Accurate Thermochemistry and Kinetics of Molecules with Coupled Motions


Malsch, Laura © Copyright: Lehrstuhl fuer Technische Thermodynamik der RWTH Aachen


Laura Malsch



+49 241 80 95918



Detailed reaction mechanisms are essential for modeling of energy and chemical engineering applications. This holds for fuel design applications as ingnition and combustion processes, but also for networks in polymerization. Often, the parameters of the fundamental chemical mechanisms are not experimentally accessible; nevertheless, they can be computed quantum-mechanically. Therefore one needs to model the electrons in the molecules on the one hand and the nuclei on the other.

  Coupled motion in a methanol dimer. Copyright: LTT

Nuclei move often in a complex coupled manner (cf. Fig. 1) [1]. While methods describing the electrons are very accurate, modeling of the nuclear degrees of freedom turn out to be the bottleneck for the overall accuracy. Widely used models for nuclear motion (like the rigid-rotor harmonic-oscillator approximation) fail to describe coupled motions. Goal of this project is therefore a highly accurate computation of such coupled (and anharmonic) motions at the quantum-mechanical level. By using internal coordinates and some properties of the Jacobian [2], we develop a software that not only computes small systems with benchmark accuracy but also contains approximations for larger systems of technical interest, like biofuels [3] or solvents [4].


Relevant Publications

[1] Muhammad Umer und Kai Leonhard, Ab Initio Calculations of Thermochemical Properties of Methanol Clusters, The Journal of Physical Chemistry A, 2013, volume 117, issue 7, page 1569-1582.

[2] Wassja A. Kopp und Kail Leonhard, General formulation of rovibrational kinetic energy operators and matrix elements in internal bond-angle coordinates using factorized Jacobians, The Journal of Chemical Physics, 2016, volume 145, issue 23, page 234102.

[3] Leif C. Kröger, Malte Döntgen, Dzmitry Firaha, Wassja A. Kopp und Kai Leonhard, Ab initio kinetics predictions for H-atom abstraction from diethoxymethane by hydrogen, methyl, and ethyl radicals and the subsequent unimolecular reactions, Proceedings of the Combustion Institute, In Press, Corrected Proof.

[4] Hannes C. Gottschalk et. al., The furan microsolvation blind challenge for quantum chemical methods: First steps, The Journal of Chemical Physics, 2018, volume 148, issue 1, page 014301.


Project Details


Our research area on molecules with coupled motions comprises currently three projects that are operated by three researchers:

  • In the project „Ab initio Thermochemistry and Kinetics of Molecules with Coupled Large-Amplitude Motions“, funded by DFG, the mathematical foundations of exact and approximate operators are expored and implemented into a software.
  • In the project "High-accuracy ab initio rate constants for key reactions in bio-hybrid fuel combustion“, funded by the Cluster of Excellence "Fuel Science Center", the description of reaction coordinates (and the orthogonal degrees of freedom in transition states) is investigated.
  • In the project „Large amplitude motions (Work Package 4)”, funded by the European Commission in EID "AutoChemo", semi-classical phase-space integration is used to determine strongly coupled degrees of freedom. The project focuses on the reduction of the coupled space and of the computational effort.