Statistical mechanics of nonadditive systems: the unconstrained ensemble

by Ivan Latella (Universitat de Barcelona,)

Wednesday 24 Apr 2024, 16:30 → 17:30 Europe/Rome

The unconstrained ensemble describes completely open systems whose control parameters are the
chemical potential, pressure and temperature. For macroscopic systems with short-range interactions,
thermodynamics prevents the simultaneous use of these intensive variables as control parameters,
because they are not independent and cannot account for the system size. When the range of the
interactions is comparable with the size of the system, however, these variables are not truly intensive
and may become independent, so equilibrium states defined by the values of these parameters may

exist. The independence in this set of variables is directly related to the fact that the system is non-
additive. After reviewing the thermodynamics of non-additive systems, in the talk we consider some

examples of systems with long-range interactions that reach equilibrium under completely open
conditions. We also present a Monte Carlo algorithm to perform simulations in the unconstrained
ensemble and complement the discussion of the examples with simulations.