Economical post-CCSD(T) computational thermochemistry protocol and applications to some aromatic compounds

Area of Science:

• Computational chemistry
• Quantum chemistry
• Thermochemistry

Background:

• Accurate computational thermochemistry requires post-CCSD(T) correlation effects.
• Evaluating the T(3)-(T) term is computationally expensive for larger systems.

Purpose of the Study:

• To develop a cost-effective empirical approximation for the T(3)-(T) term.
• To achieve kilojoules-per-mole accuracy in computational thermochemistry for larger molecules.

Main Methods:

• Developed an empirical approximation for the T(3)-(T) term, independent of experimental data.
• Applied the W3.2lite protocol to various aromatic and aliphatic hydrocarbons.

Main Results:

• The W3.2lite protocol achieves a 95% confidence interval of approximately 0.4 kcal/mol for atomization energies of first-row molecules.
• Successfully applied to hydrocarbons including benzene, fulvene, and bicyclo[1.1.1]pentane.
• Discrepancies between W3.2lite predictions and experimental data for certain molecules suggest potential need for remeasurement.

Conclusions:

• The W3.2lite protocol provides a computationally efficient approach to high-accuracy thermochemistry.
• Empirical approximations can effectively capture crucial post-CCSD(T) correlation effects.
• The protocol's predictions highlight potential experimental inaccuracies, guiding future research efforts.