First-principles study on Ca8Cn (n⩽12) and CamC12 (m⩽8) metal carbides

We performed an extensive structure optimization for small Ca8Cn (n⩽12) and CamC12 (m⩽8) clusters by using density functional theory. The structure would gain CaC2 bulk characters for Ca8Cn with n⩾7 and CamC12 with m⩾6, respectively. Two cage-like structures were found and their structural stability was evaluated by molecular dynamics simulations. The Ca 4s valence electrons are donated to the π orbitals of dicarbon and part of the donated electrons is back donated to the Ca 3d split orbitals. Both Ca and C atoms contribute to the magnetic properties. The net charge on Ca analyzed with Bader technique is about +1.4e.