Integrator

It would be preferable to have velocity verlet as an integrator. This makes it simpler and more accurate to do pressure control, as the virial and the kinetic energy can be computed at the same point in time without having to take another step further.

I'd put in a vote for having velocity Verlet replace leapfrog Verlet; I don't know of any substantial advantages over velocity verlet. In a vanilla implementation they are essentially equivalent, in that they give exactly the same sequence of configurations. For more complicated variants, Verlet is superior