can be determined:

The constants at critical point can be expressed as functions of the parameters a, b:

Using , , the equation of state can be written in the reduced form:

Berthelot and modified Berthelot model

The Berthelot equation (named after D. Berthelot) is very rarely used,

but the modified version is somewhat more accurate

Dieterici model

This model (named after C. Dieterici) fell out of usage in recent years

with parameters a, b. These can be normalized by dividing with