# Modified Opposite-Spin-Scaled Double-Hybrid Functionals

## TL;DR

This paper explores modified double-hybrid functionals for better accuracy in quantum chemistry calculations, especially for noncovalent interactions.

## Contribution

The study introduces modified opposite-spin-scaled MP2 (MOS-MP2) in double-hybrid functionals and evaluates its performance.

## Key findings

- MOS-double hybrids show better accuracy than SOS-MP2-based hybrids without dispersion correction.
- Noncovalent interaction subsets drive most of the performance improvement.
- D4 dispersion correction reduces the performance gap between MOS- and SOS-MP2-based hybrids.

## Abstract

We investigate the
potential performance improvements of double-hybrid
density functionals by replacing the standard scaled opposite-spin
MP2 (SOS-MP2) with the modified opposite-spin-scaled MP2 (MOS-MP2)
in the nonlocal correlation component. Using the large and diverse
GMTKN55 data set, we find that MOS-double hybrids provide significantly
better accuracy compared to SOS-MP2-based double hybrids when empirical
dispersion correction is not employed. The noncovalent interaction
subsets account for the majority of this improvement. However, when
the D4 dispersion correction is applied, the performance gap between
MOS-MP2- and SOS-MP2-based double hybrids becomes negligible. While
the new methods do not outperform the current state-of-the-art double
hybrid functionals, our study offers valuable insights into the applicability
of distance-dependent MP2 in place of conventional SOS-MP2, as well
as the critical role of empirical dispersion corrections in further
enhancing accuracyinsights that are useful for guiding future
method developments. For nine transition metal sets, dispersion-corrected
spin-component-scaled double hybrids are still significantly better
than any MOS-double hybrid functional.