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

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.