Showing papers on "Electronic structure published in 2003"
TL;DR: MOLCAS as discussed by the authors is a package for calculations of electronic and structural properties of molecular systems in gas, liquid, or solid phase, which contains a number of modern quantum chemical methods for studies of the electronic structure in ground and excited electronic states.
1,678 citations
TL;DR: Diazonium reagents functionalize single-walled carbon nanotubes suspended in aqueous solution with high selectivity and enable manipulation according to electronic structure to reverse the chemistry by using a thermal treatment that restores the pristine electronic structure of the nanotube.
Abstract: Diazonium reagents functionalize single-walled carbon nanotubes suspended in aqueous solution with high selectivity and enable manipulation according to electronic structure. For example, metallic species are shown to react to the near exclusion of semiconducting nanotubes under controlled conditions. Selectivity is dictated by the availability of electrons near the Fermi level to stabilize a charge-transfer transition state preceding bond formation. The chemistry can be reversed by using a thermal treatment that restores the pristine electronic structure of the nanotube.
1,332 citations
TL;DR: The linearized-augmented-plane-wave method is one of the most accurate methods for solving the density functional theory (DFT) problem as discussed by the authors. But it is computationally expensive.
971 citations
TL;DR: This review discusses methods for the incorporation of quantum mechanical effects into enzyme kinetics simulations in which the enzyme is an explicit part of the model.
Abstract: ▪ Abstract This review discusses methods for the incorporation of quantum mechanical effects into enzyme kinetics simulations in which the enzyme is an explicit part of the model. We emphasize three aspects: (a) use of quantum mechanical electronic structure methods such as molecular orbital theory and density functional theory, usually in conjunction with molecular mechanics; (b) treating vibrational motions quantum mechanically, either in an instantaneous harmonic approximation, or by path integrals, or by a three-dimensional wave function coupled to classical nuclear motion; (c) incorporation of multidimensional tunneling approximations into reaction rate calculations.
699 citations
TL;DR: In this article, the first energy transition 1h − 1e as a function of x and the well width was calculated for cubic AlxGa1−xN/GaN/AlxGa 1 −xN quantum wells and the nearest neighbor sp 3 s ∗ empirical tight binding approximation, together with the Surface Green Function Matching method was used.
Abstract: For cubic AlxGa1−xN/GaN/AlxGa1−xN quantum wells we calculated the first energy transition 1h–1e as a function of x and the well width. The nearest neighbour sp 3 s ∗ empirical tight binding approximation, including spin-orbit interaction, together with the Surface Green Function Matching method is used.
543 citations
TL;DR: TPR measurements of CO oxidation have shown that the smallest gold cluster that catalyzes the reaction is Au8, and while Au4 is catalytically inert, the doped cluster Au3Sr is active, and findings are revealed that underlying the aforementioned remarkable chemical size-sensitivity is the nature of bonding and the activation of molecular oxygen by these nanocluster catalysts.
Abstract: Metal clusters exhibit unique size-dependent physical[1] and chemical properties[2] that differ from those of bulk materials. While inert as a bulk material, gold nanoparticles and clusters have attracted considerable interest lately as active catalysts for a number of industrially relevant reactions.[3–6] Unlike supported particles of larger size or extended solid surfaces,[7–10] size-selected small metal clusters adsorbed at specific sites of a support material (e.g. oxygen vacancies in the case of a MgO(100) surface) exhibit unique properties that originate from the highly reduced dimensions of the individual metal aggregates. These properties underlie the remarkable, newly found catalytic activity of small gold clusters, and they include: 1) dynamic structural fluxionality that exhibits itself through the propensity of small clusters to transform, in the course of chemical reactions, between various energetically accessible structural isomers, thus enhancing the rates for overcoming reaction barriers, 2) quantum size effects that are reflected in size-dependent characteristics of the electronic spectra of small gold clusters, and in charge transfer from the support to the clusters, 3) impurity-doping effects that allow modification and control of the electronic structure, and consequently the chemical reactivity, of small supported clusters, through incorporation of judiciously chosen impurity atoms in otherwise inert clusters. Herein, we focus on gaining fundamental insights into the above size-dependent “nanocatalytic factors”, and illustrate through experimental and theoretical investigations the manner in which such fundamental understanding may guide the design and atomic-scale modifications of nanocatalysts. Recently, a set of model catalysts have been prepared by soft-landing[11] of mass-selected Aun and AunSr cluster ions onto well-characterized MgO(100) thin films. These substrate films contained a low concentration (typically 5 6 1013 cm 1) of oxygen vacancies (surface F-centers, FC), that act as strong trapping sites for the clusters at low temperatures.[12–14] Temperature-programmed reaction (TPR) measurements of CO oxidation (CO+ =2O2!CO2) have shown that the smallest gold cluster that catalyzes the reaction is Au8. Furthermore, it has been found that while Au4 is catalytically inert, the doped cluster Au3Sr is active. These findings, in conjunction with ab initio calculations, have revealed that underlying the aforementioned remarkable chemical size-sensitivity is the nature of bonding and the activation of molecular oxygen by these nanocluster catalysts. The measured chemical activity is summarized in Figure 1, which shows typical TPR spectra for selected samples (a–e). The total CO2 yield per cluster obtained in a one-cycle heating experiment for Aun and AunSr with 1 n 9 is shown in the inset. The active model systems (n 8 for the pure Aun and
521 citations
TL;DR: F Fourier transform studies of atomic-scale spatial modulations in the Bi-2212 density of states show strong similarities to the structure of the occupied states, and the copper oxide quasiparticles apparently exhibit particle–hole mixing similar to that of conventional superconductors.
