# How does electronic iteration work in a VASP relaxation calculation?

I am a beginner using VASP to do material modeling, and I'm confused about the following questions:

1. How does the electronic iteration work in VASP relaxation calculation?
2. Is the electronic iteration during structure optimization and the same as that done in a single static self-consistent calculation?

If they are the same, it seems that there is no need to perform a static self-consistent calculation after structure optimization. In the last ion step of structure optimization, the calculation converges and atom position will not change further, electronic iteration at this point should be equivalent to electronic iteration in the subsequent self-consistent calculation.

The figure below represents very well the self-consistent field (SCF) procedure used to solve the Kohn-Sham (KS) equations under the Density Functional Theory (DFT) approach:

In the convergence test, if the electronic density isn't converged, the calculations return to second step, using that density as input to calculate the effective potential.
If the electronic density is already converged, then all the desired properties are calculated using the converged electron density.

Yet, we have two type of calculations: single-point and relaxation.
In single-point calculations, there is no structure relaxation so the system geometry is static, but the electron relaxation is done. In relaxation calculations, the system structure is also relaxed/optimized (can be only the atoms positions or the atoms positions and the cell parameters).

• thanks，In relaxation calculations, both system structure and electron are relaxed，In single-point calculations，only electron relaxation is done. you mean electron relaxation in two kinds of calculations is the same？so why single-point calculation has always been performed after structure optimization？ Dec 2, 2021 at 12:31
• Yes, the electron relaxation or self-consistent field (SCF) procedure is the same for both calculations. The only need to run a single-point after a relaxation is when you want to calculate properties that can not be calculated at the same time. Personally, I always prefer to run just a relaxation calculation (that consumes times), and after that use the relaxed output in a new single-point calculations where I obtain the properties.
– Camps
Dec 2, 2021 at 13:23
• Thank you very much！ Dec 3, 2021 at 1:32