Vibrational Partition Functions from Bond Order and Populations Relationships

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Physical Chemistry

Background:

• Harmonic vibrational partition functions are crucial for calculating thermal properties of molecules.
• Traditional methods often require computationally expensive Hessian matrix calculations.
• Accurate thermal energy calculations are essential for understanding chemical reactions and material properties.

Purpose of the Study:

• To introduce a novel method, QBOP (Quantum mechanics from Bond Orders and Populations), for computing harmonic vibrational partition functions.
• To enable approximate calculation of finite temperature thermal effects without performing Hessian calculations.
• To provide a computationally efficient alternative for thermal property predictions in computational chemistry.

Main Methods:

• The QBOP model computes zero-point energies (ZPEs) and net vibrational bond energies using the ZPE-BOP model.
• It then maps these computed values to determine the harmonic vibrational partition function.
• The method integrates traditional approximations for rotational, translational, and electronic partition functions.

Main Results:

• The QBOP method successfully computes harmonic vibrational partition functions.
• It allows for approximate thermal energy calculations without Hessian computations.
• Benchmarking against semiempirical models (AM1, PM6, PM7, XTB-2) shows QBOP-1 yields comparable results.
• The model is parameterized using B3LYP/cc-pVTZ+1d data for first-row elements.

Conclusions:

• The QBOP method offers a novel and efficient pathway for thermal energy calculations.
• It significantly reduces computational cost by avoiding Hessian calculations.
• This advancement can alleviate standard bottlenecks in computational chemistry applications.
• The QBOP model provides a valuable tool for predicting molecular thermal properties.