Isothermal-isobaric ensemble
= Isothermal-isobaric ensemble
{title2=$NpT$}
{wiki=Isothermal–isobaric_ensemble}
An equilibrium <statistical ensemble> with fixed particle number, <pressure> and <temperature>, allowing <volume> and <energy> to fluctuate. With a temperature-independent volume measure, its joint weight is proportional to $e^{-\beta(E+PV)}$. Its normalization and any temperature-dependent prefactor must be specified when taking thermodynamic derivatives.