Moderate-Cost Ab Initio Thermochemistry with Chemical Accuracy

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate calculation of molecular energies is crucial for understanding chemical phenomena.
• Existing high-accuracy methods can be computationally expensive.
• Development of cost-effective yet reliable computational models is an ongoing challenge.

Purpose of the Study:

• To develop a moderate-cost ab initio composite model chemistry, diet-HEAT-F12.
• To incorporate explicitly correlated coupled-cluster methods and correlation consistent basis sets.
• To reproduce benchmark energy contributions without fitted parameters.

Main Methods:

• Development of the diet-HEAT-F12 model, combining CCSD(T*)(F12) and coupled-cluster methods.
• Inclusion of diagonal Born-Oppenheimer and scalar relativistic corrections.
• Selection of methods and basis sets to mimic benchmark HEAT contributions.

Main Results:

• The diet-HEAT-F12 protocol demonstrated superior error statistics compared to W3X, W3X-L, and W3-F12 models.
• Reliability was validated using the W4-11 dataset and 23 literature atomization energies.
• A method for calculating size-dependent 95% confidence intervals was established.

Conclusions:

• The diet-HEAT-F12 model provides a cost-effective and accurate approach for calculating molecular energies.
• The model achieves high accuracy without relying on fitted parameters.
• It represents a significant advancement in computational chemistry for energy calculations.