First-principles prediction of layered antiperovskite superconductors A2CNi4 (A = Al, Ga, and Sn)

We theoretically designed and investigated the layered antiperovskite nickel carbides A2CNi4 with different A-site elements by using the first-principles calculation based on density functional theory (DFT). The calculated formation energies for a series of A-site elements show that Al2CNi4, Ga2CNi4, and Sn2CNi4 are stable and can be synthesized at ambient pressure. The elastic properties and electronic band structures were calculated and discussed. Similar to the superconducting MgCNi3, the three stable compounds show the non-magnetic ground states. The density of states at Fermi level N(EF), dominated by Ni-3d electrons, can be comparable with the N(EF) of MgCNi3. The electron and hole bands cross the Fermi level, indicating the multiple-band nature for A2CNi4 (A = Al, Ga, and Sn). Using the McMillan's formula, we approximately estimated the superconducting parameters such as electron-phonon coupling constants λ and superconducting transition temperatures TC. Our present results show that the layered antiperovskite nickel carbides A2CNi4 (A = Al, Ga, and Sn) may be potential weak-coupling superconductors with TC about 5∼7 K.