Isotopic effect on thermal physical properties of cubic SiC

Abstract

Using path-integral Monte Carlo (PIMC) and classical Monte Carlo (CMC) simulations in the isothermal–isobaric (NPT) ensemble, we investigate the isotope effect on the thermal properties of the cubic silicon carbide (c-SiC) crystal. At T=50 K, the calculations show that the isotopic substitutions shift up the average vibrational energy and root-mean-square displacements (RMSD) values, with a more significant impact on carbon isotope substitution than the silicon ones. However, the total kinetic to total potential energy ratio suggests that the system behaves harmonically and insensitive to isotopic changes. We also calculated the effect of the quantum contribution on c-SiC crystal, considering the most abundant isotopes. At low temperatures, the c-SiC crystal behaves harmonically, although the C and Si atoms behave anharmonically. The quantum effects increase the lattice constant by almost 0.3%, the average RMSD by 0.0703(4) Å and are responsible for reducing the linear thermal expansion coefficient by about 5.8×10−6 K. The zero-point energy is found about 0.1225(3) eV/atom. A satisfactory agreement between the PIMC values and available theoretical and experimental results are found and discussed.