The main source of entropy in an crystalline solid is usually of vibrational origin, which can to a first approximation be determined using the (quasi-)harmonic approximation to describe the vibrational degrees of freedom. However, when dynamic instabilities are present in the phonon dispersion, which is often the case for high temperature phases, the harmonic approximation breaks down and the vibrational entropy becomes illdefined . In such cases, we must resort to an anharmonic treatment of the phonons. In recent years, significant progress has been made in the modelling of anharmonic lattice vibrations including the temperature dependent e↵ective potential method , stochastic self-consistent harmonic approximation , and self-consistent phonon theory . This has paved the way for modelling of finite temperature phonon dispersions, lattice thermal conductivities, as well as free energy calculations beyond the harmonic approximation .