Simplified wave function models in thermochemical protocols based on bond separation reactions.

Area of Science:

• Quantum Chemistry
• Computational Thermochemistry
• Theoretical Chemistry

Background:

• The ATOMIC protocol provides accurate atomization energies and heats of formation.
• Previous models required computationally intensive calculations.
• Simplification is needed for broader applicability.

Purpose of the Study:

• To explore simplifications of the ATOMIC protocol.
• To reduce computational cost while maintaining accuracy.
• To develop new models for thermochemical property prediction.

Main Methods:

• Utilized bond separation reactions within an ab initio framework.
• Investigated basis-set truncations in coupled cluster calculations (CCSD(T)).
• Explored empirical calibration and spin-component scaling at the MP2 level.

Main Results:

• Developed simplified models (B4, B5, B6) with RMS errors of 0.21-0.46 kcal/mol.
• Achieved RMS errors of 1.01 kcal/mol (EMP3) and 0.70 kcal/mol (ECCSD) by avoiding full triples.
• Spin-component scaled MP2 models reduced RMS error by half, comparable to density functionals.

Conclusions:

• Simplified ATOMIC models offer a balance of accuracy and computational efficiency.
• New models provide reliable thermochemical predictions for molecules containing H, C, N, O, and F.
• The study identified potential errors in existing experimental reference data.