**Principal Investigator**
Michael A. Collins **Project** s01

Research School of Chemistry **Machine** VP

**Co-Investigators:** Meredith
J. T. Jordan and Keiran C. Thompson

Research School of Chemistry

**Molecular Potential Energy Surfaces by Interpolation**

Chemical reactions are simply the combination or
fragmentation of groups of atoms whose movement is governed by
the molecular potential energy surface. We have developed a new
method for constructing such a surface from *ab initiio*
quantum chemistry calculations, so that the dynamics of chemical
reactions can be studied and understood.

**What are the basic questions addressed?**

How efficiently can we construct a molecular potential energy surface (PES) by interpolation of local Taylor expansions of the surface? How can the process be optimised?

**What are the results to date and future of the
work?**

Truncating the local Taylor expansions at second
order is computationally most efficient, while we have also shown
that if the *ab initio* calculation of third order derivatives
of the electronic energy can be improved in efficiency, then third
order expansions should prove to be superior in accuracy and computational
efficiency. The *ab initio* calculation of a surface (at
the Hartree-Fock level of theory) for the OH + H2 Æ
H2O + H reaction has been accomplished. Further development of
the methodology is required for applications to larger systems.

**What computational techniques are used and why
is a supercomputer required?**

Two aspects of this project benefit from a supercomputing environment: ab initio quantum chemistry calculations and the use of classical trajectories in building the surface and evaluating the dynamics.

**Publications**

*Convergence of molecular potential energy surfaces
by interpolation: application to the OH + H 2 Æ
H2O + H reaction*. M. J. T. Jordan,
K. C. Thompson and M. A. Collins, Journal of Chemical Physics,

*The utility of higher order derivatives in constructing
molecular potential energy surfaces by interpolation,*
M. J. T. Jordan,. K. C. Thompson and M. A. Collins, Journal of
Chemical Physics, **103**, 9669 (1995).