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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

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Basis set extrapolation in pair natural orbital theories.

Kesha Sorathia¹, David P Tew²

¹Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, GermanyUniversity of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom.

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Summary

Accurate basis set extrapolation requires tight Pair Natural Orbital (PNO) thresholds. Looser thresholds risk false convergence, but PNO truncation level extrapolation offers a viable single-basis set alternative.

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Area of Science:

Computational Chemistry
Quantum Chemistry
Theoretical Chemistry

Background:

Basis set extrapolation is crucial for obtaining accurate molecular properties.
Pair Natural Orbital (PNO) methods are used to reduce computational cost.
Truncation errors in PNOs can impact extrapolation accuracy.

Purpose of the Study:

To benchmark the effect of PNO truncation errors on basis set extrapolation performance.
To assess the reliability of Helgaker's extrapolation method with varying PNO thresholds.
To propose and evaluate an alternative extrapolation approach based on PNO truncation levels.

Main Methods:

Conducted a benchmark study comparing different PNO thresholds.
Applied Helgaker's extrapolation method.
Developed and tested a novel extrapolation approach using PNO truncation levels.

Main Results:

Reliable basis set extrapolation using Helgaker's method requires PNO thresholds of at least 10^-7.
Looser PNO thresholds can lead to false basis set convergence and underestimated errors.
The proposed PNO truncation level extrapolation method demonstrated viability.

Conclusions:

Tight PNO thresholds are essential for accurate basis set extrapolation.
Care must be taken to avoid underestimating errors due to loose PNO thresholds.
PNO truncation level extrapolation offers a promising, single-basis set alternative to hierarchical methods.