Development of Density-Functional Tight-Binding Parameters for the Molecular Dynamics Simulation of Zirconia, Yttria, and Yttria-Stabilized Zirconia

In this work, a set
of density-functional tight-binding (DFTB)
parameters for the Zr–Zr, Zr–O, Y–Y, Y–O,
and Zr–Y interactions was developed for bulk and surface simulations
of ZrO2 (zirconia), Y2O3 (yttria),
and yttria-stabilized zirconia (YSZ) materials. The parameterization
lays the ground work for realistic simulations of zirconia-, yttria-,
and YSZ-based electrolytes in solid oxide fuel cells and YSZ-based
catalysts on long timescales and relevant size scales. The parameterization
was validated for the zirconia and yttria polymorphs observed under
standard conditions based on density functional theory calculations
and experimental data. Additionally, we performed DFTB-based molecular
dynamics (MD) simulations to compute structural and vibrational properties
of these materials. The results show that the parameters can give
a qualitatively correct phase ordering of zirconia, where the tetragonal
phase is more stable than the cubic phase at a lower temperature.
The lattice parameters are only slightly overestimated by 0.05–0.1
Å (2% error), still within the typical accuracy of first-principles
methods. Additionally, the MD results confirm that zirconia and yttria
phases are stable against transformations under standard conditions.
The parameterization also predicts that vibrational spectra are within
the range of 100–1000 cm–1 for zirconia and
100–800 cm–1 for yttria, which is in good
agreement with predictions both from full quantum mechanics and a
recently developed classical force field. To further demonstrate the
advantage of the developed DFTB parameters in terms of computational
resources, we conducted DFTB/MD simulations of the YSZ4 and YS12 models
containing approximately 750 atoms.