A Theory of Political Entrenchment

We present the results of anab initio-assisted assessment of melting and subsolidus phase relations in thesystem CaO-SiO2up to high pressure conditions. All solid compounds known to nucleate in the system havebeen treated as purely stoichiometric and the liquid resolved in the framework of a simple polymeric model.Mixing properties of the binary liquid phase are fully described by a single-parameter purely enthalpic chemicalinteraction plus a strain energy contribution. The latter is required to predict liquid immiscibility of SiO2-richliquid compositions at ambient conditions and becomes irrelevant at P > 2 GPa. A detailed survey ofthermodynamic properties of silica polymorphs and calcium oxide and silicates in a broad range of P-Tconditions reveals quite controversial stability relations and melting behavior. First-principles calculations onCaO and SiO2pure liquid components and solid phases (lime and stishovite) have been used, along with a soundassessment offirst- and second-order phase transitions, to reconcile thermochemical data with topologicaldetails of the observed phase diagrams. A physically-consistent coupling between thermodynamic andthermoelastic properties (viz. compressibility and thermal expansion) turns out to be of fundamentalimportance to infer reliable stability relations both at subsolidus and melting conditions. Pressure effects shiftthe composition of the main invariant points in the CaO-SiO2system and also change the melting behavior ofthe CaSiO3metasilicate in a complex manner