Novel low-energy geometries of single, double and triple tellurium atomic helices

A theoretical study of single, double and triple hydrogen-terminated chains of tellurium atoms is presented. Surprisingly, H-terminated single chains with 3 Te atoms per unit cell (as in bulk trigonal Te) are found to be unstable. They relax to regular helical structures with lower energies and smaller twist angles. However, some irregular chains are found to have still lower energies, and compact disordered H-terminated Te chains of mixed chirality are found to have even lower energies. These findings are compared with results of a new systematic study of infinite periodic Te atomic chains. Pairs of H-terminated Te atomic chains are found to form DNA-like double helices with lower energies than compact disordered structures of the two chains. Triplets of H-terminated Te atomic chains are found to form triple helices. The single, double and triple Te helices reported here are beyond the scope of previously studied periodic models with small unit cells.