Publication No.31



S. Serrano, F. Erazo, A. Stashans. A theoretical study 
of SrTiO3 (110) and (001) surfaces - 7th Conf. Europ. 
Cer. Soc., Brugge (Belgium), 2001.

Abstract:
	A quantum-chemical study of technologically important 
SrTiO3 (001) non-polar and (110) polar surfaces and point 
defects therein is reported in the present work. The computations 
are done using a method developed for periodic systems (crystals) 
and it is based on the Hartree-Fock theory. The atomic 
rearrangement due to the surface creation is obtained for a pure 
strontium titanate by means of the periodic large unit cell (LUC) 
model and using an automated geometry optimisation procedure. As 
it follows from our studies the atomic movements are considerably 
larger in the case of the polar (110) surface leading to the 
relaxation energies equal to 10.2 eV and 12.3 eV for cubic and 
tetragonal lattices, respectively.
	The same technique is employed to study electronic, 
structural and optical properties of the material due to the 
oxygen vacancy and F centre (two electrons in an oxygen vacancy) 
presence. This investigation is done in a comparative manner for 
the tetragonal phase versus cubic phase for both types of 
surfaces. We observe the importance of the Coulomb interaction 
in defining atomic displacements, both their directions and 
magnitude. However, again we have considerably larger values of 
the relaxation energies in the case of the (110) surfaces. Two 
extra electrons due to the F centre are found to be localised 
on the nearest strontium or titanium atoms. The wave functions 
of these electrons are found to be more extended for the 
tetragonal phase. The calculated absorption energies (delta SCF 
method) are in a very good agreement with the available data on 
the fast-electron (4-MeV) irradiation measurements. 




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