Various Density Functional Theory Study On The Geometry And Binding Energies Of M（H₂）_n⁺（n=1～6）（M=V,Ti）

Recently, along with the gradually in-depth study for hydrogenstorage material, transition metal doped clusters have become ahot research topic. There is a special interaction betweentransition metal and hydrogen molecules, calling as Kubasinteraction. The Kubas interaciton make the transition metal atomeasily adsorbing hydrogen molecules. Moreover, when beingadsorbed, the H-H bond is stretched but not broken. The dopedtransition metal atom can improve the hydrogen storage capacity ofcluster materials. Researchers want to design the hydrogen storagematerial based on Kubas interaction by using theoreticalcalculation method. In recent, many such hydrogen storage clusterswere designed. However, are the general used density fuctionalmethod proper for calculating the Kubas interaction, which still anopen question and need be investiated.At present a lot of DFT methods which suitable for differentsystems were developed. Under the framework of density functionaltheory, we investigate the M(H2)n+(n=1-6)(M=V,Ti) clusters withfifteen density functional methods (DFT) at6-311++g**level. They include Local-density approximation (LDA)(SVWN5),GeneralizedGradient Approximation(GGA)(PW91,PBE) The kinetic energydensity of the generalized gradient approximation (meta-GGA)(M06-L, TPSS),hybrid functional (hyper-GGA)(M06-2X,X3LYP,B3PW91,PBE1PBE、 B3LYP, Long range correction functional(LC-DFT)(CAM-B3LYP, LC-WPBE, WB97X) and the dispersion correctiondensity functional (DFT-D)(WB97X-D, B97-D). The calculated resultsform these DFT methods were compared with the result fromCCSD(T)/aug-cc-PVTZ level and the experimental value. TPSS andCAM-B3LYP offer a reliable approach for optimizing the geometryand determining the H2binding energies for this system. The resultof hybrid functional PBE1PBE also was in agreement with theexperimental result. Our works show that the zero-point energycorrection is very important to envalue the hydrogen binding energy.In most case, the Basis Set Superposition Error (BSSE) is small,except for WB97X-D and B97-D method. The H-H average bondlength and the average distance from V+to the centre of H2molecules are changed with increaseing n.The interactions between Ti+and hydrogen molecules were alsocalculated using the methods mentioned above. The Ti+can adsorbeup to six H2molecules. TPSS and PBE1PBE offer a reliable approachfor optimizing the geometry and determining the H2bindingenergies for this system. Besides, The dispersion correction densityfunctional (B97-D) was in agreement with the experimental result.The results also showed that the zero-point energy correction isvery important to envalue the hydrogen binding energy. In mostcase, the Basis Set Superposition Error (BSSE) is small. Nearly all the DFT method gave same trend for the change of the H-H averagedbond length and the average distance from Ti+to the centre of H2molecules with the increaing n.