  We studied the pressure effects on the electronic and structural properties
of LaOFeAs by first-principles calculations. For the anti-ferromagnetic (AFM)
phase with stripe- like aligned Fe spins, the electronic density of states at
the Fermi level (N (EF)) slightly descends first with increasing applied
pressure, then bounces up with further increasing pressure (or decreasing
volume), and reaches its maximum at ~ 29.2 GPa with the volume ~ 80% of the
ambient pressure value (V0). At this volume (V = 0.8V0), the LaOFeAs crystal
undergoes a structural phase transition from the orthorhombic structure to the
tetragonal one, which is accompanied by the disappearance of the long-ranged
AFM order.
