Fig. 4
From: Alkali-metal-adsorbed g-GaN monolayer: ultralow work functions and optical properties
The charge-density difference for alkali-metal-adsorbed g-GaN. a g-GaN/Li, b g-GaN/Na, c g-GaN/K, d g-GaN/Rb, e g-GaN/Cs.The magenta and cyan regions denote the gain and loss of electrons, respectively. The value of the isosurface is set to 0.002 e/Å3