My Community

The purpose of performing HSE calculation is to obtain more accurate structure parameters and corresponding properties.
However, I found that many researchers perform HSE calculation as the following: first, do PBE geometry optimization and then using HSE only for energy evaluation. That is, both PBE and HSE calculation using the same structure parameters. Is such HSE calculation right?

Meanwhile, some researcher performs geometry optimization by HSE. I know generally, accurate geometry optimization is performed by the calculation of series of energy E and volume V, then fit the equation of states and finally obtained the equilibrium volume Vo corresponding the lowest energy.
My question is ?Can HSE be employed to perform geometry optimization simply by assigning NSW=40, ISIF=3??

xiaogai,

Yes, you can do geometry optimization with HSE. And yes, you should set ISIF=3 for any HSE calculation. You can set NSW to however many geometry optimization steps you want to take; 40 is often a good number.
The reason many researchers do geometry optimization in PBE and then calculate energy from HSE is because the HSE functional is MUCH MUCH slower to use. For example, in a recent calculation I did on MoO2, I found that converging the energy using HSE took 3250 times longer than converging the energy with PBE at the same k point grid, energy cutoff, etc. The reason many researchers do only energy calculations and not full geometry optimizations at the HSE level is because it would take too long, or be too expensive. A single geometry optimization at the HSE level might use up your entire allocation of computer time, where the same amount of time could be used to run hundreds of calculations with PBE. With small, insulating systems that have few electrons and need few k points, geometry optimization at HSE might be possible. For big systems, unless you have a lot of computer time and a lot of patience, geometry optimization with HSE is probably not an option.

I hope that answers your question!