Abstract
The crystal structure of orthorhombic black phosphorus under pressure is calculated as a function of volume using the pseudopotential total-energy method. As a result, it is shown that the anomaly of the lattice constants observed experimentally at the density of 17.5Å3/atom is due to an unusual isostructural second order phase transition and its physical origin is attributed the repulsive force effect due to overlap between valence electron charge clouds of neighboring puckered layers.