Publication No.69



M. Castillo, C. Velasco, A. Stashans. H atom in CaTiO3: 
structure and electronic properties - Phil. Mag., 2003, 
Vol. 83, p. 1845.

Abstract:
	In the present work we explore effects that an H impurity 
produces upon the geometry and electronic structure of the CaTiO3 
crystal considering cubic and orthorhombic crystallographic lattices 
of the material. A quantum-chemical method based on the Hartree-Fock 
formalism and the periodic large-unit-cell (LUC) model is used 
throughout the work. The analysis of outcomes shows that the 
interstitial H impurity binds to one of the O atoms forming the 
so-called O-H group. At equilibrium, the O-H distances are found to 
be equal to 0.89 and 1.04 � for cubic and orthorhombic lattices 
respectively. Atomic displacements and relaxation energies are 
analyzed comparing obtained results in cubic lattice versus 
orthorhombic one. In the cubic phase the computed relaxation 
energy of vicinity of the O-H group is found to be equal to 1.1 
eV and the atomic displacements generally obey the Coulomb law. 
So, the negatively charged O atoms move outwards the defective 
region by about 0.09 � while the positively charged Ti and Ca 
atoms move towards the defective region by about 0.05 and 0.01 � 
respectively. A similar effect is observed in the orthorhombic 
lattice of CaTiO3 doped with an H atom. It is necessary to mention 
that different O positions in the orthorhombic structure are 
considered for the O-H bond creation. The computed relaxation 
energy of the atomic displacements in this structure is found to 
be equal to 2.3 and 2.1 eV depending on crystallographic type of 
the bonding O atom.




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