VASP Forum

Dear experts,
I am performing optical-properties calculations within the RPA framework and would like to confirm whether my workflow is correct. My procedure is as follows: Step: 1 Ground-state DFT: I performed a standard DFT calculation and generated the WAVECAR.
Step 2: Generation of WAVEDER: In the second step, I used
ISTART = 1
NBANDS = two times of NBANDS what I obtained in step1
ALGO = Exact
LOPTICS = .TRUE.
CSHIFT = 0.1
This step successfully produced both WAVECAR and WAVEDER.
Step 3: RPA dielectric function
In the third step, I used
ISTART = 1
NBANDS = same as in step 2
ALGO = CHI
LRPA = .TRUE.
My main questions are:

1. Is this workflow correct for obtaining the dielectric function using RPA in VASP?
2. Parallelization issue:
In steps 1 and 2, parallelization works normally with NCORE = 24

However, in step 3, using ALGO = CHI, VASP stops with an error when NCORE is included in the INCAR. I also added NPAR= number of nodes in my INCAR, but still the same error is coming.
Should parallelization work for the CHI step?
Do I need to remove NCORE for this step?

3.Choice of NOMEGA:
What would be an appropriate value of NOMEGA for the third step? As my walltime is 24 Hrs.

I am attaching the error screenshot, obtained in 3rd step.

Dear Alok Shukla,

For general workflows you can take a look on our tutorial pages about optical properties. I would recommend to take a look at the following pages in the VASP wiki:
https://www.vasp.at/tutorials/latest/bse/part1/
https://www.vasp.at/tutorials/latest/bse/part2/
https://vasp.at/wiki/Optical_properties ... -_Tutorial
You will find general workflows there not only using the RPA but also BSE and GW. I think this might be helpful to you.

The error which you are experiencing is telling you that VASP is trying to change the internal KPOINTS settings. This is necessary in the calculation step you are doing. The code is running in parallel but is only able to do so if the NPAR is set to the number of nodes. As recommend in the error message just remove the NPAR tag from your INCAR file.

All the Best Jonathan