Calculation of Accurate Thermo Chemical Data for Fluxional Molecules

• Applicant: Professor Dr. Kai Leonhard
• Subject Area: Technical Thermodynamics ; Chemical and Thermal Process Engineering
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 518799413

Thermochemical equilibrium and kinetic data are needed for the design of processes, molecules, and catalysts. In recent decades, improved algorithms and computer power have drastically reduced the uncertainties in the calculations of electronic energies. As a result, for the calculation of free energies of flexible molecules and, consequently, of all their equilibrium and kinetic properties, entropy is now often the largest source of uncertainty. This is because entropy is often still calculated with the rigid-rotor harmonic oscillator (RRHO) model for nuclear motion, even when highly accurate coupled-cluster methods are used to model electronic energies. The group of the PI have developed their own initial model for calculating the free energies of flexible molecules, have implemented an early version of it in software, and have validated it with experimental data for the small molecules for which this early version is practical. The here proposed project aims to solve two major challenges in order to apply the approach to larger, technically relevant molecules and processes: 1) by increasing the efficiency of the Monte Carlo integration step crucial to the approach by developing a new way to distribute sampling budgets under a recursive stratified sampling scheme, which we have derived recently and 2) by partitioning phase space into approximately harmonic degrees of freedom and fully anharmonic degrees of freedom and hybridizing methods to solve each partition to reduce the dimensionality of the problem with minimal loss in overall accuracy. The anticipated result of the project will be a validated method for the accurate calculation of thermochemical data of technically relevant substances that can later be used to design new materials and processes.

• DFG Programme: Research Grants