THEORETICAL AND COMPUTATIONAL CHEMISTRY IN CRETE (TCCC)

Department of Chemistry, University of Crete and Institute of Electronic Structure and Laser FORTH-HELLAS

The group of Theoretical and Computational Chemistry is part of the Physical Chemistry division, and is supported by the Department of Chemistry of the University of Crete (UC), and the Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology, Hellas (FORTH).

UNDERGRADUATE COURSES

Quantum Chemistry (I, II),

Mathematics for chemists, and

Computers and Computational Chemistry.

RESEARCH INTERESTS

Dynamics and spectroscopy of vibrationally highly excited small polyatomic molecules.

Construction of analytical Molecular Potential Energy Surfaces from ab initio calculations and empirical data.

Studies of the structure, dynamics, and thermodynamical properties of atomic and molecular microclusters.

BRIEF ANALYSIS OF CURRENT RESEARCH

The main research effort of the Theoretical and Computational Chemistry Group in Crete is focused in understanding the dynamics of vibrationally excited small polyatomic molecules and in the study of the structures, dynamics and thermodynamics of small and intermediate size atomic and molecular clusters. The driving force for the undertaken projects is our interest to investigate the non-linear mechanical properties of molecular species and the way they manifest themselves in spectroscopy and chemical reactivity.

The molecular Potential Energy Surfaces (PES) in the Born-Oppenheimer approximation are strongly non-linear functions, and thus, the study of dynamics in the classical mechanical approximation requires the application of the theory of Non-Linear Mechanics. This inevitably brings the question of the correspondence between classical and quantum mechanics and related problems of Quantum Chaos. In spite of the fact that there is still no satisfactory theory of Quantum Chaos the good correspondence of classical mechanical stationary objects (Periodic Orbits, Tori, Stable and Unstable Manifolds, Cantori) to the quantum mechanical eigenfunctions found in numerous calculations allows us to apply the systematic techniques of Non-Linear Mechanics to Molecular Dynamics and to extract precious information about the spectroscopy and dynamics of relatively large molecular systems.

Our group has contributed into this field through the development of the Periodic Orbit Method (POM), which is a powerful tool for extracting the dynamics from vibrational spectra and predicting sometimes the existence of exotic states in the molecules which are difficult to foresee with the old spectroscopic models. A review article with recent results of this project is given in [3].

Another field of our research activity is the study of small atomic and molecular clusters. Water clusters were the first systems which attracted our interest not only because of the importance of water in our planet, but also, this species allows us to investigate the dynamics of hydrogen bonding systems. It is well known that clusters bridge the gap between isolated molecules and the macroscopic states. However, clusters may also show unique properties not encountered in large scale bodies. It was a surprise for us to find that small water clusters form stable cubic structures which of course have not been seen in ice [4].

Inert gas aggregates doped with metal cations are prototypes for investigating solvation effects. Molecular beam experiments and laser photodissociation spectroscopy for these systems are carried out with a collaborating experimental group of IESL-FORTH. Molecular dynamics calculations not only reveal the structures of the most stable clusters (magic numbers) which are detected in the mass spectra, but they may also reveal the existence of interesting isomeric forms such as solvated and non-solvated Mg+ in Argon [5]and Paper[6].

For this project it is necessary to construct PESs. This is usually achieved by carrying out accurate ab initio calculations for the small clusters and then employing a model for the larger ones. Thus, this field of Chemical Dynamics brings in collaboration quantum chemists, molecular dynamicists, and experimentalists [7].

PUBLICATIONS:

[1] R. Prosmiti, and S. C. Farantos.
Periodic Orbits, Bifurcation Diagrams and the Spectroscopy of CH System.
J. Chem. Phys., 103:3299, 1995.

[2] H. Ishikawa, R. W. Field, S. C. Farantos, M. Joyeux, J. Koput, C. Beck and R. Schinke.
HCP - CPH Isomerization: Caught in the Act.
Annual Review of Physical Chemistry, 50:443, 1999.

[3] S. C. Farantos.
Exploring Molecular Vibrations with Periodic Orbits.
Int. Rev. Phys. Chem., 15:345, 1996.

[4] A. Vegiri, and S. C. Farantos.
Classical Dynamics of Hydrogen Bonded Systems: Water Clusters.
J. Chem. Phys., 98:4059, 1993.

[5] G. Fanourgakis, and S. C. Farantos.
Potential Functions and Static and Dynamic Properties of and clusters.
J. Phys. Chem., 100:3900, 1996.

[6] G. Fanourgakis, and S. C. Farantos, P. Parneix, and Ph. Brechignac.
Isomerization Processes in Mg^+Ar_{12} cluster: A comparison of anharmonic and harmonic models}
J. Chem. Phys., 106:4954, 1997.

[7] G. C. Fanourgakis, S. C. Farantos, Ch. Luder, M. Velegrakis and S. S. Xantheas.
Photofragmentation Spectra and Structures of Sr⁺Ar_n, n=2-8 Clusters: Experiment and Theory
J. Chem. Phys., 109:108, 1998.

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