1. Conclusion By using the first principles calculations, the hydrogen storage on graphyne have been studied. Hydrogen gravimetric capacity would be up to 20%, but the binding energy is only 0.085eV, it is slightly smaller than the optimal adsorption energy for H 2 (0.1 ∼ 0.2 eV∕H 2 ). The binding energy per H 2 increases from 0.08eV to 0.27eV in the presence of an electric field of 0.004 a.u., and the corresponding gravimetric capacity is about 11.1 wt%. The mechanism is being investigated. References [1] Bhatia SK and Myers AL, Langmuir 22,1688–1700 (2006). [2] J. Zhou, Q. Wang, Q. Sun, P. Jena, and X. S. Chen, PNAS 107, 2801–2806 (2010). [3]GX Li, YL Li, HB Liu, YB Guo, YJ Li and DB Zhu, Chemical Communications, 46,3256-3258 (2010). Hydrogen storage on graphyne Y. F. Pan( 潘燕飞 ) and Z. Q. Yang ( 杨中芹 ) Department of Physics, Fudan University, Shanghai 200433, China Introduction With the development of industry, the demands for energy have increased rapidly. But the traditional energy source, fossil fuels are leading to many problems, including environmental pollution and limited energy supply. Green energy sources are urgent to be developed. One promising alternative to fossil fuels is hydrogen. Nanostructured materials offer a host of promising routes for hydrogen storage due to the large effective surface area and the small volume. Two requirements need to be satisfied for the potential applications of hydrogen storage. First, the USA Department of Energy (DOE) has set a hydrogen gravimetric capacity target of 6 wt % by 2010, and 9 wt% by 2015, in the perspective materials for industrial usage. Second, the desirable adsorption energy is about 0.1~0.2 eV per H 2 [1,2]. Recently the first successful synthesis of thin films of graphdiyne (networks of combinations of sp 2 and sp hybridized carbons) was achieved on copper substrates via a cross-coupling reaction using hexaethynylbenzene[3]. Method and Models Our Calculation were performed by using the density functional theory within the local density approximation as implemented in the VASP package in the absence of electric field, and Dmol3 in the presence of electric fields. The plane wave cutoff energy was set to 450.0eV. The convergence thresholds for energy and force were 10 -5 eV and 0.01eV/Å, respectively. Fig. 6 The binding energy per H 2 in which system a layer H 2 are adsorbed on graphyne. When the electric field applied on the system in which a layer H 2 are adsorbed on graphyne, the binding energy per H 2 increases from 0.08eV to 0.27eV in the presence of an electric field of 0.004 a.u. (as shown in Fig.6), and the corresponding gravimetric capacity is about 11.1 wt%. The saltus on 0.001 a.u. is due to the change of the geometry. we focus on the capacity of hydrogen storage on graghyne and the effect of the electric field on the hydrogen storage. The geometry for graghyne are showed in Fig. 1. The structure along a and b directions are periodic. Two adjacent graphyne sheets are separated by at least 20 Å to avoid interactions between each other. A B O Fig. 1 The geometric illustration for graphyne. The gray balls are carbons. The blue frame is the unit cell. The adsorption sites are marked with red stars. Results and Discussion As shown in Fig.1, all possible adsorption sites have been considered. For each site, various initial orientations of the H 2 molecule have been studied. Comparing the binding energies of all adsorption sites, we found the favorite adsorption site is hollow site, and the H 2 are perpendicular to the AB plane. The binding energy of hollow site in the largest hole is about 0.11eV/H 2, and the hollow site in benzene is about 0.10eV/H 2. Fig. 2 The band structure of Graphyne. It’s a semiconductor with a band gap of about 0.42eV. Fig. 3 We found the hydrogen gravimetric capacity could reach up to 20 wt%, as shown in Fig. 3, H 2 could be adsorbed on both sites of graphyne. The corresponding binding energy is about 0.085 eV/H 2. It’s slightly smaller than the optimal binding energy. Fig. 5 The distance between H 2 and graphyne (a), and the binding energy per H 2 in which system only one H2 adsorbed above the honeycomb-like hexagon. Fig. 4 The geometric structure of one H 2 adsorbed on graphyne perpendicular to the AB plane. To enhance the binding energy, we applied electric fields. With the electric field increased, the distance between H 2 and graphyne decreased, and the binding energy increased.