Abstract: The electronic structure of simple crystalline solids can be completely described in terms either of local quantum states in real space (r-space), or of wave-like states defined in momentum-space (k-space). However, in the copper oxide superconductors, neither of these descriptions alone may be sufficient. Indeed, comparisons between r-space and k-space studies of Bi2Sr2CaCu2O8+delta (Bi-2212) reveal numerous unexplained phenomena and apparent contradictions. Here, to explore these issues, we report Fourier transform studies of atomic-scale spatial modulations in the Bi-2212 density of states. When analysed as arising from quasiparticle interference, the modulations yield elements of the Fermi-surface and energy gap in agreement with photoemission experiments. The consistency of numerous sets of dispersing modulations with the quasiparticle interference model shows that no additional order parameter is required. We also explore the momentum-space structure of the unoccupied states that are inaccessible to photoemission, and find strong similarities to the structure of the occupied states. The copper oxide quasiparticles therefore apparently exhibit particle-hole mixing similar to that of conventional superconductors. Near the energy gap maximum, the modulations become intense, commensurate with the crystal, and bounded by nanometre-scale domains. Scattering of the antinodal quasiparticles is therefore strongly influenced by nanometre-scale disorder.
406 citations
TL;DR: In this article, angle-integrated photoemission measurements of carbon nanotubes (SWNTs) are reported, revealing an oscillation in the pi-electron density of states owing to one-dimensional van Hove singularities.
Abstract: The electronic transport properties of conventional three-dimensional metals are successfully described by Fermi-liquid theory. But when the dimensionality of such a system is reduced to one, the Fermi-liquid state becomes unstable to Coulomb interactions, and the conduction electrons should instead behave according to Tomonaga-Luttinger-liquid (TLL) theory. Such a state reveals itself through interaction-dependent anomalous exponents in the correlation functions, density of states and momentum distribution of the electrons. Metallic single-walled carbon nanotubes (SWNTs) are considered to be ideal one-dimensional systems for realizing TLL states. Indeed, the results of transport measurements on metal-SWNT and SWNT-SWNT junctions have been attributed to the effects of tunnelling into or between TLLs, although there remains some ambiguity in these interpretations. Direct observations of the electronic states in SWNTs are therefore needed to resolve these uncertainties. Here we report angle-integrated photoemission measurements of SWNTs. Our results reveal an oscillation in the pi-electron density of states owing to one-dimensional van Hove singularities, confirming the one-dimensional nature of the valence band. The spectral function and intensities at the Fermi level both exhibit power-law behaviour (with almost identical exponents) in good agreement with theoretical predictions for the TLL state in SWNTs.
396 citations
01 Jan 2003-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, the electronic structure of ZnO and its defects, which include intrinsic point defects and their complexes, have been calculated using full-potential linear Muffin-tin orbital method.
Abstract: The electronic structure of ZnO and its defects, which include intrinsic point defects and their complexes, have been calculated using full-potential linear Muffin-tin orbital method. According to our calculation data, the positions of the defect state levels have been determined in the energy band of ZnO. Based on the results above, we analysis the mechanism of the absorption and emission spectra of ZnO and discuss the effects of the electronic structure of complete ZnO and its defects on the spectral properties.
