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Updated: Jun 24, 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

Ab initio thermochemistry using optimal-balance models with isodesmic corrections: the ATOMIC protocol.

Dirk Bakowies¹

¹Laboratory of Physical Chemistry, ETH Zürich, CH 8093 Zürich, Switzerland. bakowies@chem-edu.ethz.ch

The Journal of Chemical Physics

|April 17, 2009

Summary

A new computational method, ATOMIC (Ab initio Thermochemistry using Optimal-balance Models with Isodesmic Corrections), accurately calculates molecular atomization energies and enthalpies of formation. This approach balances accuracy and cost for high-level theoretical chemistry predictions.

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Area of Science:

Computational Chemistry
Theoretical Chemistry
Quantum Chemistry

Background:

Accurate calculation of molecular atomization energies and enthalpies of formation is crucial for understanding chemical reactions and properties.
Existing high-level computational methods often face challenges in balancing accuracy with computational cost.

Purpose of the Study:

To introduce ATOMIC (Ab initio Thermochemistry using Optimal-balance Models with Isodesmic Corrections), a novel composite approach for calculating thermochemical properties.
To achieve an optimal balance between accuracy and computational cost in theoretical thermochemistry.
To provide a robust and efficient method for predicting molecular energies.

Main Methods:

Decomposition of coupled-cluster energy into Hartree-Fock, low-order correlation (MP2, CCSD), and connected-triples contributions.
Inclusion of valence-shell and core contributions, with statistical analysis to determine basis-set and extrapolation requirements.
Implementation of Pople's bond-separation reactions within an ab initio framework to provide isodesmic corrections.

Main Results:

The ATOMIC approach offers a hierarchy of three levels (A, B, C) for isodesmically corrected composite models, achieving high accuracy (0.1–1 kcal/mol) in atomization energy reproduction.
Corrections beyond CCSD(T) can be efficiently estimated using a simplified model with bond increments.
Preliminary validation shows ATOMIC performs comparably or slightly better than the G3 approach for enthalpies of formation, without empirical calibration.

Conclusions:

ATOMIC provides an accurate, cost-effective, and non-empirical method for calculating molecular atomization energies and enthalpies of formation.
The method is efficient enough for routine application to molecules with up to 20 non-hydrogen atoms.
ATOMIC represents a significant advancement in theoretical thermochemistry, offering a reliable alternative to existing computational protocols.