Theoretical Study Of The Diffusion Behavior Of Helium Atoms In The Metal Vanadium, Titanium

The diffusion behaviors of single helium atom in perfect crystal of V and Ti have been studied. The system of combined helium atom and metals has been calculated using the three quantum methods of effective medium theory (EMT), CASTEP and Dmo13. The stability of system can be determined from the variety of energy and volume. The most possible diffusion path for helium atom in interstitial site of metals can be also forecasted. The mechanism of the interaction between helium atom and metals was described by atomic population, overlap population, the band structure and density of state.The results of EMT proved that the embedding energy for helium atom in vanadium was lower in tetrahedral interstitial site than in octahedron interstitial site which value was 4.30eV, the diffusion barrier between interstitial sites was 0.003eV. The most possible diffusion path was along these points which were (1,1/4,1/2, (1,1/2,1/2) (1,3/4,1/2) . Contrary to the situation of V, the embedding energy for helium atom in titanium was lower in octahedron interstitial site than in tetrahedral interstitial site which value is 2.98eV, the diffusion barrier between interstitial sites was 0.3550eV. The most possible diffusion path was along the channel combined of the larger octahedron interstitial site (o2) and the near larger tetrahedral interstitial site (tl).The results of CASTEP proved that the embedding energy of V-He(t) (the system which helium atom embedded in tetrahedral interstitial site of V) was lower than V-He(o) (the system which helium atom embedded in octahedron interstitial site of V). The single point energy of V-He(t) was -7976.5111eV, and the V-He(o) was -7975.7495. The helium atom was more stability in tetrahedral interstitial site than in octahedron interstitial site. When V/He=4:l, the swelling of cell is small, The change of V-He(t) was smaller than V-He(o). The population analysis proved the interaction between helium atom and V was electrovalent bond. The helium had the stronger attractive to the vanadium atom which was in lattice site. So the vanadium was ease to form the vacancy in lattice site. The embedding energy of Ti-He(o2) was the lowest of four systems of Ti-He(two octahedron interstitial sites and two tetrahedral sites) which value is -6481.4287eV. The following is Ti-He(tl) which value is -6480.3 876eV. Ti-He(o2) had the more stable structure of four systems of Ti-He. The variety of volume before and after Geometry optimization proves this result. The population analysis also proves the interaction between helium atom and Ti was electrovalent bond. The helium atom had the stronger attractive to the titanium atom which was in center site. So the titaniumwas ease to form the vacancy in center site.The results of Dmol3 proved that the embedding energy for helium atom in vanadium was lower in tetrahedral interstitial she than in octahedron interstitial site which value was about 5eV. The embedding energy for helium atom in titanium was lower in octahedron interstitial site than in tetrahedral interstitial site which value was about 0.2eV.The values of three methods had some difference. There were two primary reasons. The first, the approximate grade for three methods were different. The EMT was not included of the exchange-interaction energy induced the value was on the large site. The CASTEP and Dmol3 were all electron calculation, so the value was accuracy. The second, the models of three methods were different. The EMT used super-cell. The CASTEP used periodic crystal structure. The Dmol3 used cluster. The tendency of results was consistent for three methods. So, the different methods of calculation could be selected in accordance to the different requirement.Compared with the diffusion behavior for helium atom in vanadium and titanium, helium atom was more stable in tetrahedral interstitial site of vanadium, and more stable in octahedron interstitial site of titanium. The embedding energy for helium in vanadium was higher than that in titanium, the diffusion barriers for helium a...