[Mehdi3031]

Hello everybody,
in many cases of openFoam, you can find equation Of State that is modeled as a perfect Fluid such as in:
tutorials/multiphase/compressibleMultiphaseInterFoam/laminar/damBreak4phase/constant/thermophysicalProperties.mercury

thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    transport       const;
    thermo          hConst;
    equationOfState perfectFluid;
    specie          specie;
    energy          sensibleInternalEnergy;
}

mixture
{
    specie
    {
        nMoles      1;
        molWeight   200.59;
    }
    equationOfState
    {
        R           6818;
        rho0        13529;
    }
    thermodynamics
    {
        Cp          139;
        Hf          0;
    }
    transport
    {
        mu          1.522e-3;
        Pr          0.022;
    }
}

or in:
tutorials/multiphase/reactingTwoPhaseEulerFoam/laminar/bubbleColumn/constant/thermophysicalProperties.water

thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    transport       const;
    thermo          hConst;
    equationOfState perfectFluid;
    specie          specie;
    energy          sensibleInternalEnergy;
}

mixture
{
    specie
    {
        nMoles      1;
        molWeight   18;
    }
    equationOfState
    {
        R           3000;
        rho0        1027;
    }
    thermodynamics
    {
        Cp          4195;
        Hf          0;
    }
    transport
    {
        mu          3.645e-4;
        Pr          2.289;
    }
}

There are two parameters "R" and "rho0" that are defined and necessary for perfect liquid model which is defined in OF documentation as following:

I can't figure out what is this value of R which is 3000 for water and 6818 for mercury and how to calculate it for ammonia for example. any Idea?