Solid-angle based nearest-neighbor algorithm adapted for systems with low coordination number

Nearest-neighbor identification is central to the analysis of local structure in condensed matter systems. The solid-angle-based nearest-neighbor (SANN) algorithm is widely used, offering a parameter-free and computationally efficient alternative to cutoff- or Voronoi-based methods. Unfortunately, however, in systems with low coordination numbers, SANN tends to identify many particles as neighbors that are outside the nearest neighbor shell. Here, we propose a solution to this problem. In particular, we propose a geometric modification, the “inscribed circle modification,” that resolves systematic overcounting in low-coordination lattices without introducing free parameters. We benchmark the modified SANN algorithm against Voronoi and the original SANN algorithm in crystalline, quasicrystalline, and heterogeneous systems and demonstrate that it provides robust and low-cost neighbor identification across both two and three dimensions.