Hi all, I’ve come across an issue with SOS-OMP2 (scaled opposite spin orbital optimized MP2) as implemented in PSI4. In a single point calculation, I get identical energies (OMP2 total energy, scaled_SS energy, scaled_OS energy, SOS-OMP2 total energy, etc) using OMP2 as when I use SOS-OMP2. This i…

Hi. This sounds concerning. First the basics: which psi4 version? Could you post the input (at least the methods part)? The code is located in the the occ and dfocc modules/directories.

Hi Hokru, Version is 1.3.2, and below is the input file. memory 60 GB molecule complex { 0 1 symmetry c1 C -0.000000001327 0.000000002742 -0.566371032553 N 0.000000001055 -0.000000003205 0.602350938174 H 0.000000001134 0.000000011879 -1.6255920…

do_sos true merely sets the values of the current energy and current correlation energy variables to the spin-component scaled values. This has no impact on the orbital optimization whatsoever. Psi4 version is irrelevant. (Use grep -inr "do_sos" . in occ if you want to check for yourself.) The pros…

I can confirm. Identical output for omp2, sos-omp2, scs-omp2 I opened an issue about it on github: https://github.com/psi4/psi4/issues/1751

Psi4 – Open-Source Quantum Chemistry

Scaled opposite spin (SOS) not changing orbital-optimized MP2 (OMP2)