The zero-pressure bulk modulus, pressure derivative of the bulk modulus and their in- and out-of-plane linear values were evaluated. An analysis of the calculated parameters revealed the diversity in bonding interactions. The diboride was characterized by a moderately sizable anisotropy of compressibilities, which was smaller than for cuprates, but larger than for other related diborides. The anisotropic compression was expected to induce different pressure effects on different phonon modes and also to influence the electronic structure at the Fermi energy.

Ab initio Investigation of Mechanical Behaviour of MgB2 Superconductor under Pressure. A.K.M.A.Islam, F.N.Islam, S.Kabir: Journal of Physics - Condensed Matter, 2001, 13, L641-5