Spin-Scaled MP2

Spin-component-scaled MP2 (SCS-MP2) improves upon canonical MP2 by scaling the same-spin (SS) and opposite-spin (OS) correlation contributions separately.

Spin-Scaled MP2 — Water

task: MP2 RHF CC-PVDZ

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

MP2
  Scaling  osss
  OS       1.2
  SS       0.333
  FreezeCore false
END

Notes

  • Scaling osss with OS 1.2, SS 0.333 gives the standard SCS-MP2 correction.
  • Spin-scaled variants: SCS-MP2 (1.2/0.333), SCS-MP2 (1.3/1.0), and SCS-MP2 (1.11/0.0) are all accessible via OS/SS keywords.
  • Frozen-core: use FreezeCore true to correlate only valence electrons.