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We report an implementation of the three-dimensional reference interaction site model (3D RISM) that in particular addresses the treatment of the long-range Coulomb field of charged species, represented by point charges and/or a distributed charge density. A comparison of 1D and 3D results for atomic ions demonstrates a reasonable accuracy, even for a moderate size of the unit cell and a moderate grid resolution. In an application to uranyl complexes with 4-6 explicit aqua ligands and an implicit bulk solvent modeled by RISM, we show that the 3D technique is not susceptible to the deficiencies of the 1D technique exposed in our previous work [Li, Matveev, Krüger, Rösch, Comp. Theor. Chem. 2015, 1051, 151]. The 3D method eliminates the artificial superposition of explicit aqua ligands and the RISM medium and predicts essentially the same values for uranyl and uranyl-water bond lengths as a state-of-the-art polarizable continuum model. With the first solvation shell treated explicitly, the observables are nearly independent of the order of the closure relationship used when solving the set of integral equations for the various distribution functions. Furthermore, we calculated the activation barrier of water exchange with a hybrid approach that combines the 3D RISM model for the bulk aqueous solvent and a quantum mechanical description (at the level of electronic density functional theory) of uranyl interacting with explicitly represented water molecules. The calculated result agrees very well with experiment and the best theoretical estimates.

To assess various ionic-core approximations we carried out density functional calculations on a series of octahedral palladium and gold model clusters M n with n = 13–147. We compared results for average bond lengths, cohesive energies, vertical ionization potentials, and electron affinities to the corresponding all-electron scalar relativistic results. We used extrapolated bulk values to compare with experiments. The results of the projector-augmented wave method agree best with the all-electron results. When modeling palladium–gold nanoalloy particles, one should keep in mind that current ECP or PAW modeling of palladium moieties appears to be more accurate than modeling of gold species.

Using the LCGTO-DFT + U methodology, we analyze the potential effect of self-interaction artifacts in standard Kohn-Sham (KS) density functional calculations on geometries, vibrational frequencies, and bonding for the example of the uranyl (VI) dication, both without and with explicit aqua ligands. We attribute the bent structure of the uranyl moiety in the penta-aqua complex to the limited accuracy of the Coulomb interaction of the U 5f orbitals afforded by common local or gradient-corrected exchange-correlation functionals. In particular, with scalar relativistic, all-electron Douglas-Kroll-Hess calculations we demonstrate that the distorted geometry of the uranyl penta-aqua complex is essentially rectified by the inclusion of a small positive on-site repulsion parameter. U(eff), for the 5f shell of the uranium atom. (C) 2010 Elsevier B.V. All rights reserved.

Using the DFT + U methodology with a localized basis set, we studied the role of Lu 4f orbitals in the bonding of LuF3. We carried out scalar relativistic all-electron Douglas-Kroll-Hess DFT calculations of geometry, atomization energy, and vertical ionization potentials without and with the Hubbard term. The on-site repulsion parameter U-eff for Lu 4f orbitals was estimated from reference atomic data. With U-eff > 0, atomic localization of the valence 4f-like molecular orbitals is recovered, thus removing the spurious mixing of Lu 4f and F 2p orbitals present in standard Kohn-Sham calculations, while the molecular properties of LuF3 remained unchanged. (C) 2008 Elsevier B. V. All rights reserved.

We present a general strategy for interpreting optical spectra of interacting systems on the basis of linear-response time-dependent density functional theory (TDDFT) calculations. For this purpose, we combined a natural transition orbitals (NTO) analysis with a fragment molecular orbital (FMO) analysis. The NTO transformation allows one to identify leading contributions of particle-hole excitations in the spectral bands, whereas the FMO analysis characterizes each pair in terms of (leading) contributions of the corresponding fragments. We applied this procedure to assign and characterize optical transitions of coinage metal dimers M2 (M = Cu, Ag, Au) adsorbed at regular oxygen sites of MgO(001) as well as at oxygen vacancies, Fs and F. The TDDFT calculations were carried out at the generalized-gradient level on structures that had been obtained with cluster models embedded in an elastic polarizable environment. The combined NTO and FMO results allowed us to analyze the spectra both qualitatively and quantitatively. The qualitative results agree very well with a previous assignment carried out by our group (Bosko et al., J Phys Chem A, 2007, 111, 6870), whereas the present approach yields a straightforward and transparent quantitative characterization of the main spectral bands. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Polarization-resolved optical spectra of coinage metal monomers and dimers Mn (M = Cu, Ag, Au; n = 1, 2) at ideal O2- sites of MgO(001) as well as at oxygen vacancies, Fs and Fs+, of that surface were established using a computational approach based on linear response time-dependent density functional theory. Calculations were performed for structures determined by applying a generalized-gradient density functional method to cluster models embedded in an elastic polarizable environment. This embedding scheme provides an accurate description of substrate relaxation and long-range electrostatic interaction. We compared the optical properties of adsorbed atoms and dimers with those of the corresponding gas-phase species and we systematically analyzed trends among congeners.

We investigated Boettger’s screened nuclear potential approximation for the spin–orbit interaction (SNSO) in the context of the Douglas–Kroll approach to relativistic Kohn–Sham theory. We extended the approximation to second-order terms and evaluated it for various atomic and molecular properties (spin–orbit splittings, g -tensor shifts, bond lengths, vibrational frequencies and binding energies) and compared the SNSO results with those of a self-consistent relativistic treatment of the electron–electron (ee) interaction. The SNSO approximation is comparable in computational effort to the model based on the nuclear potential only, but delivers molecular results that agree well with those of the more exact ee treatment.

A two-component relativistic density functional method based on the Douglas-Kroll-Hess transformation has been applied to the actinyls and hexafluorides of U and Np. All-electron scalar relativistic calculations as well as calculations including spin-orbit interaction have been compared to results obtained with a pseudopotential approach. In addition, several exchange-correlation potentials have been applied to examine their performance for the bond lengths and vibrational frequencies of the title compounds. The calculations confirm the well-known accuracy of the LDA approach for geometries and frequencies, which is corroborated for the hexafluorides where gas phase experimental data are available. Comparison with results of accurate wave function based methods provides further confirmation of this finding. Gradient-corrected functionals tend to overestimate bond lengths and underestimate frequencies also for actinide compounds. The results obtained with Stoll-Preuss (small core) effective core potentials agree very well with those of all-electron calculations, while calculations with Hay-Martin large core pseudopotentials are somewhat less accurate. For all molecules and properties considered, spin-orbit effects have been found negligible concomitant with the closed-shell electronic structure of the U(VI) compounds and the open-shell situation of the Np(VI) compounds with a single valence f electron.