Physico-Chemical nanomaterials science

Pressure effect on electron spectra of CdSe and CdS
Kashuba A.I.1, Ilchuk H.A.1, Andriyevsky B.2, Petrus R.Y.1, Semkiv I.V.1, Guminilovych R.R.3
1Department of General Physic, Lviv Polytechnic National University, 
Bandera Str., 12, Lviv-79046, Ukraine
E-mail: andrii.i.kashuba@lpnu.ua
2Faculty of Electronics and Computer Sciences, Koszalin University of Technology, Sniadeckich Str., 2, Koszalin 75-453, Poland
3Department of Physical, Analytical and General Chemistry, Lviv Polytechnic National University, St. Yura square., 9, Lviv-79046, Ukraine

Semiconductor compounds AIIBVI have many important applications [1, 2]. In spite of extensive experimental and theoretical studies of these materials, some of their fundamental parameters, e.g. the pressure effect on electron spectra, are still unknown. On the other hand, this information is very important for modeling and developing different optical and electronic devices.
The band structure and related properties of CdSe and CdS olutions have been calculated in a wide pressure range in the framework of the density functional theory (DFT) using CASTEP code. In the present calculations, the generalized gradient approximation (GGA) and the Perdew–Burke–Ernzerhof (PBESOL) exchange-and-correlation functional were utilized. The electrons 4d105s2 for Cd, 3s²3p⁴ for S and 4s24p4 for Se atoms have been taken as the valence ones. The self-consistent convergence of the total energy was taken as 5.0×10-7 eV/atom. Geometry optimization of the lattice parameters and atomic coordinates were performed using the Broyden – Fletcher – Goldfarb – Shanno (BFGS) minimization technique with the maximum ionic Hellmann–Feynman forces within 0.01 eV/Å, the maximum ionic displacement within 5.0×10-4 Å, and the maximum stress within 0.02 GPa. These parameters are sufficiently small to lead to a well-converged total energy of the structures studied.

1.	Dornhaus R. and Nimitz G., Narrow-Gap Semiconductors, Eds. G. Hohler and E. A. Nickisch, Springer, Berlin, 1983.
2.	Faurie J. P., Reno J., and Boukerche M., II–VI semiconductor compounds: New superlattice systems for the future? // J. Crystal Growth.-1985.- 72, N 1–2. P. 111–116.