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How many GB of RAM would be needed for VASP to evaluate optical properties of a material?

Matter Modeling Asked by Anibal Bezerra on December 5, 2020

Even though it is a powerful tool, Quantum ESPRESSO’s hardware requirements are very high. For instance, to evaluate optical properties, even for structures with tens of atoms, Quantum ESPRESSO can require more than 100GB of RAM. What about VASP?

One Answer

This question is kind of general. I will outline some points related.

  • Firstly, it depends on the theoretical levels that you use to calculate the optical properties. In general, there are three levels:

    • Independent level;
    • RPA (random phase approximation) level;
    • GW&BSE level;

The first one is memory friendly in terms of the empty bands contained. However, the last two are very memory-consuming even for a small system.

  • Secondly, it depends on how large your system and whether includes the spin-orbit coupling or not.

  • Thirdly, you must test the parameters to obtain converged results. All these parameters are closely related to memory consumption. In VASP, the key parameters are:

    • KMESH
    • ENCUT
    • BANDS & ENCUTGW
    • NBANDSV
    • NBANDSO

For your example with tens of atoms, to obtain converged results I believe 100G memory is not enough in VASP. In summary, you can test it and get some feeling.

Answered by Jack on December 5, 2020

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