In statistical thermodynamics, a partition function is an accumulation of distribution functions. Each distribution function describes a special packing and bonding of atoms in a finite three dimensional space, normally called a structure. So the question is, to what size scale, the number of structures is countable at current stage?

Certainly, the combination of atoms is crucial. The most simple physical model is the packing of hard spheres and equivalently interpenetrable soft particles in a finite space, anyone knew the comprehensive collection for the structures? While in the consideration of real stable atoms in the periodic table, is the number of structures within one nanometer sphere/cubic can be uncountable?