Supervisors info:
Κ. Σιμσερίδης, επίκουρος καθηγητής, τμήμα Φυσικής, ΕΚΠΑ
Σ. Γλένης, επίκουρος καθηγητής, τμήμα Φυσικής, ΕΚΠΑ
Β. Λυκοδήμος, επίκουρος καθηγητής, τμήμα Φυσικής, ΕΚΠΑ
Summary:
We study the electronic structure, including the ionisation energy, the excitation energy, and the transition electric dipole moment of biologically important heterocyclic planar molecules and similar molecules.
We use the Linear Combination of Atomic Orbitals (LCAO) method, taking only
pz atomic orbitals into account. In other words, we use a type of Huckel model [1,2]
but with newer parametrizations [3] and [4]. These parametrizations can be employed to molecules containing carbon, nitrogen, or oxygen atoms with sp2 hybridization. For the diagonal matrix elements, we use empirical parameters, corresponding to carbon, nitrogen with one or two pz electrons and oxygen atoms. For the non-diagonal matrix elements between neighbouring atoms we use [3] the bond-length dependent formula of Harrison [5] (or a variant [4]).
First, we study analytically some small molecules and we compare the analytical
results to the numerical ones of these two parametrizations in order to verify the
validity of the method. In the next chapters we apply this method numerically to
purines, pyrimidines, similar molecules and molecules whose energy gap we have
measured experimentally by taking absorption spectra. Finally, we compare (a) our results to experimental ionisation energies, HOMO-LUMO gaps and transition dipole moments and (b) the two parametrizations to each other.
[1] E. Hückel, Zeitschrift für Physik 70 (1931) 204; 72 (1931) 310; 76 (1932) 628;
83 (1933) 632.
[2] R.B. Woodward and R. Hoffmann, J. Am. Chem. Soc. 87 (1965) 395.
[3] L.G.D. Hawke, G. Kalosakas, and C. Simserides, Mol. Phys. 107 (2009) 1755.
[4] M. Mantela, A. Morphis, M. Tassi, and C. Simserides, Mol. Phys. 114 (2016) 709.
[5] (a) W.A. Harrison, Electronic Structure and the Properties of Solids, Dover,
New York (1989); (b) W.A. Harrison, Elementary Electronic Structure, World Scientific, River Edge, NJ (1999).
Keywords:
electronic structure, ionisation energy, excitation energy, LCAO, Huckel