392 citations
TL;DR: In this paper, the electronic energy band structure, density of states (DOS) and charge density contour of KNbO3 in the paraelectric cubic phase have been studied using the full-potential linearized augmented plane wave method within the generalized gradient approximation for exchange and correlation.
Abstract: The electronic energy band structure, density of states (DOS) and charge density contour of KNbO3 in the paraelectric cubic phase have been studied using the full-potential linearized augmented plane wave method within the generalized gradient approximation for exchange and correlation. The band structure shows an indirect (R–Γ) band gap. From the DOS analysis as well as charge density studies, we find that the bonding between K and NbO3 is mainly ionic while that between Nb and O is covalent. We have also reported results on the pressure variation of the energy gap of this compound and found that the band gap increases with increasing pressure. In order to understand the optical properties of the perovskite, the real and imaginary parts of the dielectric function, reflectivity, absorption coefficient, optical conductivity, electron energy-loss function, refractive index and extinction coefficient were calculated. The general profiles of the optical spectra were analysed and origins of the structures discussed.
370 citations
TL;DR: In this article, DFT simulations are combined with quantum dynamics calculations of electronic relaxation to investigate the interfacial electron transfer in catechol/TiO2-anatase nanostructures under vacuum conditions.
Abstract: Ab initio DFT molecular dynamics simulations are combined with quantum dynamics calculations of electronic relaxation to investigate the interfacial electron transfer in catechol/TiO2-anatase nanostructures under vacuum conditions. It is found that the primary process in the interfacial electron-transfer dynamics involves an ultrafast (τ1 ≃ 6 fs) electron-injection event that localizes the charge in the Ti4+ surface ions next to the catechol adsorbate. The primary event is followed by charge delocalization (i.e., carrier diffusion) through the TiO2-anatase crystal, an anisotropic diffusional process that can be up to an order of magnitude slower along the [−101] direction than carrier relaxation along the [010] and [101] directions in the anatase crystal. It is shown that both the mechanism of electron injection and the time scales for interfacial electron transfer are quite sensitive to the symmetry of the electronic state initially populated in the adsorbate molecule. The results are particularly releva...
TL;DR: In this paper, a detailed theoretical study of nanoparticles was performed using density functional theory (DFT) and the edge structures of the edges of the nanoparticles were investigated, and a model for calculating Gibbs free energy of the edge in terms of the DFT energies was presented.
Abstract: Using density-functional theory (DFT) we present a detailed theoretical study of ${\mathrm{MoS}}_{2}$ nanoparticles. We focus on the edge structures, and a number of different edge terminations are investigated. Several, but not all, of these configurations have one-dimensional metallic states localized at the edges. The electronic structure of the edge states is studied and we discuss their influence on the chemical properties of the edges. In particular, we study the reactivity towards hydrogen and show that hydrogen may form stable chemical bonds with both the two low-Miller indexed edges of ${\mathrm{MoS}}_{2}.$ A model for calculating Gibbs free energy of the edges in terms of the DFT energies is also presented. This model allows us to determine the stable edge structure in thermodynamic equilibrium under different conditions. We find that both the insulating and metallic edges may be stable depending on the temperature and the composition of the gas phase. Using the Tersoff-Hamann formalism, scanning-tunneling microscopy (STM) images of the edges are simulated for direct comparison with recent STM experiments. In this way we identify the experimentally observed edge structure.
TL;DR: In this paper, the relationship between composition, crystal structure and the electronic structure of oxides containing octahedrally coordinated d0 transition metal ions was quantitatively investigated using linear muffin tin orbital methods and UV-visible diffuse reflectance spectroscopy, respectively.
TL;DR: The present approach provides structural images and electronic characterization of the metal-molecule-metal junction, thereby elucidating the nature of the contacts between the molecule and metal in this junction.
Abstract: Artificial nanostructures, each composed of a copper(II) phthalocyanine (CuPc) molecule bonded to two gold atomic chains with a controlled gap, were assembled on a NiAl(110) surface by manipulation of individual gold atoms and CuPc molecules with a scanning tunneling microscope. The electronic densities of states of these hybrid structures were measured by spatially resolved electronic spectroscopy and systematically tuned by varying the number of gold atoms in the chains one by one. The present approach provides structural images and electronic characterization of the metal-molecule-metal junction, thereby elucidating the nature of the contacts between the molecule and metal in this junction.
