Infrared and Raman spectra of β-BC2N from first principles calculations

We present the study on the infrared and nonresonant Raman spectra of beta-BC2N within the framework of ab initio pseudopotential density functional perturbation theory in a four-atom orthorhombic unit cell. The Raman tensors are calculated from the second-order response of the electronic density matrix with respect to a uniform electric field. Comparison between experiments and calculations for cubic BN is presented to test our method in reproducing all the measured features quantitatively. The LO/TO splitting is well imposed by adding the nonanalytical part deduced from the Born effective charge and macroscopic dielectric constant. Finally, different Raman experiment configurations for beta-BC2N are discussed.