  Metal-intercalated iron selenides are a class of superconductors that have
received much attention but are less understood in comparison with their
FeAs-based counterparts. Here, the controversial issues such as Fe vacancy, the
real phase responsible for superconductivity, and lattice stability have been
addressed based on first-principles calculations. New insights into the
distinct features in terms of carrier doping have been revealed.

Superconductivity;Materials Science