where E 0 , V 0 , B 0 and B 0 ʹ are the equilibrium energy, volume, bulk modulus and its first pressure derivative, respectively. (see Table ). In the case of boron phosphide (Fig. ), the intersection of E(V) curves of zinc-blende and qtz phases is observed at V/FU = 15.6 Å, which for zb-BP is equivalent to a reduced volume of 0.67. The corresponding pressure can be calculated by the Murnaghan equation