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Abstract: The first implementation of analytical first-order one-electron molecular properties at the Dirac–Coulomb MP2 level of theory is described. The formalism presented allows for the use of inactive spinors. The method has been applied to the calculation of parity-violation energies in H2X2 (X=O, S, Se, and Te). Electron correlation does not play an important role for this property in this kind of systems, but the effect is shown to be very geometry dependent. [Copyright &y& Elsevier]

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]

Graphical abstract Abstract In the present article, we introduce the relativistic Cholesky-decomposed density (CDD) matrix second-order Møller-Plesset perturbation theory (MP2) energies. The working equations are formulated in terms of the usual intermediates of MP2 when employing the resolution-of-the-identity approximation (RI) for two-electron integrals. Those intermediates are obtained by substituting the occupied and virtual quaternion pseudo-density matrices of our previously proposed two-component (2C) atomic orbital-based MP2 (Helmich-Paris et al., 2016) by the corresponding pivoted quaternion Cholesky factors. While working within the Kramers-restricted formalism, we obtain a formal spin-orbit overhead of 16 and 28 for the Coulomb and exchange contribution to the 2C MP2 correlation energy, respectively, compared to a non-relativistic (NR) spin-free CDD-MP2 implementation. This compact quaternion formulation could also be easily explored in any other algorithm to compute the 2C MP2 energy. The quaternion Cholesky factors become sparse for large molecules and, with a block-wise screening, block sparse-matrix multiplication algorithm, we observed an effective quadratic scaling of the total wall time for heavy-element containing linear molecules with increasing system size. The total run time for both NR and 2C calculations was dominated by the contraction to the exchange energy. We have also investigated a bulky Te-containing supramolecular complex. For such bulky, three-dimensionally extended molecules the present screening scheme has a much larger prefactor and is less effective. [ABSTRACT FROM AUTHOR]

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]

The absolute configuration of a chiral molecule is key to its biological activity. Being able to find out what this configuration is, is thus crucial for a wide range of applications. The difficulties associated with such a determination steeply rise as the number of chiral centers in a given compound becomes larger. Concurrently, it becomes increasingly more challenging to determine the levels and identity of potential stereochemical contaminants in a given sample with one and the same technique, leading in practice to extensive and laborious efforts employing multiple analytical techniques. Here, experimental and theoretical studies based on Vibrational Circular Dichroism (VCD) are presented for dydrogesterone, a synthetic drug employed in reproductive medicine that is a prototypical example of such a multi-center chiral compound. We show that our approach allows us to distinguish and assign its absolute configuration without prior knowledge to one of the 64 possible stereoisomers associated with the six chiral centers. Studies on mixtures of dydrogesterone and 6-dehydroprogesterone, one of the diastereomers of dydrogesterone and generally the dominant impurity of dehydrogesterone, show that we can identify the presence of both compounds from one single VCD spectrum. Moreover, we find that we can determine diastereomeric contamination levels as low as 5% from the experimental VCD spectra. Image 1 • Stereochemistry of target and isomeric impurities determined with single technique. • Assignment absolute configuration of 6 stereocenters from one VCD spectrum. • Determination of stereomeric composition of mixtures. • Determination of diastereoisomeric impurity levels down to 5%. [ABSTRACT FROM AUTHOR]

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]