There are methods to choose the appropriate thermodynamic models; see Ref. 78. This choice depends on the nature of the property, composition of the mixture, operational pressure and temperature, and availability of model’s parameters for the simulation; see Ref. 79. Below is a decision tree that can be used as a guide for choosing the thermodynamic model:

It is possible to manually modify the species properties, such as parameters and temperature-dependent functions, in the database file. In the same manner, you can manually add new species that do not exist in the database. To do this, right-click a system node under Thermodynamics and select Export thermodynamic system. Save the thermodynamic system as an xml file.

All the parameters and temperature-dependent properties are saved inside a <Compound CompID="name"></Compound> block. For example, to edit the acentric factor of methane from 0.01141 to 0.2 perform the following steps

Here Tlb and Tub defines the lower and upper bound for a temperature range, and a1 to a4 are the corresponding coefficients for a cubic polynomial as f(T) = a0 + a1T+ a2T2+ a3T3 fitted for that range. Multiple sequential ranges can be added by appending temperature ranges and coefficient sets. The <Data></Data> block can be used to input data points directly.