• N C Mohapatra

      Articles written in Pramana – Journal of Physics

    • Bloch enhancement of electric field gradient in Fe and Cu host alloys

      P Tripathi N C Mohapatra

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      The Bloch enhancement factor α(kf) of the electric field gradient has been evaluated for the half-filledd-core Fe host metal and completely filledd-core Cu host metal in single orthogonalized plane wave (OPW) approximation. For this purpose the radially-dependent antishielding factors,γ(r) have been calculated in non-orthogonal Hartree-Fock perturbation theory (NHFPT). The results show that the contributions of antishielding to α(kf) from the plane wave-plane wave part and the core part of the OPW state are individually large but opposite in sign and thereby lead to partial cancellation. The net effect of antishielding on α(kf) is found to be − 5.6% in Fe and 14% in Cu.

    • Electric field gradient in transition metal — scandium

      B B Panigrahi N C Mohapatra

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      Electric field gradient inhcp transition metal scandium has been calculated as the sum of contributions from lattice ions and conduction electrons. For the lattice contributionqlatt, a point-charge model has been assumed. The contribution from conduction electronsqel, on the other hand, has been evaluated by carrying out an energy-band calculation using non-local transition-metal model potential. The results obtained are:qel=−106.11×1013 esu/cm3 andqlatt=122.17×1013 esu/cm3. The net field gradient (qel+qlatt) of 16.06×1013 esu/cm3 agrees quite well with the experimental result, |qexpt|=13×1013 esu/cm3. Directions of further improvement in the theory are discussed.

    • Electronic contribution to electric field gradient in β-gallium

      B K Acharya N C Mohapatra

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      Electronic contribution to electric field gradient (EFG) inβ-Ga has been calculated for the first time using the band wave functions. The results show that the magnitudes of the quadrupole resonance frequency and the net EFG agree with experiment to within 7% and 2% respectively.

    • Electric field gradient in transition metal: Scandium

      B B Panigrahi N C Mohapatra

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      Corrections to results of electric field gradient (EFG) already published [Pramana — J. Phys.41, 443 (1993)] are reported. The corrected net EFG is:q=−8.01×1013 esu/cm3 against the published valueq=16.06×1013 esu/cm3. The present result agrees reasonably well with the experimental result, |qexpt|=13×1013 esu/cm3.

      Recently, a computational error is detected, which modifies the results of EFG, we have already published [1]. The error was committed mainly in the part that evaluated thep-p contribution [1] to EFG by the conduction electrons. The corrected results are summarized in table 1 which must replace the table 1 of the published work [1].

      In addition, the lattice parameters as well as the temperature were also misquoted in the previous work [1]. The right parameters are:a=6.25311 au andc=9.96509 au. The temperature at which EFG’s are calculated is 293 K instead of 11 K as reported before [1].

      The discussions and conclusions made in the published work [1] remain almost unchanged except that they now refer to the corrected numbers. Although the corrected net EFG suffers a sign reversal from the one already published [1], the agreement with experiment is still considered reasonably good because the sign of experimental EFG is not determined. The computational error however does not affect the introduction and theory section of the published work [1].

    • Temperature variation of electric field gradient in scandium metal

      B B Panigrahi N C Mohapatra

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      Electric field gradient (EFG) in scandium metal has been evaluated at temperatures 11 K and 293 K using band wave functions determined in the temperature dependent model potentials. The results of net EFG obtained are −3.756×1013 esu/cm3 and −8.009×1013esu/cm3 at 11 K and 293 K respectively. The agreement with available experimental result is reasonably good.

    • Compton profiles of electron momentum distribution inβ-Ga

      B K Acharya N C Mohapatra

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      We report for the first time the Compton profiles of electron momentum distribution inβ-gallium calculated along the crystallographic directions (100), (110) and (111). The conduction electron states for this purpose are determined in the energy band calculations using model potential. The core states, on the other hand, are represented each by a single tight-binding function. The results show that the Compton profiles are nearly isotropic with very little directional dependence, which is suggestive of a free-electron-like distribution of the conduction electrons in this system. The latter conclusion is in close confirmity with similar conclusions drawn in augmented plane wave (APW) calculation of energy bands and the derived Knight-shift results inβ-Ga.

    • Radially dependent antishielding factor γ(r) of the Sc3+ ion in the solid state

      B B Panigrahi N C Mohapatra S Hafizuddin

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      We report the results of our calculation of γ(r), the radially dependent antishielding factor of Sc3+ ion in the crytalline environment. Watson sphere model is used to approximately represent the crystal potential. Differential equations resulting from non-orthogonal Hartree-Fock perturbation theory are solved to obtain perturbations to core electron states. Contribution to γ(r) from electron self-consistency effect has been evaluated by using the latter wave-functions in the many-body expression of Schmidtet al.

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