Efficient calculation of the absolute molecular entropy

Lennard-Jones Centre discussion group seminar by Dr Philipp Pracht from Cambridge University.

The realistic modelling of chemical reactions at finite temperature is a main goal for computational chemistry, where a primary task lies in accurately calculating free energies. Setting aside the issue of solvation and referring to calculations for the isolated molecule, the latter is essentially a problem of efficient computation of molecular entropy. This talk presents an automated composite scheme for the accurate and numerically stable calculation of molecular entropy by efficiently combining DFT and semi-empirical extended tight-binding (xTB) methods [1,2]. Anharmonic effects are included through a modified rigid-rotor-harmonic-oscillator approximation and the Gibbs–Shannon entropy [3] for extensive conformational ensembles, which are generated by a specialized meta-dynamics [4] sampling procedure and extrapolated to completeness. The talk demonstrates the approach on an established benchmark set, where unprecedented root mean square deviations, far better than chemical accuracy, are achieved. Furthermore, the talk addresses possible extensions to the workflow and mentions effects due to the choice of the underlying potential or the environment, for example, by implicit solvation [5].

[1] C. Bannwarth, S. Grimme, et al., WIR Es Comput Mol Sci., 2021, 11, e1493.
[2] P. Pracht, S. Grimme, Chem. Sci., 2021, 12, 6551–6568
[3] D. Suárez, N. Dı́az, WIR Es Comput. Mol. Sci., 2015, 5, 1—26.
[4] P. Pracht, F. Bohle, S. Grimme, PCCP , 2020, 22, 7169—7192
[5] J. Gorges, S. Grimme, A. Hansen, P. Pracht, PCCP , 2022, 24, 12249-12259.

The seminar was held on 30th January 2023.

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