Wannier function analysis of silicon carbon alloys

Abstract

Maximally localized Wannier functions are the basis of a new technique for resolving ambiguous bonding issues for amorphous materials. Geometrical methods using the Wannier function representation provide an insightful chemical picture of local bonding and hybridization in disordered structures. Central to these methods is the notion of treating the Wannier function centres as a virtual atomic species with a well-defined degree of localization. Using Wannier function methods, we classify and quantify the types of bonding present in a sample of the ternary alloy hydrogenated amorphous silicon carbide, C22Si22H20. In addition to the bonding previously observed for this material, we see three-centre bonding and flipping bonds. We identify a cluster defect in our sample associated with these flipping bonds, and observe a temperature dependence of the bond flipping. This effect may be observable using temperature-dependent Raman spectroscopy.

Real-World Predictions from Ab Initio Molecular Dynamics Simulations

“…The investigation of defect configurations was possible with a novel degree of accuracy through the Wannier approach [86]. Another application of Wannier functions was published by Fitzhenry et al investigating silicon-carbon alloys [87]. In this study the bond structure was resolved by the application of Wannier functions and Fitzhenry et al were able to identify, classify, and quantify the types of bonding present in the alloy.…”

“…In this study the bond structure was resolved by the application of Wannier functions and Fitzhenry et al were able to identify, classify, and quantify the types of bonding present in the alloy. They were able to observe three-center bonding and a temperature dependent flipping of bonds during the simulation [87]. The electron localization function (ELF) was applied to investigate a system of 30 AlCl 3 molecules with one [Emim][Cl] ion pair [89].…”

Maximum Achievable N Content in Atom-by-Atom Growth of Amorphous Si-B-C-N Materials

“…The length of each step was 0.5 ps, leading to a total length of all steps of 2 ps. This frequently used [ 21 , 28 , 30 , 33 , 34 , 35 , 36 , 38 , 39 , 41 ] algorithm captures material formation conditions arising from melting and subsequent rapid quenching of a small volume of a material after an energetic particle impact.…”

“…The presented energy differences ( E - E min where E min corresponds to the lowest-energy density of a given composition) were obtained using time-averaged Kohn–Sham energies collected at the aforementioned temperature of 450 K. For the purpose of a low-temperature comparison of qualitatively similar structures of materials with a band gap, the relevance of time-averaged energy differences is considered to be comparable with that of free energy differences. The bonding statistics, including the number of N 2 molecules ([N 2 ]), were calculated using a representation of pairs of valence electrons by centers of maximally localized Wannier functions (WFCs) [ 38 , 44 ].…”

“…The relationships between composition, density, structure and energy of (pure or hydrogenated) amorphous (Si)-(B)-(C)-(N) materials can be and are often studied by ab initio molecular dynamics (MD) simulations, see the examples for C [ 33 , 34 ], CH x [ 35 ], CN x [ 36 , 37 ], Si-C-H [ 38 ], Si-C-N [ 39 , 40 ] or Si-B-C-N [ 21 , 28 ]. The reliable predictions of local energy minima followed by their characterization in terms of bonding environment of individual atoms or localization of individual electronic states on these atoms allows one to obtain a lot of information not available experimentally.…”