Pressure surface flux virial

Pressure and the surface flux virial construction of the pv operator... 

Equation (22) properly relates the pressure to the virial of the force arising from the surface flux in the momentum density... 

The opening discussion will demonstrate that the definition of pressure is a problem that requires the physics of an open system, classical or quantum. This is an understandable result since the pressure acting on a system is the force exerted per unit area of the surface enclosing the system, the flux in the momentum density per unit area per unit time of the bounding surface. This understanding calls into question the use of the result obtained from the classical virial theorem for an ideal gas to define the pressure acting on a quantum system. 

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