Structural transitions in disordered phases of germanium under rapid quenching and pressuring

By means of the tight binding molecular dynamics method with a non-orthogonal basis, the possibility of structural transitions in disordered phases of germanium (Ge) under low and high pressures is investigated. In practice, we carry out three series of simulations; i.e. (1) rapid quenching of liquid Ge (l-Ge) to realise an amorphous phase through the glass transition, (2) increase in the density of amorphous Ge (a-Ge), and (3) increase in the density of l-Ge, the last two series corresponding to the application of pressure. For structural analyses, we calculate (a) static properties such as the two-body distribution function, derivative quantities including the coordination number and bond angle distribution related to three-body correlation; and (b) dynamical properties such as mean-square displacement and diffusion constant. Simple quantities such as the average coordination number and the distribution of the coordination number are shown to provide fundamental information about atomic configurations. The bond-angle distribution function is found to display its value in detecting the transformation of structure especially when the transition takes place between structures of different cohesion type. From these analyses, it is confirmed that, even in disordered systems, the phase transitions in the atomic structures take place when the pressure or temperature is changed rapidly enough over a wide range.