Coordinates: PubChem 3D conformers (small molecules) and RCSB PDB entries (proteins, nucleic acids). The voxel cloud is a sum of Gaussians per atom, scaled by van der Waals radius, rendered by ray marching a 3D texture, the same technique as volumetric medical imaging; it is a model of where the atoms are, not a measured electron density. The atom view is the opposite: each electron is placed in its subshell and sampled from that orbital's hydrogenic probability density, then the whole cloud is splatted into a volume and ray-marched, so the shape you see is the orbital's rather than the atom's footprint. Radii there are power-compressed and the nucleus is drawn thousands of times too large; at true scale the nucleus is a ten-thousandth of the cloud and neither would be visible.