Tight-Binding Molecular Dynamics Study on the Structural Change of Amorphous Germanium with the Increase of Density

Abstract

The structures of low-density and high-density amorphous germanium (a-Ge) are studied, by using the order-N non-orthogonal tight-binding molecular dynamics method, where N is the number of atoms. The initial amorphous configuration is taken from the results of a glass-transition simulation performed in a separate work, with N ¼ 512. From this initial configuration, we gradually increase the density of the system. In low-density a-Ge, the short-range order (SRO) is characterized essentially by the four-fold configuration although, at lowest densities, the coordination number is smaller than four, thus indicating that quite a few dangling bonds exist. The tetrahedral nature of the SRO in a-Ge is in substance the same as the SRO of a diamond structure which is the low-pressure form of crystalline germanium (c-Ge). On the other hand, the SRO in high-density a-Ge is similar to that of a -Sn structure, the latter being the high-pressure form of c-Ge.

Pressure-induced phase transitions in amorphous and metastable crystalline germanium by Raman scattering, x-ray spectroscopy, andab initiocalculations

“…The glass transitions in Si and Ge under pressure were also studied in two recent works both experimentally 14,15 and through molecular dynamic simulations. 16 The combination of Raman and XAS spectroscopy measurements permitted us to confirm that 8 GPa marks the onset of a polyamorphic transition in our more homogeneous samples. 17 Moreover,Ref.…”

Multiple Amorphous–Amorphous Transitions

“…A tight-binding (TB) MD study to examine the pressure effect on structural and dynamical properties of a-Ge has also been reported [274]. The calculations were performed based on the order-N nonorthogonal TB framework using the Fermi operator expansion method [275].…”

Vibrational properties of amorphous germanium under pressure and its thermal expansion and Grüneisen parameters

“…Both theoretical and experimental studies [21][22][23][24] have provided enough solid evidence for the existence of such a phase transformation from a low-density semiconducting phase to a high density metallic amorphous phase in a-Ge with the application of pressure. In these studies, however, the influence of pressure on the vibrational properties has not been reported.…”