Yambo Community Forum

Dear Developers,
I know the FFTGvecs is the number of G-vectors or energy cutoff for expanding wavefunctions in transition matrix elements and FFT operations, and adjusting that can regulate the memory of calculation. But I wonder how to determine it?
For example, I do the DFT calculation using 450eV for the first step. Is that meant to be that I should set the FFTGvecs to 450 eV?
The default value is 15529 RL when I generate the yambo input file.
Looking forward to your reply.

Dear Han Gao,

if you are not experiencing memory problem you can leave the default value.
If you need to lower it, a reasonable criteria is to look at the orthonormalisation of the wfs which is reported when calculating e.g. dipoles or HF self-energy:
e.g. and verify that it does not differ from 0,1 which means <n|n'>=delta_nn'

Best,
Daniele