Compressibility and electronic structure of MgB2 up to 8 GPa

The lattice parameters of MgB2 up to a pressure of 8 GPa were determined using high-resolution x-ray powder diffraction in a diamond anvil cell. The bulk modulus, B-0, was determined to be 151 +/-5 GPa. Both experimental and first-principles calculations indicate nearly isotropic mechanical behavior under pressure. This small anisotropy is in contrast to the two-dimensional nature of the boron p states. The pressure dependence of the density of states at the Fermi level and a reasonable value for the average phonon frequency (omega) account within the context of BCS theory for the reduction of T-c under pressure.