This paper studies first-principles plane-wave pseudopotential based on density functional theory of hydrogen vacancy,metal impurity,impurity-vacancy complex in LiNH 2,a promising material for hydrogen storage.It finds easy formation of H vacancy in the form of impurity-vacancy complex,and the rate-limiting step to the H diffusion.Based on the analysis of the density of states,it finds that the improvement of the dehydrogenating kinetics of LiNH 2 by Ti catalysts and Mg substitution is due to the weak bonding of N-H and the new system metal-like,which makes H atom diffuse easily.The mulliken overlap population analysis shows that H vacancy leads to the H local diffusion,whereas impurity-vacancy complexes result from H nonlocal diffusion,which plays a dominant role in the process of dehydrogenation reaction of LiNH 2.
The surface segregation of La and its effect on the oxygen adsorption on a Mg(0001)surface for a coverageΘ=0.25 monolayer were performed by using first-principles calculations.The calculated results showed that La atoms preferred occupying surface sites to the bulk sites,which suggested the La surface segregation.When oxygen atoms adsorbed on a pure or La alloyed Mg(0001)surface,certain amount of heat would release,and La alloying made the heat released less,which might increase the ignition point of Mg alloy.Both Mg and La had strong atomic affinity with oxygen,so the oxidation film of Mg-La alloys consisted of MgO,La2O3.The denser La2O3 turned oxide film into fine and close structure,and prevented oxygen from passing through the oxidation film.The La-O covalent bonding could explain why La2O3 was compact,and resulted in good ignition-proof of Mg-La alloys.
As the era of nanoelectronics is dawning,CNT(carbon nanotube),a one-dimensional nano material with outstanding properties and performances,has aroused wide attention.In order to study its optical and electrical properties,this paper has researched the influence of tension-twisting deformation,defects,and mixed type on the electronic structure and optical properties of the armchair carbon nanotube superlattices doped cyclic alternately with B and N by using the first-principle method.Our findings show that if tension-twisting deformation is conducted,then the geometric structure,bond length,binding energy,band gap and optical properties of B,N doped carbon nanotube superlattices with defects and mixed type will be influenced.As the degree of exerted tension-twisting deformation increases,B,N doped carbon nanotube superlattices become less stable,and B,N doped carbon nanotube superlattices with defects are more stable than that with exerted tension-twisting deformations.Proper tension-twisting deformation can adjust the energy gap of the system;defects can only reduce the energy gap,enhancing the system metallicity;while the mixed type of 5%tension,twisting angle of 15° and atomic defects will significantly increase the energy gap of the system.From the perspective of optical properties,doped carbon nanotubes may transform the system from metallicity into semi-conductivity.
