Fig. 2.

Geometries of Ca atom with (A) attached and (B) far separated four hydrogen molecules. (C) Optimized geometry and (D) molecular orbital levels of the Ca adsorbed anthracene structure. (E) Same structure as in C, with four adsorbed hydrogen molecules. The isosurface plot of each HOMO state is also illustrated in A, B, and C. Large ivory balls represent Ca. Symbols of other atoms follow the same convention used in Fig. 1. Figure is adapted from the published data in Ref (58), copyrighted by the American Physical Society and Ref (64), with permission from Elsevier.