  Correlating 3D arrangements of atoms and defects with material properties and
functionality forms the core of several scientific disciplines. Here, we
determined the 3D coordinates of 6,569 iron and 16,627 platinum atoms in a
model iron-platinum nanoparticle system to correlate 3D atomic arrangements and
chemical order/disorder with material properties at the single-atom level. We
identified rich structural variety and chemical order/disorder including 3D
atomic composition, grain boundaries, anti-phase boundaries, anti-site point
defects and swap defects. We show for the first time that experimentally
measured 3D atomic coordinates and chemical species with 22 pm precision can be
used as direct input for first-principles calculations of material properties
such as atomic magnetic moments and local magnetocrystalline anisotropy. This
work not only opens the door to determining 3D atomic arrangements and chemical
order/disorder of a wide range of nanostructured materials with high precision,
but also will transform our understanding of structure-property relationships
at the most fundamental level.
