(1) gem : The main points of treating aqueous species in gem are as follows:

1. Default setting:
   • Default setting wil be made for treating the aqueous ideal solution which consists of the water solvent and the aqueous solvent species.
   
   
2. Specification of activity:
   • Commands re available to specifiy the (logarithmic) activity of aqueous species in an analogous way to the gaseous species for which the partial pressure can be specified. In additio, pH can be also specified as -log a(H+).
   
   
3. Restriction:
   • A new function is introduced to indicate whether the temperature region of calculation is beyond the valid temperature region of respective species. Particularly, this is important for the aqueous species having no high temperature heat capacity.

(2) CHD: The main feature of treating the aqueous species in CHD are given below.

1. Default setting for Pourbaix diagram:
   • The chemical potential diagrams for the aqueous systems are well recognized as the Pourbaix diagrams, and have been widely utilized in various fields so that the present setting is adopted so as to provide the Pourbaix diagrams as default setting.
   • Even so, where the aqueous solutions are not identified from the selected species to be used in construction of the diagrams, such default settings will not be adopted and the normal settings will be validated as nor mal functions in CHD.
   
   
2. Normal diagram, Predominace area diagram, Profile diagram:
   • There can be seen several different diagrams for the well known Pourbaix diagrams. Mostpopular diagrams are those given in the pH-pE(or E/V) plot to indicate what kind of the chemical state is stable for the selected element such as Fe or Mn.
   • Those diagram which exludes the solid or other condensed phase and contains only aqueous species is called the Predominace area diagram.
   • Furthermore, this analysis deals with a mixture consisting of many species so that the profile diagram is also widely utilized to show the concentration or activity of such species as a function of selected variable such as pH.
   
   
3. Pourbaix diagram for Multicomponent systems:
   • The Pourbaix diagrams for the multicomponent systems can be also constructed by following the strategy of generalized chemical potential diagrams and well developped way of representating the stability diagram for the systems containing two target elements such as Fe and S.
   • Normally, the stability regions of the Fe containing compound/species are preferentially selected to be visualized. This can be done in the generalized chemical potential diagrams by adopting the method of unvisualizing the polygons for which do not contain the Fe component. This can be manually operated by changing the transparency of polygons for such items to be shown.

(3) CHD: Other improvements