Nuclear electric quadrupole moment of potassium from the molecular method

The current standard nuclear quadrupole moments (NQMs) of the ${}^{39}\mathrm{K}$, ${}^{40}\mathrm{K}$, and ${}^{41}\mathrm{K}$ isotopes have recently been contested by Singh and co-workers on the basis of their atomic computational data [Singh et al., Phys. Rev. A 86, 032509 (2012)]. Thus we performed relativistic calculations of electric field gradients at the potassium nuclei in three diatomic molecules (KF, KCl, and KBr) and combined these values with accurate experimental nuclear quadrupole coupling constants to provide an independent assessment of these NQMs. Our most accurate results, obtained by treating electron correlation with coupled cluster theory, employing a four-component Hamiltonian that includes the Gaunt two-electron correction, and with an incremented relativistic basis set of quadruple-ζ quality, yield $Q\left({}^{39}\mathrm{K}\right)=60.3\left(6\right)$, $Q\left({}^{40}\mathrm{K}\right)=–75.0\left(8\right)$, and $Q\left({}^{41}\mathrm{K}\right)=73.4\left(7\right)\mathrm{mb}$. These values are in better agreement with the results obtained by Singh et al. and indicate that the standard NQMs should be revised.