Isotope effects on the lattice parameter of cubic SiC

TL;DR

This study uses path-integral molecular dynamics to quantify how isotope mass variations affect the lattice parameter of cubic SiC, revealing measurable isotope-dependent lattice differences at 300 K.

Contribution

It provides a nonperturbative, quantum-mechanical analysis of isotope effects on lattice parameters in SiC using PIMD simulations, which is novel.

Findings

Isotope substitution causes measurable changes in lattice parameters.

The effect of carbon isotopes is larger than silicon isotopes.

Results align with quasiharmonic approximation predictions.

Abstract

Path-integral molecular dynamics simulations in the isothermal-isobaric (NPT) ensemble have been carried out to study the dependence of the lattice parameter of 3C-SiC upon isotope mass. This computational method allows a quantitative and nonperturbative study of such anharmonic effect. Atomic nuclei were treated as quantum particles interacting via a tight-binding-type potential. At 300 K, the difference Delta a between lattice parameters of 3C-SiC crystals with 12C and 13C amounts to 2.1 x 10^{-4} A. The effect due to Si isotopes is smaller, and amounts to 3.5 x 10^{-5} A when replacing 28Si by 29Si. Results of the PIMD simulations are interpreted in terms of a quasiharmonic approximation for the lattice vibrations.