Abstract

This study characterizes the electronic, optical, elastic, and thermal properties of bulk and nanometric Si and ZrO₂ materials through first-principles and theoretical calculations.

The first part of this study presents an investigation of the physical properties, such as electronic and optical, of bulk Si and nanocrystals by using the first-principles method through pseudopotential density functional theory in the ABINIT and CASTEP codes. Various exchange-correlation functionals, including local density approximation (LDA), generalized gradient approximation (GGA), and Heyd–Scuseria–Ernzerh of hybrid functional (HSE06), are used to investigate the effect of different exchange-correlation functionals. For bulk Si, the cohesive and band gap energy values calculated using the hybrid function HSE06 agree with the existing experimental values compared with those calculated using LDA and GGA. The size dependence of both cohesive energy and band gap energy is obtained with HSE06 for Si nanoparticles. The increase in mean bond length leads to the decrease in cohesive energy from (-4.63 eV) for the bulk Si to the (-4.05 eV) for the NPs with diameter 4 nm while it leads to the increase in band gap from 1.153 eV for the bulk value to the 1.333 eV for Si NP at diameter 8 nm in accordance with the decrease in nanosize.

The second part of this work shows an investigation of the effect of the size of low-dimensional materials on mass density and other physical parameters. The general equations for these calculations are established based on the variation of the lattice parameter model with ratio of surface to internal atom ratio. These equations are subsequently applied to zirconia (ZrO₂) nanoparticles and nanofilms in cubic, tetragonal, and monoclinic forms. The mass density is reduced from 6.29 gm.cm^-3 for the bulk state to 2.23 gm.cm^-3 for particles 2 nm in size. These results reveal that the variation in mass density is largely due to the different boundaries and lattice volumes. The calculation results agree well with the available experimental data, particularly for the monoclinic structural form of ZrO₂. The study suggests that the melting temperature, Debye temperature, and cohesive energy are mass density dependence, and all these factors are nanosize dependent.

The effect of size on the bulk modulus is calculated based on the ratio number of surface atoms to that of its internal atoms and is applied to Si. The nanoscale size values of bulk modulus are decreased with the decrease of size. The effect of mass density and melting temperature on bulk modulus are also discussed.

 

posted:12-4-2017