My Community

Hi all,
In my calculation i didnt set the NPAR tag and got this warning;

For optimal performance we recommend that you set |
| NPAR = approx SQRT( number of cores) |
| This will greatly improve the performance of VASP for DFT. |
| The default NPAR=number of cores might be grossly inefficient |
| on modern multi-core architectures or massively parallel machines. |
| Unfortunately you need to use the default for hybrid, GW and RPA |
| calculations.


Does it affects the result of the calculation or just increase the required time for calculation?

thank you

I'm not sure but the result should not be altered by the NPAR setting. Isn't it?

I usually use NPAR=sqrt(# of cpus) for DFT. For hybrid calculations, I use the default, i.e., NPAR=# of cpus. I have noticed that NPAR does affect the number of bands. So if you set NBANDS=26 in the INCAR and you use NPAR=30 (for say HSE with 30 cpus), then in the OUTCAR, you will find NBANDS=30 and not 24. Somehow, VASP increases NBANDS to make it divisible by NPAR.

Vahid