SAPT - computing time questions

Dear colleagues,

I intend to calculate the interaction energy between two hexamethyldisiloxane molecules (see below)

My system has 52 atoms, and I intend to calculate SAPT at the levels sSAPT0/jun-cc-pVDZ, SAPT2+/aug-cc-pVDZ and SAPT2+(3)dmp2/aug-cc-pVTZ to obtain the Lennard-Jones parameters for the atoms of this molecule.

Given my little experience in SAPT, could I ask a few questions?

1 - Is calculating the SAPT energy of a system of this size (i.e., 52 atoms) something viable or is the computation time too high? I say this because I would have to calculate the energy for several pairs of hexamethyldisiloxane for my purpose. Did any colleague calculate the energy of a system similar to this size and could share the estimated time spent on the calculation?

2 - What would be a good starting guess for the number of processors that I could use to calculate SAPT for a system of this size (i.e., 52 atoms)?

Thanks in advance.

The system size is routinely accessible with SAPT2+(3) and TZ basis with psi4.
I’d recommend jun-cc-pVTZ instead of the full aug-cc-pVTZ, the heavy augmentation is not needed for accurate results. Especially on the H atoms. This will save a lot of basis functions.

The scaling beyond say 16 threads is not good but still worth it if the node is free. Running multiple SAPT2+(3) on a single node will slow things down because disk writing/reading may limit the calculations.

Difficult to state a time estimate.

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Thanks for reply.

I cited these 3 SAPT methods (sSAPT0/jun-cc-pVDZ, SAPT2+/aug-cc-pVDZ and SAPT2+(3)dmp2/aug-cc-pVTZ) based on this article

I ran these 3 levels of SAPT for methane pairs with 1 processor and the calculations were quick. For SAPT2+(3)dmp2/aug-cc-pVTZ I spent about 5 minutes at each energy point.

One last question: would a system of this size (i.e., 52 atoms) generate temporary files of more than 100 gb?

Many thanks.

It’s possible more than 100 gb are needed. Hard to estimate well.


Thanks for reply.

I tried 3 levels of SAPT (i.e., sSAPT0/jun-cc-pVDZ, SAPT2+/aug-cc-pVDZ and SAPT2+(3)dmp2/aug-cc-pVTZ) for my 52 atom system and only sSAPT0/jun-cc-pVDZ just ran correctly.

The others gave a problem of lack of memory.

I will try to work with sSAPT0/jun-cc-pVDZ.

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