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The entropy and enthalpy changes upon absorption determine the equilibrium adsorption states, the adsorption/desorption kinetics, and the surface reaction rates. However, it is difficult to measure experimentally or calculate theoretically the entropy of adsorption state. Hydrogen is considered as the most promising candidate to solve the global energy problems, and the storage by adsorption on light porous solids constitutes a main avenue to research field. An ideal storage system should be able to operate under ambient conditions with high recycling capacity and suitable uptake-release kinetics. The entropy of adsorbed H2 molecules is of great significance for determining the optimum conditions for hydrogen storage and for designing the storage materials. To the best of our knowledge, however, the only report on the entropy of the adsorbed H2 molecules is that adsorbed on alkali-metal exchanged zeolites at temperatures around 100 K. Due to different assumptions of the entropy changes, the values of the optimum enthalpy H reported in the publications cover a wide range. In this paper, the adsorption states, vibrational modes, and the entropies of H2 molecules adsorbed on (MgO)9 and (AlN)12 clusters are studied by using first principal method. The computation is performed by the second-order perturbation theory (MP2) with the triple zeta basis set including polarization functions 6-311G(d, p). The very-tight convergence criterion is used to obtain reliable vibration frequencies. Analysis shows that six vibrational modes of the adsorption complexes can be attributed to the vibration of H2 molecule. For these normal modes, the amplitudes of the displacements of cluster atoms are usually two orders smaller than those of the hydrogen atoms. As the vibrational frequency is inversely proportional to the square root of the mass, the zero-point energy has an important influence on the adsorption energy. The ZPE correction exceeds half of the adsorption energy, and the adsorption on the anions is not stable after including the correction. Under the harmonic approximation, the normal vibration modes are independent, so the entropy of adsorbed H2 molecules can be calculated by using the vibrational partition function based on the vibrational frequencies. The results indicate that the entropy values depend mainly on the two lowest in-phase vibrational frequencies and it is not directly related to the adsorption strength but determined by the shape of the potential energy surface. In a temperature range of 70350 K and at a pressure of 0.1 MPa, there is a good linear correlation between the entropy of adsorbed H2 and the entropy of gas-phase. The entropy of H2 decreases about 10.2R after adsorption.

Hydrogen is considered as a potentially ideal substitution for fossil fuels in the future sustainable energy system because it is an abundant, clean and renewable energy carrier. A safe, efficient and economic storage method is the crucial prerequistite and the biggest challenge for the wide scale use of hydrogen. The nanomaterial is one of the most promising hydrogen storage materials because of its high surface to volume ratio, unique electronic structure and novel chemical and physical properties. It has been demonstrated that pristine nanostructures are not suitable for hydrogen storage, since they interact weakly with hydrogen molecule and their hydrogen storage density is very low. However, the hydrogen storage capacity of the nanostructures can be significantly enhanced through substitutional doping or decoration by metal atoms. Using density functional theory, we investigate the properties of hydrogen adsorption on Li-decorated C24clusters. Results show that the preferred binding site for Li atom is the pentagonal rings. The interaction of Li atoms with the clusters is stronger than that among Li atoms, thus hindering effectively aggregation of Li atoms on the surface of the cluster. The decorated Li atoms are positively charged due to electron transfer from Li to C atoms. When H2 molecules approach Li atoms, they are moderately polarized under the electric field, and adsorbed around the Li atoms in molecular form. Each Li atom in the Li-decorated C24 complexes can adsorb two to three H2 molecules. The H-H bond lengths of the adsorbed H2 molecules are slightly stretched. The average adsorption energies are in the range of 0.08 to 0.13 eV/H2, which are intermediate between physisorption and chemisorption. C24Li6 can hold up to 12 H2 molecules, corresponding to a hydrogen uptake density of 6.8 wt%. This value exceeds the 2020 hydrogen storage target of 5.5 wt% proposed by the U. S. Department of Energy.

With the accurate ab initio method, the adsorption and dissociation process of H2 molecule on Al7- cluster anion are investigated. The stable structures of molecular adsorption and dissociative adsorption are confirmed. The photoelectron spectra of different structures are further analyzed. The calculations indicate that the adsorption of H2 on Al7- is weak physical adsorption with the adsorption energy about 0.02 eV. The investigation of the dissociation process shows that the energy barrier of dissociation is about 0.75 eV. The densities of states of the Al7- cluster and the dissociative adsorption complex Al7H2- are in good agreement with those obtained by the photoelectron spectroscopy. It suggests that H2 can be dissociated when it is absorbed on Al7- anions produced by laser ablation.

(H2O)6 is the smallest water cluster to form three-dimensional(3-D) structure, and there exist a few low-energy isomers. The stability of the isomers and the isomerization process are studied by ab initio calculations. The difference in energy between the ring structure and the most stable prism is 0.31 eV, which is the energy of one hydrogen bond. The isomerization process of water clusters corresponds to the breaking and/or the reforming of hydrogen bonds. For (H2O)6, the isomerization among the low-energy structures involves the breaking or the reforming of only one hydrogen bond, and the energy barriers separating the isomers range from 0.07—0.21 eV.

Possible adsorption structures of H2O on (TiO2)n(n=3—6) clusters were studied by using genetic algorithm combined with empirical potential function. The structures were further optimized using DFT method B3LYP/6-31G**. The results show that H2O molecule is adsorbed on TiO2 clusters through the attachment of oxygen atom to the titanium atom with lower coordination number. Molecular orbitals show that the bond between water and cluster is formed mainly by the 3s3p orbitals of titanium，the orbitals of H2O keep the basic features unchanged but are more delocalized after adsorption. Combined with population analysis and calculation of vibration frequencies，the results show that the O—H bond becomes weaker after H2O is adsorbed on TiO2 clusters.

A single-parent genetic algorithm (SPGA) is developed from the traditional genetic algorithm to optimize cluster structures. Two mutation operators are used to find the global minimum on the potential surface. The algorithm for optimizing the structure of molecule clusters is proposed. Combined with the TIP3P potential energy, the structures of water clusters (H2O)n(n≤14) is studied using SPGA. The stable structures obtained are in complete agreement with the reported results obtained theoretically and experimentally. The calculation results show that SPGA is an efficient and reliable method to find the global minimum structure of molecular clusters.

We have computed the partial cross section ratios of electron capture into excited states to ground state in collisions of proton with He+ and Li++ ions using Oppenheimer Brinkman Kramers and continuum distorted wave methods. Our results show that the cross section ratios obtained by the two different methods are consistent with each other at high energies. Consequently, we propose a simple method to estimate the partial and total cross sections of electron capture by proton from any hydrogen like ions at high energies.