Density functional theory study of indirect nuclear spin-spin coupling constants with spin-orbit corrections

Theoretical and experimental study on the electronic and optical properties of K0.5Rb0.5Pb2Br5: a promising laser host material

The data on the electronic structure and optical properties of bromide K_0.5Rb_0.5Pb₂Br₅ achieved by first-principle calculations and verified by X-ray spectroscopy measurements are reported. The kinetic energy, the Coulomb potential induced by the exchange hole, spin-orbital effects, and Coulomb repulsion were taken into account by applying the Tran and Blaha modified Becke–Johnson function (TB-mBJ), Hubbard U parameter, and spin-orbital coupling effect (SOC) in the TB-mBJ + U + SOC technique. The band gap was for the first time defined to be 3.23 eV. The partial density of state (PDOS) curves of K_0.5Rb_0.5Pb₂Br₅ agree well with XES K Ll and Br Kβ₂, and XPS spectra. The valence band (VB) is characterized by the Pb-5d_3/2 and Pb-5d_5/2 sub-states locating in the vicinities of −20 eV and −18 eV, respectively. The VB middle part is mainly formed by K-3p, Rb-4p and Br-4s states, in which the separation of Rb-4p_3/2 and Rb-4p_1/2 was also observed. The strong hybridization of Br-p and Pb-s/p states near −6.5 eV reveals a major covalent part in the Br–Pb bonding. With a large band gap of 3.23 eV, and the remarkably high possibility of inter-band transition in energy ranges of 4–7 eV, and 10–12 eV, the bromide K_0.5Rb_0.5Pb₂Br₅ is expected to be a very promising active host material for core valence luminescence and mid-infrared rare-earth doped laser materials. The anisotropy of optical properties in K_0.5Rb_0.5Pb₂Br₅ is not significant, and it occurs at the extrema in the optical spectra. The absorption coefficient α(ω) is in the order of magnitude of 10⁶ cm⁻¹ for an energy range of 5–25 eV.

The data on the electronic structure and optical properties of bromide K_0.5Rb_0.5Pb₂Br₅ achieved by first-principle calculations and verified by X-ray spectroscopy measurements are reported.

Relativistic effects in the one-bond spin-spin coupling constants involving selenium

One-bond spin-spin coupling constants involving selenium of seven different types, (1)  J(Se,X), X = (1) H, (13) C, (15)  N, (19)  F, (29) Si, (31) P, and (77) Se, were calculated in the series of 14 representative compounds at the SOPPA(CCSD) level taking into account relativistic corrections evaluated both at the RPA and DFT levels of theory in comparison with experiment. Relativistic corrections were found to play a major role in the calculation of (1)  J(Se,X) reaching as much as almost 170% of the total value of (1)  J(Se,Se) and up to 60-70% for the rest of (1)  J(Se,X). Scalar relativistic effects (Darwin and mass-velocity corrections) by far dominate over spin-orbit coupling in the total relativistic effects for all (1)  J(Se,X). Taking into account relativistic corrections at both random phase approximation and density functional theory levels essentially improves the agreement of theoretical results with experiment. The most 'relativistic' (1)  J(Se,Se) demonstrates a marked Karplus-type dihedral angle dependence with respect to the mutual orientation of the selenium lone pairs providing a powerful tool for stereochemical analysis of selenoorganic compounds.

[Pt@Pb12]2– — A challenging system for relativistic density functional theory calculations of 195Pt and 207Pb NMR parameters

We report computations of NMR chemical shifts and indirect spin-spin coupling constants (J couplings) for the [Pt@Pb12]2– “superatom”. The system is strongly influenced by relativistic effects. The Pt–Pb coupling constant is predicted to be negative, with its magnitude being in reasonable agreement with experiment. Pt and Pb chemical shifts also agree reasonably well with experiment. The Pb shielding tensor is strongly anisotropic, with a large deshielding principal component dominated by magnetic coupling between frontier orbitals of the cluster that resemble atomic g orbitals. The NMR parameters are sensitive to approximations made in the computations and require the inclusion of spin-orbit coupling in the theoretical model to achieve reliable results. Computing the NMR parameters of the compact [Pt@Pb12]2– system with its many electrons proves to be a challenging test case for relativistic density functional methods.