Building block modeling technique: Application to ternary chalcogenide glasses g-Ge_2As_4Se_4 and g-AsGe_0.8Se_0.8

摘要

Owing to promising optoelectronic and electronic features,1-3chalcogenide glasses have drawn extensive atten tion during the last decade. However, the lack of translational periodicity makes it hard to predict the microscopic structure of these glasses. Experimental results indicate that chemical order is broken and homopolar bonds are observed in chalcogenide glasses.4-6 To further understand the topology and its role in determining optoelectronic and electronic properties, realistic atomistic models of these glasses are required. One possible way to obtain atomic models for glasses is the standard molecular dynamic (MD) "melt and quench" method. This method seems to work when there are fundamental units existing in both liquid and glass. For simple building blocks (BBs) (involving only a few atoms), realistic models are obtained after a long liquid equilibration and a slow quench procedure. However, if the BBs are complex, such as the case in ternary alloys, it sometimes happens that the melt and quench method fails to obtain the correct structure due to the limitation of short simulation times. If a priori information (such as chemical order, correct coordination number, etc.) is unknown for a target material, the melt and quench technique usually starts with random initial configurations and the calculations may be extremely time consuming for large systems. Also, very large cells may be required if the structural order is complex. Our earlier studies indicated that the melt and quench method has difficulties in generating realistic atomic models of Ge-As-Se glasses (more details are discussed in Ref. 7). Thus, in this case, it is of interest to develop a new modeling technique.