Two-dimensional angular correlation of positron annihilation radiation in vanadium

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Abstract
Two-photon momentum densities and the two-dimensional angular correlation of positron annihilation radiation (ACPAR) in V is calculated by using the band structure method due to Hubbard and Mihnarends (1972). The two-dimensional ACPAR curves N(pypz) calculated for four sets of momentum directions: (i) A: (pz, px)=((001),(100)); (ii) B: (pz,px)=((001), (110)); (iii) C: (pz,px)=((112), (111)); and (iv) D: (pz,px)=((110), (110)) all in the py=0 plane, are presented and the results are discussed in terms of the partial contributions from different bands and the Fermi surface topology. The results indicate which parts of the Fermi surface can be examined in each orientation (pz,px). In particular it is shown that the presence of the Fermi surface necks (along Gamma N) in V can alter the two-dimensional ACPAR curves significantly for the orientations B and D. The changes in the two-dimensional ACPAR curves in going from V to VD0.72 are calculated in the rigid band approximation and these results show interesting features. Long-slit ACPAR curves for V and VD0.72 are calculated.