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International audience; The Crystal program for quantum-mechanical simulations of materials has been bridging the realm of molecular quantum chemistry to the realm of solid state physics for many years, since its first public version released back in 1988. This peculiarity stems from the use of atom-centered basis functions within a linear combination of atomic orbitals (LCAO) approach and from the corresponding efficiency in the evaluation of the exact Fock exchange series. In particular, this has led to the implementation of a rich variety of hybrid density functional approximations since 1998. Nowadays, it is acknowledged by a broad community of solid state chemists and physicists that the inclusion of a fraction of Fock exchange in the exchange-correlation potential of the density functional theory is key to a better description of many properties of materials (electronic, magnetic, mechanical, spintronic, lattice-dynamical, etc.). Here, the main developments made to the program in the last five years (i.e., since the previous release, Crystal17) are presented and some of their most noteworthy applications reviewed.

International audience; We revise formal and numerical aspects of collinear and non-collinear density functional theories in the context of a two-component self-consistent treatment of spin–orbit coupling. Theoretical and numerical analyses of the non-collinear approaches confirm their ability to yield the proper collinear limit and provide rotational invariance of the total energy for functionals in the local-density or generalized-gradient approximations (GGAs). Calculations on simple molecules corroborate the formal considerations and highlight the importance of an effective screening algorithm to provide the sufficient level of numerical stability required for a rotationally invariant implementation of non-collinear GGA functionals. The illustrative calculations provide a first numerical comparison of both previously proposed non-collinear formulations for GGA functionals. The proposed screening procedure allows us to effectively deal with points of small magnetization, which would otherwise be problematic for the evaluation of the exchange–correlation energy and/or potential for non-collinear GGA functionals. Both previously suggested formulations for the non-collinear GGA are confirmed to be adequate for total energy calculations, provided that the screening is achieved on a sufficiently fine grid. All methods are implemented in the Crystal program.

International audience; A noncanonical coupled perturbed Kohn–Sham density functional theory (KS-DFT)/Hartree-Fock (HF) treatment of spin–orbit coupling (SOC) is provided. We take the scalar-relativistic KS-DFT/HF solution, obtained with a relativistic effective core potential, as the zeroth-order approximation. Explicit expressions are given for the total energy through the 4th order, which satisfy the 2n + 1 rule. Second-order expressions are provided for orbital energies and density variables of spin-current DFT. Test calculations are carried out on the halogen homonuclear diatomic and hydride molecules, including 6p and 7p elements, as well as open-shell negative ions. The computed properties through second or third order match well with those from reference two-component self-consistent field calculations for total and orbital energies as well as spin-current densities. In only one case (At2–) did a significant deviation occur for the remaining density variables. Our coupled perturbation theory approach provides an efficient way of adding the effect of SOC to a scalar-relativistic single-reference KS-DFT/HF treatment, in particular because it does not require diagonalization in the two-component spinor basis, leading to saving factors on the number of required floating-point operations that may exceed one order of magnitude.

The spin-current density functional theory (SCDFT), when formulated in a basis of Pauli spinors, provides a proper theoretical framework for the study of materials in an arbitrarily oriented external magnetic field and/or upon inclusion of spin-dependent relativistic effects, such as spin-orbit coupling. The SCDFT is formulated in terms of the particle-number density $n$, the Cartesian components of the magnetization ${m}_{x},$ ${m}_{y},$ and ${m}_{z}$, the orbital-current density $\mathbit{j}$, and the three spin-current densities ${\mathbit{J}}^{x},$ ${\mathbit{J}}^{y},$ and ${\mathbit{J}}^{z}$, where each of these density variables depends on specific blocks of the density matrix. Exchange-correlation (xc) functionals within the SCDFT should therefore depend on all of these eight fundamental density variables: ${F}_{xc}[n,{m}_{x},{m}_{y},{m}_{z},\mathbit{j},{\mathbit{J}}^{x},{\mathbit{J}}^{y},{\mathbit{J}}^{z}]$, which makes their parametrization a formidable task. Here, we formulate the adiabatic connection of the SCDFT for a treatment of exact Fock exchange in the theory. We show how the inclusion of a fraction of Fock exchange in standard functionals of the (spin) DFT (either in their collinear or noncollinear versions: ${F}_{xc}[n],$ ${F}_{xc}[n,{m}_{z}]$ and ${F}_{xc}[n,{m}_{x},{m}_{y},{m}_{z}]$) allows for the two-electron potential to depend on all those blocks of the density matrix that correspond to the eight density variables of the SCDFT, in a sensible and yet practical way. In particular, in the local-density and generalized-gradient approximations of the SCDFT, the treatment of the current densities solely from the Fock exchange term is formally justified by the short-range behavior of the exchange hole. We discuss that the adiabatic coupling strength parameter modulates the two-electron coupling of the orbital- and spin-current densities with the particle-number density and magnetization. Formal considerations are complemented by numerical tests on a periodic model system in the presence of spin-orbit coupling and in the absence of an external magnetic field.

We perform a formal analysis of relativistic density functional theory for the treatment of spin-orbit coupling (SOC), noncollinear magnetization (NCM), and orbital current density (OCD). We identify specific components of the spinors (namely, those mapped onto imaginary diagonal spin-blocks of the density matrix) that arise from the SOC operator and define the OCD. We show that these pieces of the spinors only enter in the bielectronic part of the potential through the exact Fock exchange (FE) operator. The lack of FE therefore leads to a correspondingly incorrect physical description of SOC, NCM, and OCD. This analysis is complemented with an illustrative example, where we show that, while in the absence of FE, the theory fails even at reproducing the expected right-hand relationship between the NCM and OCD, its inclusion provides results that match those from a reference SOC configuration-interaction calculation.

