Temperature dependent phonon information can be obtained in several ways. The most popular methods are based on the temperature dependent effective potential (TDEP), self-consistent phonon theory (SCPH), stochastic self-consistent harmonic approximation (SSCHA), and the velocity auto-correlation function from molecular dynamics trajectories. The features of several software packages that employ these approaches are compared in Table . These methods have become accessible thanks to increased computing power, as well as novel methods for efficient force constant extraction, such as those based on compressive sensing. The stabilisation of high temperature phases has been reported based on renormalised phonon dispersion. Temperature dependent phonons are particularly well suited for the description of second order, soft-mode phase transitions, which can be clearly described from the softening of a single phonon mode. Thus, the temperature above which a high temperature (higher symmetry) phase is stable can be predicted from the temperature at which an imaginary mode becomes real. Generally, experimental phase transition temperatures for second-order phase transitions are reproduced with reasonable accuracy using this method, but examples show that care must be taken to include high enough orders of anharmonicity. It is important to note that several anharmonic phonon methods require all phonon frequencies to be real by definition. Thus when predicting phase transition temperatures from these methods care must be taken to evaluate the frequency as a function of temperature well above the transition temperature, from which the frequency can be extrapolated to zero. For predictions of global stability, the anharmonic vibrational free energy is required. The first choice is to use the expression for the harmonic free energy from Eq. ( ) with the renormalised phonon frequencies instead of the harmonic ones. This allows for calculation of free energies for phases with dynamic instabilities in their harmonic phonon dispersion. However, importantly, an extra correction term must be included to fulfil the first-order cumulant expansion. Within SCPH, the first-order term including the harmonic contributions with renormalised frequencies is given as 38