4) Other steps for optimization, for Quantum Espresso input file

On this page, there will be lots of other preparation processes before the final input file modelling. I didn’t have time to write a thorough explanation.

  1. after finding the cif file and changing it to the input file:
    1. “relax” calculations to find the proper atomic position for the current lattice parameters
    2. “VC-relax” calculation for finding the best lattice parameters and volume of the lattice and also the position of atoms. more complete than the “A” calculation but needs a long time.
    3. The shape of the unit cell optimization for the given volume. it is also found by minimizing the energy for the given volume, by optimizing a,b,c, alpha, beta and gamma. e.g for an hcp crystal, at diff volume we optimize c/a at different values. This is a hard process, so we will use a stress tensor in QE.

Note: ev.x command in the terminal could fo the volume optimization and gives the bulk module. It just needs a text file of different volumes and corresponding energy that you have created before.