Ab initio calculations of free-energy reaction barriers

Autor(en)

Tomas Bucko

Abstrakt

The theoretical description of chemical reactions was until recently limited to a 'static' approach in which important parameters such as the rate constant are deduced from the local topology of the potential energy surface close to minima and saddle points. Such an approach has, however, serious limitations. The growing computational power allows us now to use advanced simulation techniques to determine entropic effects accurately for medium-sized systems at ab initio level. Recently, we have implemented free-energy simulation techniques based on molecular dynamics, in particular on the blue-moon ensemble technique and on metadynamics, in the popular DFT code VASP. In the thermodynamic integration (blue-moon ensemble) technique, the free-energy profile is calculated as the path integral over the restoring forces along a parametrized reaction coordinate. In metadynamics, an image of the free-energy surface is constructed on the fly during the simulation by adding small repulsive Gaussian-shaped hills to the Lagrangian driving the dynamics. The two methods are tested on a simple chemical reaction—the nucleophilic substitution of methyl chloride by a chlorine anion.

Organisation(en)

Computergestützte Materialphysik

Journal

Journal of Physics: Condensed Matter

Band

20

Anzahl der Seiten

9

ISSN

0953-8984

DOI

https://doi.org/10.1088/0953-8984/20/6/064211

Publikationsdatum

2008

Peer-reviewed

Ja

ÖFOS 2012

104017 Physikalische Chemie

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/4f72df75-a1b0-4a63-a173-dfc9b7274c8d