattice-parameter convergence (by varying
celldm(3)) for each structure corresponding to different pressures.

After the calculations, I obtained the following volumes and pressures:
0 GPa       2799.87 (au^3)
5 GPa       2799.11 (au^3)
10 GPa     2807.17(au^3)
15 GPa     2814.35(au^3)
20GPa      2760.07(au^3)
25GPa      2680.36(au^3)
30GPa      2755.89(au^3)

I am concerned about the observed increase in volume with increasing
pressure. I would appreciate your help in identifying any mistakes I may
have made in the steps outlined above.

Thank you for your assistance.

With Regards
Dr. Anupriya Nyayban
Postdoctoral project associate
IIT Madras
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