Ab-initio calculations of electric field gradient in Ru compounds and their implication on the nuclear quadrupole moments of ⁹⁹Ru and ¹⁰¹Ru

The nuclear quadrupole moments, Q, for the ground and first excited states in ⁹⁹Ru and ground state of ¹⁰¹Ru have been determined by comparing the experimentally observed quadrupole interaction frequencies ν with calculated electric field gradient (EFG) for a large number of Ru-based compounds. The calculations of EFG were performed using the all-electron augmented plane wave + local orbital (APW + 1o) method of the density functional theory (DFT). From the slope of the linear correlation between theoretically calculated EFGs and experimentally observed ν_Q, we obtain the quadrupole moment for the (5/2⁺) ground state in ⁹⁹Ru and ¹⁰¹Ru as 0.0734(17)b and 0.431(14)b respectively, showing excellent agreement with the values reported in literature. For 3/2⁺, the quadrupole moment of the first excited state in ⁹⁹Ru is obtained as +0.203(3) b, which is considerably lower than the commonly accepted literature value of +0.231(12) b. The results presented in this paper would be useful for the precise determination of quadrupole moment of high spin states in other Ru isotopes and is likely to stimulate further shell model calculations for an improved understanding of nuclear shape in these nuclei. (author)