Cage-like structure and charge hollow in the immiscible Cu–Ta system

Ground states of the immiscible Cu–Ta system are investigated by a hybrid approach of first-principles calculation and cluster expansion method. The obtained pairs, triplets, and tetrads cluster interactions show that the closer-packed cluster may not always contribute to stabilize structures. A CuTa7 phase with a cage-like structure is predicted to be stable at ground state. The obtained spatial valence charge density shows that there exists a charge hollow within this cage-like structure, contributing to stabilize CuTa7 phase.