First-principles investigation of the electronic and lattice vibrational properties of Mg2C

Mg2C, a newly synthesized magnesium carbide under high pressure, is a small band gap semiconductor. A first-principles investigation of the electronic and lattice dynamic properties of Mg2C are presented. We find the electronic band gap of Mg2C decreases slowly with pressure increasing. There are two optical vibrational modes at the Γ point of Mg2C. One is F1u mode, and the other is F2g mode. The former mode is infrared active and the latter one is Raman active. Their vibrational frequencies increase sharply with pressure increasing. Furthermore, we find that Mg2C has large infrared intensity and Raman activity, which indicates that infrared and Raman spectra may play a key role in identifying Mg2C. Moreover, we calculate the dielectric tensor and LO–TO splitting under different pressure and find large LO–TO splitting in the F1u mode of Mg2C. Our calculated results provide extraordinary insights into the infrared and Raman spectra of Mg2C.