Electronic band structure and gap formation in CeRhAs

We have performed first-principles band structure calculation for CeRhAs and its isostructural Cc compounds. Calculated insulating and metallic or semimetallic ground states are consistent with recent experimental observations. We discussed projected density of states on Cc 4f \J, J(Z)> states, which is a clue to understand the anisotropic effects to realize the ground state and gap formation. Band gap and pseudogaps are opened mainly due to Ce 4f \5/2, +/- 5/2> states. These states are very sensitive to lattice deformation. Gap formation and structural instability in CeRhAs may be understood by orientations of Cc 4f orbitals.