TL;DR: In this paper, the DFT + U method was used to predict the structural and electronic properties of transition-metal sulfides formed by 3D transition metal atoms, including magneto-volume effects and magneto structural effects.
Abstract: Density-functional studies of structural and electronic properties of transition-metal sulfides formed by 3d transition metals, based on the local spin-density approximation and including non-local corrections to the exchange–correlation functional (generalized gradient approximation), have demonstrated the importance of magneto-volume effects and magneto-structural effects, but could not achieve full agreement with experiment. A further improvement is to consider electronic correlation effects due to tightly bound and localized d-states on the transition metal atoms. With the DFT + U method used in this work, these correlation effects are taken in account and yield improved predictions for volume, magnetic moment, exchange splitting and bandgap. For MnS the semiconducting gap is correctly predicted, and for MnS2 the high-spin AFM type-III state can be stabilized over the low-spin state. For FeS even weak correlation effects lead to better predictions for the semiconducting gap, volume and magnetic moment.
TL;DR: A combined Density Functional/Time Dependent Density functional study of the molecular structure, electronic states, and optical absorption spectrum of [Ru(4,4'-COOH-2,2'-bpy)(2)(NCS)(2)], a widely used charge-transfer sensitizer in nanocrystalline TiO(2) solar cells.
Abstract: We present a combined Density Functional/Time Dependent Density Functional study of the molecular structure, electronic states, and optical absorption spectrum of [Ru(4,4‘-COOH-2,2‘-bpy)2(NCS)2], a widely used charge-transfer sensitizer in nanocrystalline TiO2 solar cells. Calculations have been performed both for the complex in vacuo and in ethanol and water solvents, using a continuum model to account for solute−solvent interactions. Inclusion of the solvent leads to important changes of the energies and composition of the molecular orbitals of the complex; as a consequence, whereas the computed spectrum for the Ru-complex in vacuo deviates from the experimental one in both energy and shape, the spectra calculated in the presence of the solvent are in good agreement with the experiment. The first two absorption bands are found to originate from mixed ruthenium-NCS to bipyridine-π* transitions rather than to pure metal-to-ligand-charge-transfer (MLCT) transitions, whereas the third band arises from intra...
TL;DR: In this paper, a linearized-augmented-plane-wave (LAPW) method is used to solve the Kohn-Sham (KS) equations, which is used in the computer code WIEN2k to study crystal properties on the atomic scale.
TL;DR: A dynamical mean-field approach for calculating the electronic structure of strongly correlated materials from first principles, which avoids the conceptual problems inherent to conventional "LDA+DMFT," such as Hubbard interaction parameters and double-counting terms.
Abstract: We propose a dynamical mean-field approach for calculating the electronic structure of strongly correlated materials from first principles. The scheme combines the $GW$ method with dynamical mean-field theory, which enables one to treat strong interaction effects. It avoids the conceptual problems inherent to conventional ``$\mathrm{L}\mathrm{D}\mathrm{A}+\mathrm{D}\mathrm{M}\mathrm{F}\mathrm{T}$,'' such as Hubbard interaction parameters and double-counting terms. We apply a simplified version of the approach to the electronic structure of nickel and find encouraging results.
TL;DR: In this paper, correlation consistent basis sets augmented by multiple diffuse functions were used to obtain the first high-quality theoretical results for substituent effects in π-stacking interactions, which should be accurate within several tenths of a kcal mol-1 all substituted dimers bind more strongly than benzene dimer, with benzene−benzonitrile binding the most strongly
Abstract: State-of-the-art electronic structure methods have been applied to obtain the first high-quality theoretical results for substituent effects in π-stacking interactions The sandwich configurations of benzene dimer, benzene−phenol, benzene−toluene, benzene−fluorobenzene, and benzene−benzonitrile have been studied using correlation consistent basis sets augmented by multiple diffuse functions, namely aug-cc-pVDZ and aug-cc-pVTZ, at the second-order perturbation theory (MP2) level Coupled-cluster computations with perturbative triples [CCSD(T)] were performed and combined with the above MP2 calculations to estimate the CCSD(T)/aug-cc-pVTZ binding energies, which should be accurate within several tenths of a kcal mol-1 All substituted dimers bind more strongly than benzene dimer, with benzene−benzonitrile binding the most strongly Both electrostatic and dispersion interactions contribute to the increased binding of the monosubstituted dimers
TL;DR: Spectroscopically determined wire band gaps compare closely to those calculated by the semiemipirical pseudopotential method, confirming 2D quantum confinement and suggesting that a length of ca.
