Molecular density functional calculations in the regular relativistic approximation: Method, application to coinage metal diatomics, hydrides, fluorides and chlorides, and comparison with first-order relativistic calculations Nonrelativistic and relativistic Hartree-Fock (HF) and configuration interaction (CI) calculations have been performed in order to analyze the relativistic and correlation effects in various diatomic gold compounds, It is found that relativistic effects reverse the trend in most molecular properties down the group (11). The consequences for gold chemistry are described. Relativistic bond stabilizations or destabilizations are dependent on the electronegativity of the ligand, showing the largest bond destabilization for AuF (86 kJlmol at the CI level) and the largest stabilization for AuLi ( -174 kJ Imol). Relativistic bond contractions lie between 1.09 (AuH+) and 0.16 A (AuF). Relativistic effects of various other properties are discussed. A number of as yet unmeasured spectroscopic properties, such as bondlengths ('e), dissociation energies (De)' force constants (k e ), and dipole moments (f1e), are predicted.

Small- and medium-core pseudopotentials representing [Ar]3d10- and [Kr]-like cores, respectively, have been adjusted for the In atom, supplementing the energy-consistent three-valence-electron large-core ([Kr]4d10 core) pseudopotential of the Stuttgart group. The performance of these potentials is tested against those of other groups and against experiment, in calculations for the ground-state potential curves of InH, InF, and InCl, both at the self-consistent-field and correlated levels. The role of the core size is discussed, and systematic errors of large- and medium-core pseudopotentials are analyzed.

A systematic search for global and energetically low-lying minimum structures of neutral gold clusters Au(n) (n=2-20) is performed within a seeded genetic algorithm technique using density functional theory together with a relativistic pseudopotential. Choosing the energetically lowest lying structures we obtain electronic properties by applying a larger basis set within an energy-consistent relativistic small-core pseudopotential approach. The possibility of extrapolating these properties to the bulk limit for such small cluster sizes is discussed. In contrast to previous calculations on cesium clusters [B. Assadollahzadeh et al., Phys. Rev. B 78, 245423 (2008)] we find a rather slow convergence of any of the properties toward the bulk limit. As a result, we cannot predict the onset of metallic character with increasing cluster size, and much larger clusters need to be considered to obtain any useful information about the bulk limit. Our calculated properties show a large odd-even cluster size oscillation in agreement, for example, with experimental ionization potentials and electron affinities. For the calculated polarizabilities we find a clear transition to lower values at Au14, the first cluster size where the predicted global minimum clearly shows a compact three-dimensional (3D) structure. Hence, the measurement of cluster polarizabilities is ideal to identify the 2D-->3D transition at low temperatures for gold. Our genetic algorithm confirms the pyramidal structure for Au20.

Two-component and scalar relativistic energy-consistent pseudopotentials for the group 1 elements from K to element 119 are presented using nine electrons for the valence space definition. The accuracy of such an approximation is discussed for dipole polarizabilities and ionization potentials obtained at the coupled-cluster level as compared to experimental and all-electron Douglas-Kroll results.

The cationic (C2H4)M+ complexes (M = Cu, Ag, and Au) have been examined by different ab initio molecular orbital, density functional (DFT), and density functional/Hartree−Fock (DFT/HF) hybrid methods using relativistic effective core potentials and a quasi-relativistic approach to account for relativistic effects. For (C2H4)Au+ a substantial relativistic stabilization is observed, such that the computed binding energies are almost twice as high than for (C2H4)Ag+ and still significantly higher than for (C2H4)Cu+. Structural features and energetics obtained at the various computational levels, although they differ significantly in their computational demands, are in satisfying agreement with each other, adding to the level of confidence that can be attributed to the computationally economic DFT and DFT/HF hybrid methods. In order to determine the nature of the bonding in these (C2H4)M+ complexes, an energy decomposition scheme is applied to the DFT results. For all three metal cations, the interaction with ethylene shows large covalent contributions. The major part of the covalent terms stems from σ-donor contribution from the ligand to the metal, whereas π-acceptor bonding (back-bonding) is less important. An atoms-in-molecules (AIM) analysis of the charge density distribution reveals cyclic structures for (C2H4)Au+ and (C2H4)Cu+, whereas (C2H4)Ag+ is T-shaped.

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The focus of this review is the presentation of the most important aspects of chemical bonding in molecules of the main group atoms according to the current state of knowledge. Special attention is given to the difference between the physical mechanism of covalent bond formation and its description with chemical bonding models, which are often confused. This is partly due to historical reasons, since until the development of quantum theory there was no physical basis for understanding the chemical bond. In the absence of such a basis, chemists developed heuristic models that proved extremely valuable for understanding and predicting experimental studies. The great success of these simple models and the associated rules led to the fact that the model conceptions were regarded as real images of physical reality. The complicated world of quantum theory, which eludes human imagination, made it difficult to link heuristic models of chemical bonding with quantum chemical knowledge. In the early days of quantum chemistry, some suggestions were made which have since proved untenable. In recent decades, there has been a stormy development of quantum chemical methods, which are not limited to the quantitative accuracy of the calculated properties. Also, methods have been developed where the experimentally developed models can be quantitatively expressed and visually represented using mathematically well-defined terms that are derived from quantum chemical calculations. The calculated numbers may however not be measurable values. Nevertheless, as orientation data for the interpretation and classification of experimental findings as well as a guideline for new experiments, they form a coordinate system that defines the multidimensional world of chemistry, which corresponds to the Hilbert space formalism of physics. The nonmeasurability of model values is not a weakness of chemistry but a characteristic by which the infinite complexity of the material world becomes scientifically accessible and very useful for chemical research. This review examines the basis of the commonly used quantum chemical methods for calculating molecules and for analyzing their electronic structure. The bonding situation in selected representative molecules of main-group atoms is discussed. The results are compared with textbook knowledge of common chemistry. CONTENTS1. Introduction 8782 2. The Physical Nature of the Chemical Bond 8783 3. Historical Development and Present Situation of Bonding Models for Main-Group Compounds: The Lewis Paradigm 8786 4. Quantum Chemical Methods for Calculating Molecular Structures and Properties 8787 4.1. Molecular Orbital (MO) Theory 8788 4.2. Density Functional Theory (DFT) 8789 4.3. Valence-Bond (VB) Theory 8790 5. Quantum Chemical Methods for Analyzing the Chemical Bond in Molecules 8790 5.1. Natural Bond Orbital Method (NBO) 8790 5.2. Quantum Theory of Atoms in Molecules (QTAIM) 8791 5.3. Energy Decomposition Analysis and Natural Orbitals for Chemical Valence (EDA-NOCV) 8792 6. Physical Reality and Chemical Bondi...

A 2018 update of the most accurate calculated and experimental static dipole polarizabilities of the neutral atoms in the Periodic Table from nuclear charge Z = 1 to 120 is given. Periodic trends are analyzed and discussed.