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Updated: May 23, 2026

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

Published on: April 8, 2020

Improved correlation energy extrapolation schemes based on local pair natural orbital methods.

Dimitrios G Liakos¹, Frank Neese

¹Max-Planck Institut für Bioanorganische Chemie, Stiftstrasse 32-34, D-45470 Mülheim an der Ruhr, Germany.

The Journal of Physical Chemistry. A

|April 12, 2012

Summary

Accurate quantum chemistry calculations are essential. Replacing MP2 extrapolation with local pair natural orbital coupled-electron pair approximation (LPNO-CEPA/1) in basis set extrapolation schemes offers systematically improved accuracy at minimal additional cost.

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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

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Published on: May 27, 2020

Area of Science:

Computational Quantum Chemistry
Theoretical Chemistry
Ab Initio Methods

Background:

Reaching the basis set limit in correlated post-Hartree-Fock ab initio calculations is computationally challenging.
Basis set extrapolation schemes are commonly used to approximate the complete basis set limit.
Traditional schemes often use coupled cluster theory with single, double, and perturbative triple excitations (CCSD(T)) at the highest level and second-order Møller-Plesset perturbation theory (MP2) for extrapolation.

Purpose of the Study:

To investigate alternative basis set extrapolation schemes beyond the standard MP2 method.
To evaluate the performance of coupled-electron pair approximation (CEPA/1) and its local pair natural orbital variant (LPNO-CEPA/1) in extrapolation schemes.
To provide improved reference interaction energies for the S66 dataset.

Main Methods:

Development and application of basis set extrapolation schemes using LPNO-CEPA/1 instead of MP2.
Comparison of LPNO-CEPA/1 extrapolation with canonical CEPA/1 and MP2-based extrapolation.
Calculation of interaction energies for the S66 dataset using the proposed CCSD(T)/LPNO-CEPA/1 extrapolation scheme.

Main Results:

The MP2 method's apparent accuracy is attributed to error cancellation; LPNO-CEPA/1 provides systematically more accurate results.
LPNO-CEPA/1 exhibits negligible errors compared to canonical CEPA/1.
Basis set extrapolation using LPNO-CEPA/1 significantly reduces errors in total energies and energy differences, yielding new reference values for S66 interaction energies with deviations up to 0.3 kcal/mol.

Conclusions:

Replacing MP2 with LPNO-CEPA/1 in basis set extrapolation schemes offers a more accurate and computationally efficient approach.
The LPNO-CEPA/1 method combined with basis set extrapolation provides highly accurate energy values.
The proposed CCSD(T)/LPNO-CEPA/1 extrapolation scheme yields reliable reference data for molecular interaction energies.