While trying to do 'vc-relax' using pw.x in Quantum Espresso for MoS2 unit cell, I have developed a confusion regarding the selection of the cell parameters to be moved in cell_dofree card. As under the &SYSTEM, I have given 'ibrav= 4' for MoS2 unit cell (hexagonal lattice) and vacuum in the z-direction. Will it affect the vacuum if I proceed using cell_dofree= 'ibrav'? So in this kind of situation what is the more accurate choice in cell_dofree card during relaxation?
Any suggestions will be highly appreciated.
Thanks in advance.
Since you have a vacuum, you must refrain from using cell_dofree= 'ibrav' or any other option that changes the lattice shape along the vacuum axis. With such options, pw.x gets confused, as it can not find a global potential valley no matter how it varies the lattice parameters. As a result, you'll end up with a wrong structure. For your purpose, you can either use the option 2Dxy, or alternatively, do only ionic relaxation for a set of manually-selected lattice parameters. I suggest the latter, because it seems you want to keep the hexagonal symmetry of the system, and so any change in v1 and v2 will be the same.
Thank you Mohammad Saeed Bahramy. You are right. I wanted to maintain the hexagonal symmetry of the system during relaxation. I will definitely try both the options (2Dxy and ionic relaxation) suggested by you. Hopefully, it will solve my problem.
Hi, What will be the command to do the ionic relaxation Sameer Kumar Mallik ?
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