Physical meaning of (negative) pressure in molecular dynamics simulations
Looks fine. 2. I'd phrase that more generally as the simulation volume would tend to expand. 3. But can only do so if the ensemble permits it (pressure can be negative in NVT).


The fluctuations are a consequence of making an observation of a macroscopic quantity over small numbers of degrees of freedom, or time. See http://www.gromacs.org/Documentation/Terminology/Pressure