The DFT calculation on the photoexcitation effect of Youngʼs modulus of CdS nanowires. (a) The crystal structure of CdS nanowire. The nanowire is along the c axis and with (0 1 ¯ 10) side surface. (b) Illustration of the charge carrier injection process; under illumination with photon energy larger than the band gap of CdS, electrons will be excited from the valence band to the conduction band. (c) Relative changes of Youngʼs modulus and volume at different injected electron numbers.