  Magnet-superconductor hybrid (MSH) systems represent promising platforms to
host Majorana zero modes (MZMs), the elemental building blocks for
fault-tolerant quantum computers. Theoretical description of such MSH
structures is mostly based on simplified models, not accounting for the
complexity of real materials. Here, based on density functional theory, we
derive a superconducting 80-band model to study an MSH system consisting of a
magnetic manganese chain on the s wave superconductor niobium. For a wide range
of values of the superconducting order parameter, the system is a topological
superconductor, with MZMs exhibiting non-universal spatial patterns and a
drastic accumulation of spectral weight on both sides along the magnetic chain.
These side feature states can be explained by an effective model which is
guided by the ab initio results. Performing scanning tunneling spectroscopy
experiments on the same system, we observe a spatial structure in the
low-energy local density of states that is consistent with the theoretical
findings. Our results open a first-principle approach to the discovery of
topological superconductors.
