An ab initio–constant pressure technique is applied to study the pressure-induced phase transition of germanium under uniaxial and hydrostatic stresses. The method successfully reproduces a first order phase transition from the diamond structure to a $\beta$-Sn structure with the application of hydrostatic pressure. The simulations reveal that the uniaxially compressed germanium also undergoes similar phase transition via an intermediate state having a space group of $I{4}_1∕\mathit{amd}$. The transition pressure is significantly lowered for the uniaxial case, and the physical origin of which is associated with bond bending. The computed Poisson ratio of germanium agrees with experiments.

• Received 10 November 2004

DOI:https://doi.org/10.1103/PhysRevB.71.054112