Head-on and head-off collisions of discrete breathers in two-dimensional anharmonic crystal lattices Andrei A. Kistanov, Sergey V. Dmitriev, Alexander P. Chetverikov and Manuel G. Velarde Eur. Phys. J. B, 87 9 (2014) 211 Published online: 17 September 2014 DOI: 10.1140/epjb/e2014-50343-6