Is there a conveniently small unit of volume for talking about molecules? When discussing energy transformations on the molecular scale, we usually use electronvolts as the energy unit. This is handy because chemical bond energies are a few electronvolts in magnitude.
I had an idea to go through some thermodynamic tables and convert them into molecular-scale units (energy in $\mathrm{eV}$, entropy in bits, etc.) in order to get a feel for how chemistry works on the scale of single molecules. However, for talking about volume changes (that is, average volume change per molecule), I can't think of a convenient unit. All of the most commonly used volume units ($\mathrm{\mu L}$ etc.) are far too large, apart from Planck units, which are far too small. Even yoctolitres are a bit on the big side, and I've never heard of anyone tabulating values in $\mathrm{yL}$.
Of course it wouldn't be hard to define a convenient unit, for example by deriving it from the ideal gas law at a standard temperature and pressure. But it would be better to use a unit that people already recognise. So my question is: is there a unit of volume in common use that is of a convenient size for thinking about single molecules? That means, I guess, that it should be between around $10^{-31}$ to $10^{-27}\;\mathrm{m^3}$, and preferably towards the smaller end of that.
 A: There are atomic units, where 
Length is: Bohr radius = 1
Mass is: mass electron = 1
Time is: Bohr period = 1
See above link for a full explanation of the system.
A: Crystallographers mostly talk about the spacings between lattice planes in Ångstroms, as tpg2114 says in a comment.
I have found myself tabulating number densities for different materials in atoms per barn-cm.  This is because the transmission through an absorber with number density $n$, thickness $\ell$, and capture cross section $\sigma$ is 
$$
T = \exp -n\sigma\ell
$$
and I typically have cross sections in barns and care about lengths in centimeters.  A barn is an area unit equal to 100 fm2 = 10-28 m2 = 10-24 cm2.  This is a very small unit of volume, but it's a very long and skinny volume.
I can't remember if I started doing that on my own or if I copied it from someone else, but it was damned useful for doing transmission calculations.  Don't know how appropriate for thermodynamics, though.  Interesting question!
A: A cubic nm contains 33 molecules of water.  The smallest amount of H2O needed to make water, is six molecules, or 0.18 cu. nm.