Abstract: Soluble CdSe quantum wires are prepared by the solution-liquid-solid mechanism, using monodisperse bismith nanoparticles to catalyze wire growth. The quantum wires have micrometer lengths, diameters in the range of 5-20 nm, and diameter distributions of +/-10-20%. Spectroscopically determined wire band gaps compare closely to those calculated by the semiemipirical pseudopotential method, confirming 2D quantum confinement. The diameter dependence of the quantum wire band gaps is compared to that of CdSe quantum dots and rods. Quantum rod band gaps are shown to be delimited by the band gaps of dots and wires of like diameter, for short and long rods, respectively. The experimental data suggest that a length of ca. 30 nm is required for the third dimension of quantum confinement to fully vanish in CdSe rods. That length is about six times the bulk CdSe exciton Bohr radius.
TL;DR: This review is summarise the quantum chemistry studies carried out by several groups over the last ten years on polyoxometalates, or polyoxoanions, an immense family of compounds made up of transition metal ions in their highest oxidation state and oxo ligands.
Abstract: In this review we summarise the quantum chemistry studies carried out by several groups over the last ten years on polyoxometalates, or polyoxoanions. This is an immense family of compounds made up of transition metal ions in their highest oxidation state and oxo ligands. The continuous progress of computers in general, and quantum chemistry software in particular, has enabled a number of topics in polyoxometalate chemistry to be studied from the electronic structure of the most representative polyoxometalate, the so-called Keggin anion, to the factors governing the inclusion complexes and the magnetism in reduced complexes.
TL;DR: Using the TDLDA method, this paper investigated how the polarizability of the d electrons of the gold atoms influences the electronic and optical properties of metallic nanoshells and showed that a polarizable jellium background can introduce a significant shift of the plasmon resonances.
Abstract: Using the TDLDA method, we investigate how the polarizability of the d electrons of the gold atoms influences the electronic and optical properties of metallic nanoshells. It is shown that a polarizable jellium background can introduce a significant shift of the plasmon resonances. The results of the study show that the theoretically calculated optical absorption spectra for gold nanoshells with a gold sulfide core are in excellent agreement with experimental data.
TL;DR: The pseudo–one-dimensional (psuedo-1D) conjugated electronic structure of single-walled carbon nanotubes allows them to exhibit semiconducting and metallic properties and to exhibit ballistic transport.
Abstract: The pseudo–one-dimensional (psuedo-1D) conjugated electronic structure of single-walled carbon nanotubes (SWNTs) allows them to exhibit semiconducting and metallic properties and to exhibit ballistic transport ( [1][1] ) We show that their unique electronic structure also offers the opportunity
TL;DR: In this paper, the authors present near edge X-ray absorption spectra of manganese oxides at the Mn L2,3, Mn K, and O K edges to investigate the relative sensitivity of the edges to bonding and structure.
Abstract: We present near edge X-ray absorption spectra of manganese oxides at the Mn L2,3, Mn K, and O K edges to investigate the relative sensitivity of the edges to bonding and structure. Collectively, the spectra probe local electronic structure and intermediate range crystal structure. Spin independent full multiple scattering calculations of the Mn K edge give good agreement with data above threshold and qualitatively reproduce the prepeak that is observed for each compound. We show that the apparent prepeak for MnO is not due to p-d hybridization at the Mn atom (in accordance with symmetry principles) or quadrupolar transitions but originates from multiple scattering within the fifth shell. We present spin dependent multiple scattering calculations of the O K edge and show that this edge allows for a more direct description of the 3d states than either the Mn L edge or K edge prepeak, which are complicated by multiplet effects.
Book•
01 Jan 2003
TL;DR: In this paper, the authors present a model for atomic, molecular, and crystal structure and approximate separation of electronic and nuclear motion, as well as an interpretation of molecular electronic structure.
Abstract: Volume 1. Introduction. Elements of quantum mechanics. Orbital models for atomic, molecular and crystal structure. Symmetry groups and molecular structure. Second quantization and many-body methods. Approximate separation of electronic and nuclear motion. Quantum electrodynamics of atoms and molecules. Volume 2. Approximation methods. Orbital models and generalized product functions. Electron correlation. Relativistic molecular electronic structure. Electronic structure of large molecules. Computational quantum chemistry. Visualization and interpretation of molecular electronic structure. Volume 3. Response theory and propagator methods. Interactions between molecules. Molecules in different environments. Molecular electronic spectroscopy. Atomic spectroscopy and molecular vibration-rotation spectroscopy. Molecular dynamics and dynamical processes. Bulk properties.
