Out of memory error

[ahmed_biby]

Hi,

I have been trying to run an optical job on a 28 atoms 2D system with a vacuum slab before running the GW job, However, it keeps giving me an "out of memory" error.

I have tried to vary the NCORE from 1 to 64 (the number of cores per node).
I have tried to vary the KPAR from 1 to 64 as well.
I have tried a lot of mixed variations between the NCORE and KPAR
I have tried to use up to 30 nodes each have 64 cores each core has 3.7 GB of memory.

I am using a machine of 3.7 GB/core and 64 cores/node.

The lower level is inaccurate, so I should use this high level of the calculations or the work will be trash.

Please, let me know if I am doing something wrong. Attached are the input files and the OUTCAR file.

Thank you

[pedro_melo]

Dear ahmed_biby,

This seems a supercell calculation. Is that the case? If so, could you try to reduce the number of k-points?

You could you try ALGO=Normal. ALGO=Exact might be too demanding for large systems, since it will try to diagonalise the full Hamiltonian.

Kind regards,
Pedro

[ahmed_biby]

Thank you Pedro. I am using such a high KPOINTS since this is the converged one and I need to make a GW calculation based on the WAVECAR from this calculation.

For Algo= Exact, this is the recommended algo if I want to make a GW calculation from this calculation. Do you know if is accepted to use Algo= All instead?

Thank you

[pedro_melo]

Dear ahmed_biby,

The ALGO=EXACT selects a full diagonalisation of your DFT hamiltonian. This can be very expensive for large systems. I would suggest ALGO=NORMAl, which employs an iterative scheme to compute the non-occupied states. The consequence is that the last empty states are not well converged compared to others. You can avoid using those states by selecting a number of bands in the GW step, NBANDSGW, that is lower than the value you set for NBANDS.

Kind regards,
Pedro

[ahmed_biby]

Dear Pedro,

Thank you so much for your informative reply. I will try this.

Thanks,
Ahmed