Molecular potential energy surfaces


This project develops and applies methods for constructing, from first principles, the molecular potential energy surface (PES) for molecules undergoing chemical reactions, exchanging energy in collisions, and clustering together. This allows us to calculate how the atoms move during the break-up and formation of new molecules. In this way we can understand the mechanisms and rates of important chemical reactions that take place in the atmosphere, in combustion processes and in inter-stellar space, for example. The study of energy exchange and clustering will ultimately allow us to understand chemical reactions at high pressure and in liquids.


Principal Investigator

Michael Collins
Research School of Chemistry
Australian National University

Project

s01

Facilities Used

SC, VPP, PC, Vizlab

Co-Investigators

Keiran Lim
Centre for Chiral and Molecular Technologies
School of Biological and Chemical Sciences
Deakin University

Ryan Bettens
Alexander Duncan
Christian Evenhuis
Michael Smith
Research School of Chemistry
Australian National University

Donghui Zhang
Department of Computational Science
National University of Singapore

RFCD Codes

250603


Significant Achievements, Anticipated Outcomes and Future Work

Dr Collins, in collaboration with Dr Keiran Lim (Deakin University), developed a program to construct ab initio molecular potential energy surfaces (PES) to describe energy transfer between molecules in gas-phase collisions. The software can now describe the PES as a many body expansion. The code was extended to simulate gas phase collisions in the canonical ensemble for more direct comparison with experimental data. The accuracy of this approach has been proved by comparison with known "model" potentials. Ab initio PESs have now been constructed at the Hartree-Fock level of theory with various basis sets. A series of PES at higher levels of ab initio theory will also be constructed to complete an investigation of the effects of electron correlation and basis set completeness on collisional energy transfer. Collins has written a new version of the program package which is, in principle, capable of constructing the many-body expansion potential energy surfaces for clusters of molecules. Future work will revolve around refining the methodology to provide accurate interactions of many water molecules, so that cooperative hydrogen bonding can be investigated from first principles.

Dr Collins, in collaboration with Assoc. Professor Donghui Zhang, completed and published the PES and quantum reaction dynamics for the H2 + OH Æ H + H2O reaction. The quantum reactive scattering calculations for H + CH4 Æ H2 + CH3 reaction are still in progress (the PES was completed last year). Meanwhile, Collins and Zhang have completed construction of the PES for OH3-, and are preparing publication of this surface and the quantum calculation of the photoelectron spectrum of this anion.

Collins and Mr Michael Smith (PhD student) have completed construction of a PES for the important combustion reaction, H + HCO Æ H2 + CO. Collins and Mr Christian Evenhuis (research assistant funded by APAC) have begun the development of a new program to evaluate the multiple potential energy surfaces and coupling surfaces for reactions involving multiple electronic states. Professor David Yarkony, an expert in this type of electronic structure, visited ANU (partly funded by APAC) to facilitate this new research direction.

 

Computational Techniques Used

The program packages developed in the Collins group use a number of methods. Molecular dynamics simulations and Bayesian statistics are employed along with ab initio quantum chemistry techniques.

 

Publications, Awards and External Funding

M. A. Collins, R. P. A. Bettens, Potential energy surface for the reactions

BeH2 + H BeH + H2, Phys. Chem. Chemical Physics, 1, 1999, 939-945.

R. P. A. Bettens, M. A. Collins, Learning to interpolate molecular potential energy surfaces with confidence: A Bayesian approach, Journal of Chemical Physics, 111, 1999, 816-826.

R. P. A. Bettens, T. A. Hansen, M. A. Collins, Interpolated potential energy surface and reaction dynamics for O(3P) + H3+(1A1’) and OH+(3S-) + H2(1Sg+), Journal of Chemical Physics 111, 1999, 6322-6332.

A. H. Duncan, M. A. Collins, Construction of interpolated potential energy surfaces using constrained dynamics: Application to rotational inelastic scattering, Journal of Chemical Physics 111, 1999, 1346-1353.

M. A. Collins, D. H. Zhang, Application of interpolated potential energy surfaces to quantum reactive scattering, Journal of Chemical Physics, 111, 1999, 9924-9931.

R. P. A. Bettens, M. J. T. Jordan, D. H. Zhang, M. A. Collins, Ab initio potential energy surface for the reactions between H2O and H, Journal of Chemical Physics 112, 2000, 10162-10172.

M. A. Collins, S. Petrie, A. J. Chalk,, L. Radom, Proton-transport catalysis and proton-abstraction reactions: An ab initio dynamical study of X + HOC+ and XH+ + CO (X=Ne, Ar, Kr), Journal of Chemical Physics 112,2000, 6625-6634.

D. H. Zhang, M. A. Collins, S.-Y. Lee, First-principles theory for the H + H2O, D2O reactions, Science, 290,2000, 961-963.

K. Song, M. A. Collins, A classical trajectory study of sym-triazine photodissociation on an interpolated potential energy surface, Chemical Physics Letters, 335,2001, 481-488.

M. Yang, D. H. Zhang, M. A. Collins, S.-Y. Lee, Quantum dynamics on new potential surfaces for the OH + H2 Æ H2O + H reaction, Journal of Chemical Physics, 114,2001, 4759-4762.

M. Yang, D. H. Zhang, M. A. Collins, S.-Y. Lee, Ab initio potential energy surfaces for the reactions OH + H2 H2O + H, Journal of Chemical Physics, 115,2001, 174-178.

R. P. A. Bettens, M. A. Collins, Capture rates for collisions of C (3Pj) and Ge (1S0) with unsaturated hydrocarbons, Journal of Chemical Physics, 114,2001, 10342-10354.

R. O. Fuller, R. P. A. Bettens, M. A. Collins, Interpolated potential energy surface and reaction dynamics for BH+ + H2, Journal of Chemical Physics 114,2001, 10711-10716.