Title: Investigations on Cmc2₁-Si₂P₂X structures and physical properties by first-principles calculations
Author(s):

	R. Yang (School of Physics and Optoelectronic Engineering, Xidian University, Xi'an, Shaanxi 710071, PR China),
	X. Gao (School of Physics and Optoelectronic Engineering, Xidian University, Xi'an, Shaanxi 710071, PR China),
	F. Wu (School of Physics and Optoelectronic Engineering, Xidian University, Xi'an, Shaanxi 710071, PR China),
	Q. Wei (School of Physics and Optoelectronic Engineering, Xidian University, Xi'an, Shaanxi 710071, PR China),
	M. Xue (College of Chemistry and Chemical Engineering, Guangxi University, Nanning, Guangxi 530004, PR China)

The new structures, Cmc2₁-Si₂P₂X (X=S, Se, Te, and Po), are predicted, and their mechanical, electronic and optical properties are investigated with the density functional theory, by first principles calculations. The elastic constants of the four compounds are calculated by the stress-strain method. The calculations of the elastic stability criteria and phonon dispersion spectra imply that they are mechanically and dynamically stable at zero pressure. The mechanical parameters, such as shear moduli G, bulk moduli B, Young's moduli E and Poisson's ratios v are evaluated by the Voigt-Reuss-Hill approach. The Cmc2₁-Si₂P₂X has the largest hardness due to the largest Young's modulus in the four compounds, and it is a covalent crystal. The anisotropies of their mechanical properties are also analyzed. The band structures and densities of states, which are calculated by using HSE06, show that Cmc2₁-Si₂P₂X compounds are indirect bandgap semiconductors, and the values of the band gaps decrease with increasing atomic number from S, Se, Te, to Po. In addition, the longitudinal sound velocity and transverse sound velocity for Cmc2₁-Si₂P₂X have been investigated. The dielectric constant, electron energy loss, refractive index, reflectivity, absorption and conductivity are analyzed to gain the optical properties of Si₂P₂X.

Key words: Cmc2₁-Si₂P₂X (X=S, Se, Te, and Po), first principles, mechanical properties, electronic properties, optical properties

Full text [pdf]

<< List of papers