The Electronic States of Nickel ions in Diamond Calculated by a Discrete-Variational Xα Method

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The electronic states of nickel in diamond were calculated by a discrete-variational Xα (DV-Xα) method. Model clusters used for substitutional and interstitial Ni sites were [NiC_<28>H_<36>]^- (Ni^-_s center) and [NiC_<30>H_<40>]^+ (Ni^+_i center), respectively. Superhyperfine constants for electron paramagnetic resonance (EPR) spectra were estimated from results of DV-Xα calculation and were compared with measured values. A triply degenerate state with total spin S=3/2 appears in the Ni^-_s-center and a half-filled doubly degenerate state with total spin S=1/2 appears in the Ni^+_i-center. The total spin and electron occupancy of these clusters agree with the assignments of the EPR spectra. The electron population analysis result indicated that the N^+ ion at the tetrahedral interstitial site formed more ionic bonding than the Ni^- ion at the substitutional site. Superhyperfine interactions between Ni and the nearest-neighbor carbons were calculated as a function of Ni-C bond length, suggesting that a lattice relaxation occurred for the Ni-C bond to be elongated in the Ni^-_s center.
社団法人応用物理学会の論文
1997-03-15