Born effective charges and infrared response of LiBC

Calculations of the zone-center optical-mode frequencies (including LO-TO splitting), Born effective charges Z(alphaalpha)(*) for each atom, dielectric constants epsilon(0) and epsilon(infinity), 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(alphaalpha)(*) (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 MgB2.