Book•
01 Jan 2003
TL;DR: In this paper, the electronic properties of Self-Assembled Quantum Dots and their properties in self-assembled In(Ga)As/GaAs quantum Dots are discussed.
Abstract: Epitaxial Growth and Electronic Structure of Self-Assembled Quantum Dots.- Electronic Properties of Self-Assembled Quantum Dots.- Exciton Complexes in Self-Assembled In(Ga)As/GaAs Quantum Dots.- Optical Spectroscopy of Epitaxially Grown II-VI Single Quantum Dots.- Quantum-Dot Lasers.- Dephasing Processes and Carrier Dynamics in (In,Ga)As Quantum Dots.- Solid-State Cavity-Quantum Electrodynamics with Self-Assembled Quantum Dots.- Nonclassical Light from Single Semiconductor Quantum Dots.- Subject Index.
TL;DR: In this paper, the current situation in the theory of superconducting and transport properties of MgB 2 is reviewed and first principle calculations of the electronic structure and electron-phonon coupling are discussed and compared with the experiment.
Abstract: We review the current situation in the theory of superconducting and transport properties of MgB 2 . First principle calculations of the electronic structure and electron–phonon coupling are discussed and compared with the experiment. We also present a brief description of the multiband effects in superconductivity and transport, and how these manifest themselves in MgB 2 .
TL;DR: The TranSIESTA method is used to investigate the electrical properties of three ring phenyl‐ethynylene oligomers (OPE) and results for the electrical effect of side groups and molecular conformations of the molecules are presented.
Abstract: Our recently developed method, TranSIESTA, enables modelling of molecular electronic devices under operation conditions. The method is based on density functional theory, and calculates the self-consistent electronic structure of a nanostructure coupled to three-dimensional electrodes with different electrochemical potentials. It uses a full atomistic ab initio description of both the electrodes and the nanoscale device. The calculations reveal information about the scattering states, transmission coefficients, electron current, and non-equilibrium forces in the systems. In this paper we use the method to investigate the electrical properties of three ring phenyl-ethynylene oligomers (OPE). We present results for the electrical effect of side groups and molecular conformations of the molecules. The calculations indicate that molecular switching and negative differential conductance (NDC) are related to rotations of the middle phenyl ring.
TL;DR: The spectrum of the body-centered cubic phase shows an instability at zero temperature over a broad region of the wave vectors, indicating that this phase is highly anharmonic and can be stabilized at high temperatures by its phonon entropy.
Abstract: We constructed computer-based simulations of the lattice dynamical properties of plutonium using an electronic structure method, which incorporates correlation effects among the f-shell electrons and calculates phonon spectra at arbitrary wavelengths. Our predicted spectrum for the face-centered cubic δ phase agrees well with experiments in the elastic limit and explains unusually large shear anisotropy of this material. The spectrum of the body-centered cubic phase shows an instability at zero temperature over a broad region of the wave vectors, indicating that this phase is highly anharmonic and can be stabilized at high temperatures by its phonon entropy.
TL;DR: In this paper, a few representative cases from the field of inorganic, organometallic and bio-chemistry are presented, showing that the success of the CASSCF/CASPT2 method is critically dependent upon its judicious application, in particular upon the choice of the orbitals to be included in the reference active space.
Abstract: During the past ten years, the CASSCF/CASPT2 method has been applied with considerable success to a substantial number of problems related to the electronic spectroscopy of transition metal complexes, thus providing a definite breakthrough of ab initio quantum chemistry in this domain. This will be illustrated in the present contribution by means of a few representative cases from the field of inorganic, organometallic and bio-chemistry. Furthermore, CASPT2 results obtained for the excitation energies of the ions UO2 2+ and UO2Cl4 2- will be presented, indicating that the method is also applicable with comparable accuracy for molecules with very heavy metals (provided that relativistic effects are accounted for). We will also show that the success of the method is critically dependent upon its judicious application, in particular upon the choice of the orbitals to be included in the reference active space. A link will be made between the latter choice and the specific electronic structure of the metal—lig...