VASP Memory Estimate

Question

Is there any way to get a memory estimate for VASP calculations either directly or indirectly (based on some example calculation)? For example, I would like to be able to predict based on my settings how much memory is needed within about a GB per core.

Answer 1

This is difficult to calculate in detail, but the largest memory objects are probably the Kohn-Sham wavefunctions and the pseudopotential projectors (if you're representing them in reciprocal-space). In order to calculate their memory requirements, you need to know the number of:

• Plane-waves, $N_p$

• Bands, $N_b$ (all the bands you're calculating, i.e. including conduction bands)

• k-points, $N_k$

• Spins, $N_s$

• Total pseudopotential projectors, $N_{proj}$

The wavefunction coefficients will be stored as double-precision complex values, meaning 16 bytes each. The total storage for the wavefunction is thus,

RAM for $\psi = 16\times N_p\times N_b\times N_k\times N_s$ bytes;

RAM for projectors $= 16\times N_p\times N_{proj}\times N_k\times$ bytes.

(Assuming that the pseudopotentials are not spin-dependent.)

This is the total storage for each object; as a rough guide, you could divide them by the number of processes to get the memory requirements per process.