Theoretical Study For The Structures Of Al_nCr^0,±1（n=1-13）Cluster And Molecular Hydrogen Dissociation Adsorption On Neutral Clusters

Clusters due to its size effect, showing different chemical andphysical properties from bulk substances, has opened up newavenues for the development of new materials. Along with thecluster size, composition, the variation of the structure of theclusters, the chemical and physical properties change greatly. Theclusters is more ideal catalyst materials because have a largerspecific surface area and bare outer atoms, therefore, the geometryof the clusters has become the key to understand clusters nature,however, it’s difficult to determine the structure of the clusters inthe experimental, in addition, the relative stability of clusters isrelated to the proportion of the content of the clusters in the series,which is obtained by measuring the intensity of the mass peaks inexperimental. Before measurement Mass must after ionization,which leads to the corresponding to the peak intensity is unable todetermine the ion clusters, neutral neutral clusters. The theoretica calculations to make up for this vacancy, the Cluster Researchbecome finer. Because aluminium element content in the earth’scrust is larger, aluminum alloy material is different from the unit ofdifferent material properties and has attracted widespreadattention. Meanwhile, aluminum alloy cluster structure andelectronic properties was also the attention of people. H2energy isconsidered to be the most promising energy in the21st century, butthe H2storage and transportation become human use of hydrogenenergy urgent need to resolve problems, therefore, it’s greatsignificance to design and development a new type of material.Based on the above reasons, in this paper, we design and researchthe chromium doped aluminum cluster structure, properties andadsorption H atoms and H2behavior, expect to provide a theoreticalbasis and guidance for the development of the new materials.Mainly includes the following contents:1．In the Gaussian03package, using the density functional theory（DFT） B3LYP method, Al atoms in6-31g*basis set and Cr atomicpseudopotential basis set LANL2DZ level design and optimizedequilibrium geometrises of the Al_nCr^（0,±1）（n=1-13）（n=1-13） clusters,and obtain the ground state structures those clusters. at the sametime, examine Al_nCr（0,±1）（n=1-13）（n=1-13） variation of thegeometric structure and electronic properties of clusters, the relative stability and clusters increases with the value of n. Energyusing the zero-point energy correction. The research shows that:the Cr atoms in Al_nCr^（0,±1）（n=1-13）（n=1-13） clusters at the surfaceof the clusters for the neutral clusters, these clusters AlCr, Al₂Cr,Al₆Cr, Al₉Cr, Al₁₃Cr lower chemical activity, stability good. Forcationic clusters AlCr, Al3Cr, Al7Cr, Al10Cr, Al12Cr clusters comparedto the same series of other clusters. For anionic clusters, n value iseven when the cluster stability than n value is an odd number ofclusters of good stability, and the stability of the Al₆Cr–is best. Atthe same time, we take a comparison of the value of we calculatedthe Cr2, Al2, AlCr clusters of bond length, average binding energy,vertical ionization energy and the experiment value and theoreticalvalue of the literature,it’s turn out we use the calculation method isreasonable.2. Using the density functional theory （DFT） B3LYP method, Al, Hatoms using6-31g*basis set and Cr atomic pseudopotential basisset LANL2DZ level of H atoms and H2molecules in Al_nCr （n=1-13）on the adsorption behavior of the clusters were examined, theconclusion is as follows: H atom in Al-Cr of bridge site in AlCrH andAl12CrH structure, for Al₂CrH structure H atom added to Al-Al thebridge site, and H atom added on the top of Al in Al_nCrH （n=3-11,13）structure, the H atoms adsorbed on Al3Cr, Al7Cr, Al8Cr, Al11Crclusters emit more energy. H2is easily physically absorbed on thetop Cr atom of Al_nCr （n=1-13） clusters with a side-on orientation rather than an end-on orientation because of the more effectiveorbital overlap in the side-on orientation. he reaction of Al_nCr withH2would produce Al_nCrH2because of large exothermic energychanges and relatively small activation energies especially for Al₂Crand Al7Cr, which might serve as highly efficient and low-costcatalysts for hydrogen dissociation. The conventionally adsorbedconfigurations with two H atoms sitting on the top of oppositing orneighboring Al atoms are found for Al_nCrH2（n=1,3,4,5,6,7,8,11,and13）. One H atom is located at the bridge site and the other H onthe top site is the most favorable chemisorptions site for Al10CrH2and Al12CrH2cluster. The twofold bridge site is identified to be themost favorable chemisorptions site for two hydrogen adsorption onAl₂CrH₂and Al₉CrH₂clusters. Al₃CrH₂, Al₇CrH₂and Al₁₀CrH₂clustersstable than other clusters in the Al_nCrH₂Series, when the H atomsadded to the Al_nCr clusters, the polarizability have a certain impact.