How to calculate ZPE using Quantum Espresso

Posted In DFT (Quantum Espresso)
  • Jayfe Anthony Abrea 3 months ago

    Hello Materials Square!

     

    I've read your QE blogs and they are very informational. Thank you for it.

     

    I hope that you can provide a tutorial for us in calculation of ZPE for the adsorbate that is adsorbed in the slab. For example, an oxygen atom adsorbed in the four-fold hollow site on a 2x2 slab of Fe(100). I'm not sure how to do it but I've read that I would be doing a phonon calculations. Is it correct? I tried doing it but it didn't converged for almost a week.

     

    I hope you could help us who are doing this research. Thank you!

     

     

  • Materials Square 3 months ago

    Yes, it is. The phonon will take very high computational resources, generally.

    For that, multi-step relaxation will be helpful.

    It means that, optimizes your structure with general setting -> and next, start rigorous optimization with phonon settings.

    And also, optimize each component separately will be helpful: Slab, adsorbate, system.

     

    These steps will be proper for you.

    1. Optimize the metal unit cell

    2. Make slab structure with the optimized unit cell

    3. Optimize the slab structure with general settings

    4. Load the optimized structure

    5. Start a new optimization calculation for the slab of 4, with rigorous settings

    6. Adsorb an optimized molecule to the precisely optimized slab model

    7. Start optimization for structure 6 with rigorous settings

  • Jayfe Anthony Abrea 3 months ago

    Hello Materials Square,

     

    I appreciate your reply and thank you very much for helping me out with this calculation. I was able to do the optimization down to the system itself. I was able to adsorbed the optimized atom to the optimized slab model.

     

    I just want to ask about the rigorous settings for step 7 that you mentioned. Should I be "freezing" the slab and make the adsorbate mobile when setting the phonon calculation? Since I my computation to be as less costly as possible, I just want to trim down my focus into the frequency (or frequencies) on the vibrational mode of the adsorbate, in this case for example, the oxygen atom only. Is it possible to do computations only on the vibrational mode of the adsorbate only? How do I do it?

    Best regards,

    Jayfe

  • Materials Square 3 months ago

    Hello Jayfe Anthony Abrea

     

    The Phonon module does not support atomic fix.

    Because, to describe the vibration, you have to give a physical displacement or give a perturbation to the wavefunction. However, since this becomes impossible when the structure is fixed, the phonon calculation is not performed properly.

    But this is for the general.

    Of course, as you said, you can compute it by fixing only the substrate (slab).

    However, it is not currently provided by MatSQ because there are several limitations such as having to calculate only the gamma point.

     

     

    Thank you.

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