constant density

Dear LAMMPS users ,

I want to calculate T (∂p / ∂T)ρ on my system ! Temperature multiply to [ pressure variation with respect to temperature variation at constant density] .

Which ensemble do you think is suitable for that ?
How can I make the density to be constant in my simulation?

Thanks for your attention.

I forgot to tell you that I use NVT ensemble but I can’t get good results .
because of Pressure fluctuation sometimes (∂p / ∂T)ρ is positive and sometimes negative !


What are you doing in LAMMPS?

Are you performing separate simulations at constant density, or running a single simulation and taking instantaneous values of p and T?

Jackson ,

I run a single simulation and taking instantaneous T and P .

In that case, you are not measuring the thermodynamic quantities T and
P, but rather the statistical mechanical fluctuations delT and delP.
The quantity <delP/delT> probably has some interesting properties, but
this is not the thermodynamic derivative you are looking for. The most
straightforward to get (dP/dT)_rho is to run two or more
*equilibrated* NVT simulations at different values of T and then use
the finite changes in adjacent (<P>,T) points to estimate dP/dT. The
optimal spacing of the points in T is determined by a trade off in
statistical errors in delta<P> and systematic errors due to curvature