G. Casiano Jiménez, L. Sánchez Pacheco, J. Rodríguez Martínez, D. Alej, ro Rasero., and C. Ortega López, A study of the electronic properties of ErB$_{2}$ compound by using the PBE approximation and PBE0 hybrid functional, Rev. Mex. Fís. 60, (2014).