Evolution of supersonic 2-crowdion clusters in a 3D Morse lattice I. A. Shepelev, S. V. Dmitriev and E. A. Korznikova Eur. Phys. J. B, 94 3 (2021) 71 Published online: 24 March 2021 DOI: 10.1140/epjb/s10051-021-00068-0