||Prof. Attila Csaszar,|
Eotvos University, Department of Theoretical Chemistry
Up until now the discipline of molecular spectroscopy has been experimentally driven. However, the rapid development of computers has led to a situation where the dream of obtaining complete, accurate solutions to key scientific problems, such as how molecules such as water absorb and emit light, may be achievable entirely theoretically using formal quantum mechanical methods. Achieving this goal would not only be a scientific triumph (see the team's recent publication in the prestigious journal Science) but would allow the solution of problems which are difficult to solve under laboratory conditions: for example, how much light do very hot water molecules absorb in the atmospheres of cool stars and how can one model the much debated greenhouse effect on Earth?
To predict rovibrational spectra, including both line positions and their intensities, to high accuracy it is necessary to solve quantum mechanically two separate (but coupled) sets of equations of motion: those for the electrons and those for the nuclei. In its recent work the Eotvos Lorand University in Budapest (ELTE) team has systematically identified and quantified the contributions of a number of physical effects to potential and dipole surfaces which were until now routinely ignored in such studies: electronic relativistic corrections, failure of the separation between electronic and nuclear motion, and even quantum electrodynamical (QED) effects. Having characterized the various small effects, the only significant remaining error in the high-accuracy calculation of rovibrational spectra is due to difficulties of solving the nonrelativistic electronic structure problem of the valence electrons with high enough accuracy. The particular problem is that standard procedures for representing the correlated motions of the electrons are only slowly convergent. The ELTE team has been working on methodological developments involving the so-called r12 techniques to aid the convergence of the electronic structure calculations. Recently the ELTE team has also been involved in developing new nearly variational techniques for the solution of the nuclear motion problem based on the discrete variable representation (DVR).
The present proposal is for collaboration between several teams consisting of experimentalists and theoreticians. The expertise provided by the ELTE team makes their contribution to the proposed collaboration a very natural one. In particular, the ELTE team has been working on extrapolation procedures that should lead to a major improvement in the accuracy of the electronic structure calculations. Several of the participating groups have already collaborated very successfully on what can be seen as a series of preliminary studies to the present proposal.
List of publications
1. O.L.Polyansky, A.G.Csaszar, S.V.Shirin, N.F.Zobov, P.Barletta, J.Tennyson, D.W.Schwenke, P.J.Knowles, High accuracy ab initio rotation-vibration transitions of water, Science, 299, 539-542 (2003).
2. G.Tarczay, A.G.Csaszar, W.Klopper, H.M. Quiney, Anatomy of Relativistic Energy Corrections in Light Molecular Systems, Molecular Physics, (Invited Paper) 99, 1769-1794 (2001).
3. A.G.Csaszar, G.Tarczay, M.L.Leininger, O.L.Polyansky, J.Tennyson, W.D.Allen, Dream or Reality: Complete Basis Set Full Configuration Interaction Potential Energy Hypersurfaces, in Spectroscopy from Space, edited by J.Demaison, K.Sarka, E.A.Cohen (Kluwer, Dordrecht, 2001), pp.317-339.
4. A.G.Csaszar, W.D.Allen, Y.Yamaguchi, H.F.Schaefer III, Ab Initio Determination of Accurate Potential Energy Hypersurfaces for the Ground Electronic States of Molecules, in Computational Molecular Spectroscopy, 2000, eds. P. Jensen and P. R. Bunker, Wiley: New York.
5. A.G.Csaszar, J.S.Kain, O.L.Polyansky, N.F.Zobov, and J. Tennyson, Relativistic Correction to the Potential Energy Surface and Vibration-Rotation Levels of Water, Chemical Physics Letters, 293, 317-323 (1998).