(a) The stresses and corresponding volume changes as a function of excitation intensity in rock-salt GST. Here, the negative stress leads to lattice expansions. (b) The stress as a function of the excitation intensity in a series of semiconductors. The inset shows the schematic illustration of inter-band excitation. CB and VB mean the conduction band and valence band, respectively. (c) The projected forces on individual atoms under a 15% excitation in rock-salt GST. The length of arrows indicates the magnitudes. (d) The magnitude of forces on Te atoms with different neighboring vacancies and excitation intensities in rock-salt GST. All panels are reproduced from Ref. [39] by permission of the PCCP Owner Societies.