The anharmonicity quantification workflow uses the output of the harmonic phonon workflow (Section 4.1.8) as a starting point to calculate the anharmonicity metric σ A first introduced by Knoop and coworkers. 122 σ A estimates the anharmonicity of a material at a temperature, T , by taking the ratio between the root mean square error of the forces calculated by the harmonic model and the standard deviation of the actual forces in a thermodynamic ensemble average, assuming the mean force is zero. It is defined as