  The collision of two atoms is an intrinsic multi-channel (MC) problem as
becomes especially obvious in the presence of Feshbach resonances. Due to its
complexity, however, single-channel (SC) approximations, which reproduce the
long-range behavior of the open channel, are often applied in calculations. In
this work the complete MC problem is solved numerically for the magnetic
Feshbach resonances (MFRs) in collisions between generic ultracold 6Li and 87Rb
atoms in the ground state and in the presence of a static magnetic field B. The
obtained MC solutions are used to test various existing as well as presently
developed SC approaches. It was found that many aspects even at short
internuclear distances are qualitatively well reflected. This can be used to
investigate molecular processes in the presence of an external trap or in
many-body systems that can be feasibly treated only within the framework of the
SC approximation. The applicability of various SC approximations is tested for
a transition to the absolute vibrational ground state around an MFR. The
conformance of the SC approaches is explained by the two-channel approximation
for the MFR.
