As we shall see below, simulations based on internal energies from DFT tend to overestimate the stability of the ground state structure. However, besides configurational entropy that we will model below with our MC model, vibrational entropy will also contribute to the energetics at elevated temperatures. Combining configurational and vibrational entropic contributions has also previously been shown to be important for accurate predictions of alloy stability. In Fig. , the phonon dispersion and density-of-states of the ground state structure is shown. The vibrational degrees of freedom give rise to vibrational entropy, or more conveniently expressed as vibrational free energy as in Eq. 2. Fig. shows the relative free energy between the ground state and a set of metastable structures that are used in the model construction. It is evident that all metastable structures are stabilised compared to the ground state at increasing temperatures, with one metastable state even becoming the thermodynamic ground state above ∼900 K. This shows that vibrational entropy contributes significantly to phase transitions in hybrid organic-inorganic materials as it has been suggested in previous reports. Fitting the model for the relative free energy given in Eq. 3 at each temperature in 100 K intervals, give rise to predicted energies shown in Fig. . As it is computationally expensive to calculate the vibrational free energies for all training structures, we instead use this surrogate model to estimate the relative free energy for all other structures, which in turn is used to fit a new model Hamiltonian at each temperature, with the model quality indicated in Fig. for 300 K.