The electronic structure of the zinc-blende (B3) and rock salt (B1) cr
ystal phases of the magnesium sulphide has been studied at the ab init
io periodic Hartree-Fock level. Binding energies, bulk modulus, Mullik
en populations and band structure have been calculated and compared. A
t 0 K and P = 0 the B1 structure is less stable with respect to the B3
one by 0.25 eV. A phase transition B3 --> B1 is calculated to occur a
round 1 GPa.