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Random versus Systematic Errors in Reaction Enthalpies Computed Using Semiempirical and Minimal Basis Set Methods.

Jimmy C Kromann1, Alexander Welford1, Anders S Christensen2

  • 1Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark.

ACS Omega
|August 29, 2019
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Summary

The connectivity-based hierarchy (CBH) protocol accurately computes reaction enthalpies using various computational chemistry methods. Fast ab initio and tight-binding density functional theory methods show promising accuracy, while semiempirical methods offer modest improvements.

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Area of Science:

  • Computational Chemistry
  • Quantum Chemistry
  • Physical Chemistry

Background:

  • Accurate computation of reaction enthalpies is crucial for understanding chemical reactions.
  • The connectivity-based hierarchy (CBH) protocol offers a method for calculating reaction enthalpies.
  • Evaluating the performance of different computational methods is essential for selecting appropriate tools.

Purpose of the Study:

  • To assess the accuracy of the connectivity-based hierarchy (CBH) protocol for computing reaction enthalpies.
  • To evaluate the performance of fast ab initio, tight-binding density functional theory (DFT), and semiempirical methods using the CBH protocol.
  • To compare the results obtained from various computational methods against a high-level reference (G4).

Main Methods:

  • The connectivity-based hierarchy (CBH) protocol, specifically the CBH-2 scheme, was applied.
  • A set of 25 diverse chemical reactions was used for testing.
  • Computational methods included PBEh-3c, HF-3c, HF/STO-3G, GFN-xTB, DFTB, DFTB-D3, AM1, PM3, PM6, PM6-DH+, PM6-D2, PM6-D3H+, PM6-D3H4X, PM7, and OM2.
  • Results were benchmarked against the G4 composite method.

Main Results:

  • The CBH-2 scheme demonstrated good accuracy for fast ab initio and tight-binding DFT methods, with mean unsigned errors (MUE) relative to G4 ranging from 1.9 to 4.5 kcal/mol.
  • Semiempirical neglect-of-diatomic-differential-overlap (NDDO)-based methods showed modest accuracy improvements, with MUEs ranging from 4.8 to 6.5 kcal/mol.
  • Outliers were observed for several methods, particularly among the NDDO-based approaches, indicating limitations due to inherent errors in predicted heats of formation.

Conclusions:

  • The connectivity-based hierarchy (CBH) protocol is a viable approach for accurate reaction enthalpy calculations, especially with faster computational methods.
  • Fast ab initio and tight-binding DFT methods show competitive accuracy for reaction enthalpy prediction using the CBH protocol.
  • NDDO-based semiempirical methods, while improved, exhibit limitations in accuracy for reaction enthalpies due to their intrinsic error sources.