Abstract
In this paper, the results of the ferroelectric phase transition simulation in barium titanate, by means of ab initio calculations, using FP-LAPW (Full Potential Linearized Augmented Plane Wave) method (Wien97 program) are presented. The paper consists of two parts – in the first one here, the detailed analysis of the calculated energy eigenvalues, potential energy terms, electron populations and electron density distribution together with their changes during gradual crystal cell deformation from regular Fm-3m paraelectric, to P4mm tetragonal ferroelectric barium titanate phase are analyzed. The obtained results are in agreement with our previous crystal-chemical analysis (Tkacz-Śmiech et al. 2003) and show the importance of the charge localization process in region of Ti-O bond along z axis, which leaves the Ti-O bonds lying in xy plane almost intact. The second part of this paper will be focused mainly on the influence of the ferroelectric phase transition on the changes of the band structure, bands character and DOS and their connection with molecular picture of chemical bond in barium titanate crystal.