Are FFT grids (NGX,NGY,NGZ) effective in a simulation with ML_MODE=run?

[xiancai]

Dear VASP developers,

I am performing a simulation using a generated machine-learning force field (ML_FF) with ML_MODE=run. At the beginning of the output file, a warning appears stating: “Your FFT grids (NGX,NGY,NGZ) are not sufficient for an accurate calculation. Thus, the results might be wrong. Good settings for NGX, NGY and NGZ are 6, 6 and 6, respectively.” The full message is shown in the enclosed figure.

According to my understanding, the FFT grids (NGX,NGY,NGZ) are only relevant for first-principles calculations, and thus, this warning can be disregarded. I would like to confirm whether my understanding is correct. Thank you for your time!

Sincerely,
Tian Hua

[martin.schlipf]

Yes, your understanding is correct. In ML_MODE = run, VASP does not need to perform FFTs so it is not important that NGX, NGY, and NGZ are large enough.