What is the exact structure of the AlB2-like polymorph of the CaSi2 compound?

A new high pressure structure of the CaSi2 compound is predicted from first-principles calculations. It corresponds to the KHg2-type which is a slightly distorted derivative of the AlB2-type. Several indications suggest that it is likely the true structure of the superconducting high pressure polymorph of the CaSi2 compound commonly reported as AlB2-like polymorph.

► A new polymorph of the CaSi2 compound is predicted.
► The new structure is likely the true structure of the AlB2-like polymorph.
► Structural and vibrational properties are investigated.