Evaluation of Density Functionals for Si-O-C-H Molecule Thermochemistry

Area of Science:

• Computational chemistry
• Quantum chemistry
• Materials science

Background:

• Silicon-oxygen-carbon-hydrogen (Si-O-C-H) molecular systems are crucial in various chemical applications.
• Accurate computational data for these systems are essential for predicting their properties and reactivity.
• Existing computational methods require rigorous validation against high-level theoretical benchmarks.

Purpose of the Study:

• To calculate the energies and vibrational frequencies of Si-O-C-H molecules using a high-level theoretical method.
• To evaluate the performance of various density functional theory (DFT) functionals against these benchmark calculations.
• To provide new benchmark data for silicon chemistry.

Main Methods:

• High-level coupled cluster with single and double excitations and a perturbative treatment of triple excitations (CCSD(T)) calculations were performed.
• Density functional theory (DFT) calculations were conducted using nine common functionals and two basis sets.
• Enthalpies of formation, reaction energies, vibrational frequencies, and zero-point energies were computed and compared.

Main Results:

• CCSD(T) results showed excellent agreement with experimental data for enthalpies of formation (1-2 kJ/mol difference).
• M06-2X functional demonstrated the lowest mean absolute error (MAE) for enthalpy of formation.
• SCAN functional yielded the lowest MAE for vibrational frequencies and zero-point energies, while B2GP-PLYP showed minimal errors for reaction energies.

Conclusions:

• PW6B95 functional consistently performed well across various properties of Si-O-C-H molecules.
• DFT methods, particularly M06-2X and SCAN, offer reliable alternatives to high-level CCSD(T) calculations for specific properties.
• The study provides valuable benchmark data for silicon chemistry, aiding future computational studies.