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Abstract: In this work, we investigate the influence of correlating core electrons on the relativistic corrections to the equilibrium geometries, harmonic frequencies and dissociation energies of hydrogen astatide, using moderately large basis sets. Our results suggest that relativistic effects tend to increase bond length and decrease harmonic frequencies and dissociation energies, in line with previous studies involving valence correlation. In all cases the driving force to the relativistic effects is the spin–orbit coupling, with scalar effects acting cooperatively except for the bond lengths. Core correlation counteracts the relativistic increase of bond lengths, but not strongly enough to reverse any trends. [Copyright &y& Elsevier]

Abstract: The electric nuclear quadrupole moment (NQM) of lutetium was determined by means of the molecular method. This method combines accurate calculations of electric field gradients (EFGs) at the nucleus with experimental values of nuclear quadrupole coupling constants (NQCCs). Relativistic Dirac–Coulomb coupled cluster calculations were performed to obtain the EFGs at lutetium in LuF and LuCl. These values were supplemented by a Gaunt interaction correction and a correction for the effect of truncating the active space on the electron correlation energy. Our results indicate that the NQMs of 175Lu and 176Lu are given by 3415(34) and 4818(48)mbarn, respectively. [Copyright &y& Elsevier]

Abstract: Commonly used exchange-correlations functionals are known to produce inaccurate electric field gradient (EFG) values at the nuclei of transition metals and heavy atoms in molecular calculations. This makes density functional theory (DFT) essentially inapplicable for the determination of nuclear quadrupole moments (NQM) from absolute EFG estimates. However, in a recently proposed indirect approach, the NQM is determined from the changes in the EFG along a series of molecules. We investigate this indirect approach within four-component relativistic DFT, showing that, at least in a series of chemically strictly related molecules, EFG variations can be computed quite accurately. This leads to surprisingly stable and reliable estimates of the NQM, even in notoriously ‘difficult’ cases such as 197Au. [Copyright &y& Elsevier]