Born Effective Charges and Infrared Response of LiBC

TL;DR

This study uses density functional linear response theory to calculate optical phonon modes, Born effective charges, and dielectric response in LiBC, providing insights into its infrared properties and potential implications for related materials.

Contribution

It presents detailed first-principles calculations of phonon modes, effective charges, and dielectric properties of LiBC, highlighting anisotropy and differences in effective charges for B and C.

Findings

Raman modes match experimental data well

Born effective charges differ significantly for B and C

Predicted infrared reflectivity spectrum provided

Abstract

Calculations of the zone center optical mode frequencies (including LO-TO splitting), Born effective charges Z$^*_{\alpha\alpha}$ for each atom, dielectric constants $\epsilon_{0}$ and $\epsilon_{\infty}$, and the dielectric response in the infrared, using density functional linear response theory, are reported. Calculated Raman modes are in excellent agreement with experimental values (170 cm$^{-1}$ and 1170 cm$^{-1}$), while it will require better experimental data to clarify the infrared active mode frequencies. The Born effective charges Z$^*_{\alpha \alpha}$ (i) have surprisingly different values for B and C, and (ii) show considerable anisotropy. Relationships between the effective charges and LO-TO splitting are discussed, and the predicted reflectivity in the range 0 -- 1400 cm$^{-1}$ is presented. These results hold possible implications for Li removal in LiBC, and C substition for B in MgB$_2$.