# How do I define the density of system?

Lets' say I have a solid nanomaterial made with N atoms in a simulation box with a volume of V as shown below. In this case, the number density of my material is simply $$\frac{N}{Volume\; of \; occupied\;3D\; space}$$.

but what if I have a nanomaterial with $$N$$ atoms in the same simulation box, but $$N_{1}$$ atoms are in the solid phase and $$N_{2}$$ atoms are in the gas phase $$\left( N_{1} + N_{2} = N \right)$$.

How should I calculate the number density of my material in this case? Do I consider the whole box volume $$V$$? do I have to find an average over the whole material?

• To keep things from getting too long here, I moved the discussion to chat
– Tyberius
Oct 23, 2022 at 3:07