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The current standard nuclear quadrupole moments (NQMs) of the 39K, 40K, and 41K isotopes have recently been contested by Singh and co-workers on the basis of their atomic computational data [Singh et ai, 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(39K) = 60.3(6), Q(40K) = -75.0(8), and Q(41K) = 73.4(7)mb. These values are in better agreement with the results obtained by Singh el al. and indicate that the standard NQMs should be revised. [ABSTRACT FROM AUTHOR]

The past few years have witnessed a remarkable interest in the application of quantum computing for solving problems in quantum chemistry more efficiently than classical computers allow. Very recently, proof-of-principle experimental realizations have been reported. However, so far only the nonrelativistic regime (i.e., the Schrödinger equation) has been explored, while it is well known that relativistic effects can be very important in chemistry. We present a quantum algorithm for relativistic computations of molecular energies. We show how to efficiently solve the eigenproblem of the Dirac-Coulomb Hamiltonian on a quantum computer and demonstrate the functionality of the proposed procedure by numerical simulations of computations of the spin-orbit splitting in the SbH molecule. Finally, we propose quantum circuits with three qubits and nine or ten controlled-NOT (CNOT) gates, which implement a proof-of-principle relativistic quantum chemical calculation for this molecule and might be suitable for an experimental realization. [ABSTRACT FROM AUTHOR]

We report the implementation of a general-order relativistic coupled-cluster method for performing high- precision calculations of atomic and molecular properties. As a first application, the black-body radiation shift of the AP clock has been estimated precisely. The computed shift relative to the frequency of the 3s² 1Se0 → 3s3p ³Po0 clock transition given by (-3.66 ± 0.60) x 10-18 calls for an improvement over the recent measurement with a reported result of (-9 ± 3) × l0-18 [Phys. Rev. Lett. 104, 07O802 (2010)]. [ABSTRACT FROM AUTHOR]