CaSi2, the antibonding-sister of MgB2?

The crystalline and electronic structures of CaSi2 under high-pressure are very similar to those of MgB2. As CaSi2 has two more valence electrons than MgB2, the highest occupied σσ band is bonding for MgB2 and antibonding in CaSi2. We investigated whether high-pressure CaSi2 superconductivity is similar to that in MgB2, with a large electron–phonon coupling between the E2gE2g mode and the in-plane σσ band of the Si sheets. Indeed, this electron–phonon coupling is important, but within the approximations of our calculations (Density Functional Theory, Frozen-Phonon, McMillan Formula), it would not be high enough to account for the superconductivity of high-pressure CaSi2 at Tc∼14K.