# Third-Order M{\\o}ller-Plesset Perturbation Theory Made Useful? Choice of Orbitals and Scaling Greatly Improves Accuracy for Thermochemistry, Kinetics and Intermolecular Interactions

Source: [Third-Order M{\\o}ller-Plesset Perturbation Theory Made Useful? Choice of Orbitals and Scaling Greatly Improves Accuracy for Thermochemistry, Kinetics and Intermolecular Interactions](<https://www.sota2.com/research/paper/68fa3abf1e209131ce8cd392>)

Collection index: [llms.txt](<https://www.sota2.com/research/llms.txt>)

Data updated: 2025-10-25T00:14:45.583Z

Authors: Luke W. Bertels, Joonho Lee, Martin Head-Gordon

Published: 2019-06-06T06:52:32.000Z

## Abstract

We develop and test methods that include second and third-order perturbation theory (MP3) using orbitals obtained from regularized orbital-optimized second-order perturbation theory, $\\kappa$-OOMP2, denoted as MP3:$\\kappa$-OOMP2. Testing MP3:$\\kappa$-OOMP2 shows RMS errors that are 1.7 to 5 times smaller than MP3 across 7 data sets. To do still better, empirical training of the scaling factors for the second- and third-order correlation energies and the regularization parameter on one of those data sets led to an unregularized scaled ($c\_2=1.0$; $c\_3=0.8$) denoted as MP2.8:$\\kappa$-OOMP2. MP2.8:$\\kappa$-OOMP2 yields significant additional improvement over MP3:$\\kappa$-OOMP2 in 4 of 6 test data sets on thermochemistry, kinetics, and noncovalent interactions. Remarkably, these two methods outperform coupled cluster with singles and doubles in 5 of the 7 data sets considered, at greatly reduced cost (no $\\mathcal{O}(N^6)$ iterations).

## Recorded benchmark results

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## Original sources and implementation

[Original paper](<https://arxiv.org/abs/1906.02442>)

[PDF](<https://arxiv.org/pdf/1906.02442.pdf>)