# Isoenthalpic–isobaric ensemble

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Isoenthalpic–isobaric ensemble

The isoenthalpic-isobaric ensemble (constant enthalpy and constant pressure ensemble) is a statistical mechanical ensemble that maintains constant enthalpy $H ,$ and constant pressure $P ,$ applied. It is also called the $NpH$-ensemble, where the number of particles $N ,$ is also kept as a constant. It was developed by physicist H. C. Andersen in 1980. [Andersen, H. C. "Journal of Chemical Physics" 72, 2384-2393 (1980).] The ensemble adds another degree of freedom, which represents the variable volume $V ,$ of a system to which the coordinates of all particles are relative. The volume $V ,$ becomes a dynamical variable with potential energy and kinetic energy given by $PV ,$. [Hwee, Chiang Soo. [http://dynamicslab.mpe.nus.edu.sg/dynamics/project0304/thesis0304/Mechanical%20behavior%20of%20bio-cell%20in%20living%20system%20using%20molecular%20dynamics.pdf "Mechanical behavior of peptides in living systems using molecular dynamics."] ] . The enthalpy $H=E+PV ,$ is a conserved quantity. [ [http://www.fisica.uniud.it/~ercolessi/md/md/node43.html Other Statistical Ensembles] ]

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