Andrej Antušek

Lone pair interactions with coinage metal atoms: Weak van der Waals complexes of the coinage metal atoms with water and ammonia

Interaction energies between the coinage metal atoms (Cu, Ag, and Au) and lone-pair donating molecules (H2O and NH3) are calculated by the spin adapted restricted open-shell Hartree–Fock coupled cluster method with the scalar relativistic effects accounted for by the Douglas–Kroll approximation. All ammonia complexes CuNH3, AgNH3, and AuNH3 are found to be of C3v symmetry with the counterpoise corrected interaction energies equal to −16.68, −6.87, and −14.64 mH for Cu, Ag, and Au, respectively. In the case of the water molecule the complexes are much weaker with the counterpoise corrected interaction energies equal to −3.78, −1.81, and −1.77 mH, for the three metal atoms, respectively. Moreover, all complexes with the water molecule are nonplanar. For both lone-pair donating molecules the structure and energetics of their complexes with the coinage metal atoms is mostly due to electron correlation effects. The relativistic effects are found to increase the bonding energies in the series of the ammonia com...

Ab initio study of interaction-induced NMR shielding constants in mixed rare gas dimers

The interaction-induced contribution to the NMR shielding constants in homonuclear A2 and heteronuclear AB (A,B=He,Ne,Ar) dimers is obtained ab initio by employing a coupled cluster singles and doubles with perturbative treatment of triples wave function model and extended correlation-consistent basis sets. The second virial coefficients entering the expansion of the property with the density are then computed in a fully quantum mechanical approach, for temperatures ranging from the limit of dissociation of the dimer to well above standard conditions. The results can be used to describe the density and temperature dependence of the shielding constants in binary mixtures of helium, neon, and argon. The predicted effects should be observable for the interaction of 21Ne with other rare gases.

Indirect NMR spin–spin coupling constants in diatomic alkali halides

We report the Nuclear Magnetic Resonance (NMR) spin-spin coupling constants for diatomic alkali halides MX, where M = Li, Na, K, Rb, or Cs and X = F, Cl, Br, or I. The coupling constants are determined by supplementing the non-relativistic coupled-cluster singles-and-doubles (CCSD) values with relativistic corrections evaluated at the four-component density-functional theory (DFT) level. These corrections are calculated as the differences between relativistic and non-relativistic values determined using the PBE0 functional with 50% exact-exchange admixture. The total coupling constants obtained in this approach are in much better agreement with experiment than the standard relativistic DFT values with 25% exact-exchange, and are also noticeably better than the relativistic PBE0 results obtained with 50% exact-exchange. Further improvement is achieved by adding rovibrational corrections, estimated using literature data.

Absolute shielding scales for Al, Ga, and In and revised nuclear magnetic dipole moments of 27Al, 69Ga, 71Ga, 113In, and 115In nuclei

We present coupled cluster calculations of NMR shielding constants of aluminum, gallium, and indium in water-ion clusters. In addition, relativistic and dynamical corrections and the influence of the second solvation shell are evaluated. The final NMR shielding constants define new absolute shielding scales, 600.0 ± 4.1 ppm, 2044.4 ± 31.4 ppm, and 4507.7 ± 63.7 ppm for aluminum, gallium, and indium, respectively. The nuclear magnetic dipole moments for (27)Al, (69)Ga, (71)Ga, (113)In, and (115)In isotopes are corrected by combining the computed shielding constants with experimental NMR frequencies. The absolute magnitude of the correction increases along the series and for indium isotopes it reaches approximately -8.0 × 10(-3) of the nuclear magneton.

Temperature dependence of the 1J(11B19F) spin–spin coupling in BF3 molecule

The 1J(11B19F) spin–spin coupling of gaseous BF3 was observed in 11B NMR spectra as a function of density in a wide range of temperatures. Following the extrapolation of the measured values to the zero‐density limit, the coupling constant free from intermolecular effects 1J0(11B19F) was obtained for each temperature. In contrast to previous investigations, the final results indicate a nonlinear dependence of 1J0(11B19F) on temperature. In the corresponding ab initio calculations of spin–spin coupling constants performed at the coupled cluster singles and doubles (CCSD) level to obtain a reliable result for this coupling constant we had to take into account large vibrational corrections. Copyright

Chapter 6:Accurate Non-relativistic Calculations of NMR Shielding Constants

We present a brief description of the non-relativistic methods of quantum chemistry used to determine NMR shielding constants, with the focus on the accuracy of the available results. Following an outline of the theory underlying the calculation of NMR parameters we proceed to the discussion of the most important computational aspects: the choice of the basis set and the treatment of the electron correlation effects. Modifications of the standard atomic basis sets, leading to faster convergence of computed shielding constants, are described. In the analysis of the correlation effects we concentrate on the hierarchy of ab initio methods, proceeding from the Hartree–Fock approximation to the coupled cluster perturbation theory approach. In addition, we comment on the importance of the relativistic and vibrational corrections and the basic approaches used to incorporate them. The magnitude of different contributions is considered and the accuracy of the total shielding constants is analyzed. The selected illustrative results were obtained primarily for small molecular systems, making the discussed theoretical values suitable for direct comparison with experimental data from gas phase NMR spectroscopy.

DFT Modeling of Cross-Linked Polyethylene: Role of Gold Atoms and Dispersion Interactions

Using DFT modeling, we analyze the concerted action of gold atoms and dispersion interactions in cross-linked polyethylene. Our model consists of two oligomer chains (PEn) with 7, 11, 15, 19, or 23 carbon atoms in each oligomer cross-linked with one to three Au atoms through C-Au-C bonds. In structures with a single gold atom the C-Au-C bond is located in the central position of the oligomer. Binding energies (BEs) with respect to two oligomer radical fragments and Au are as high as 362-489 kJ/mol depending on the length of the oligomer chain. When the dispersion contribution in PEn-Au-PEn oligomers is omitted, BE is almost independent of the number of carbon atoms, lying between 293 and 296 kJ/mol. The dispersion energy contributions to BEs in PEn-Au-PEn rise nearly linearly with the number of carbon atoms in the PEn chain. The carbon-carbon distance in the C-Au-C moiety is around 4.1 Å, similar to the bond distance between saturated closed shell chains in the polyethylene crystal. BEs of pure saturated closed shell PEn-PEn oligomers are 51-187 kJ/mol. Both Au atoms and dispersion interactions contribute considerably to the creation of nearly parallel chains of oligomers with reasonably high binding energies.