Structure of liquid GeO₂ from a computer simulation model

The structural properties of liquid GeO₂ are investigated by means of molecular dynamics simulation using a pairwise potential. The simulations were performed in the microcanonical ensemble on systems with up to 576 particles prepared at 21 different densities, corresponding to pressures from -2 to 30 GPa, and temperatures of 1500 K and 3000 K. The pair correlation function, coordination number, angular distribution, and both the neutron and x-ray static structure factors are obtained and compared with those of liquid silica. The analysis of these results for the system at zero pressure indicates that in the liquid state the short range order is dominated by the presence of slightly distorted Ge(O_1/2)₄ tetrahedra. These tetrahedra are linked to each other mainly through the corners, with a Ge-O-Ge angle of ≈130°, similar to the amorphous phase. Beyond the basic tetrahedron some order persists, but to less extent than in liquid silica. Simulation of systems at higher densities shows a volume collapse in the pressure-volume curve in the range of 4–8 GPa, suggesting the possibility that a liquid-liquid phase transition occurs, as the one observed in the amorphous phase.