We revise formal and numerical aspects of collinear and noncollinear density functional theory (DFT) in the context of a two-component self-consistent treatment of spin-orbit coupling (SOC). While the extension of the standard one-component theory to a noncollinear magnetization is formally well-defined within the local density approximation, and therefore results in a numerically stable theory, this is not the case within the generalized gradient approximation (GGA). Previously reported formulations of noncollinear DFT based on GGA exchange-correlation potentials have several limitations: (i) they fail at reducing (either formally or numerically) to the proper collinear limit (i.e., when the magnetization is parallel or antiparallel to the z axis everywhere in space); (ii) they fail at ensuring a quantitative rotational invariance of the total energy and even a qualitative rotational invariance of the spatial distribution of the magnetization when a SOC operator is included in the Hamiltonian; (iii) they are numerically very unstable in regions of small magnetization. All of the above-mentioned problems are here shown (both formally and through test examples) to be solved by using instead a new formulation of noncollinear DFT for GGA functionals, which we call the "signed canonical" theory, as combined with an effective screening algorithm for unstable terms of the exchange-correlation potential in regions of small magnetization. All methods are implemented in the CRYSTAL program and tests are performed on simple molecules to compare the different formulations of noncollinear DFT.

The electronic spectra up to 50,000 cm(-1) of uranyl(V) both as a bare ion, UO2(+), and coordinated with three carbonate ligands, [UO2(CO3)3]5-, are presented. Solvent effects were treated by a nonequilibrium continuum solvent model. The transition energies were obtained at the spin-orbit level using relativistic wave function based multiconfigurational methods such as the complete active space self-consistent field method (CASSCF)and the complete active space with second-order perturbation theory (CASPT2) followed by a calculation of the spin-orbit effects at the variation-perturbation level. Earlier relativistic intermediate Hamiltonian Fock space coupled-cluster calculations on the spectrum of the bare uranyl(V) ion were extended to investigate the influence of electron correlation effects on spacings between the electronic states. This study is an attempt to contribute to an enhanced understanding of the electronic structure of actinyl ions. Both spectra show transitions within nonbonding orbitals and between nonbonding and antibonding orbitals as well as charge transfers from the uranyl oxygens to uranium. The ground state in UO2(+) is found to be 2Φ(5/2u), corresponding to the σ(u)(2)φ(u)(1) configuration, while in [UO2(CO3)3]5-, it is 2Δ(3/2u), arising from the σ(u)(2)δ(u)(1) configuration. It is remarkable that the excited state corresponding to an excitation from the nonbonding δ(u) to the uranyl antibonding 3π(u)* molecular orbital is significantly lower in energy in the carbonate complex, 6623 cm(-1), than that in the bare ion, 17,908 cm(-1). The first ligand (carbonate) to metal charge-transfer excitation is estimated to occur above 50,000 cm(-1). The reported results compare favorably with experiment when available.

The 5 f 1 6 d ( t 2 g ) 1 emission spectrum of Cs 2 GeF 6 :U 4+ single crystals has been calculated using the relativistic ab initio model potential (AIMP) embedded cluster method. It consists of a series of broad, intense bands in the UV followed by broad and increasingly weaker bands in the visible and near infrared spectral range, which appear to be associated with emissions from the lowest 5 f 1 6 d ( t 2 g ) 1 excited state, 1 E u , to a number of levels of the 5 f 2 manifold. The electric dipole allowed emission of highest energy, 1 E u → 1 T 1 g , is found to have very low oscillator strength, - 0.115 × 10 - 2 ; this value is only 4% of the most intense electronic transition: 1 E u → 1 T 2 g whose electronic origin is found to be at 34 200 cm - 1 . A very large Stokes shift of 6200 cm - 1 is obtained, which should result in low luminescence quenching due to reabsorption and should favourably contribute to the emission quantum efficiency. The lifetime of the spontaneous emission from 1 E u has been calculated to be in the nanoseconds range: 33 ns.

The aim of this paper is to present the methodology of ab initio simulation in the field of photoluminescent materials using the local embedded cluster technique. In our approach the effect of the crystalline environment is introduced via ab initio embedding model potentials and the resulting hamiltonian of the perturbed cluster is treated using state-of-the-art quantum chemistry methods including a refined spin–orbit coupling treatment. The method is applied to the case study of a Bi 3+ ion embedded in a site of point symmetry S 6 of Y 2 O 3 sesquioxide. Comparison of the results obtained with two kinds of embedded clusters (a monoatomic Bi 3+ cluster and a more realistic molecular (BiO 6 ) 9− cluster) makes it possible to separate the respective parts of crystal field and molecular bonding. Both effects contribute to a marked stabilization of Bi 3+ 6s6p z versus Bi 3+ 6s6p x,y , which causes a spectacular quenching of spin–orbit effects. The strong decrease of the 6s 2 -6s6p z energy separation (10 → 4 eV) observed on embedding Bi 3+ is entirely due to the small covalent character of the mainly ionic Bi–O bond, not at all to crystal field. The lowest-lying excited states calculated in the range 4.3–5.1 eV are found to be the four components of the Bi 3+ (6s6p z ) 3 A u and 1 A u complex. The next states, above 6.9 eV, are charge transfer states corresponding to the excitation of an electron of the valence 2p band of oxygen of the ground state into the 6p z bismuth orbital. In the qualitative orbital model this allows to deduce an estimate of the position of the Bi 3+ ground state with respect to the top of the oxygen valence band: 2.6 eV.

High level (CASSCF-MRCI) ab initio calculations are used to investigate the structural, electronic and vibrational properties of the electronic ground state of thiazyl chloride (NSCl) and of the low-lying electronic states of NSCl + . A new high resolution HeI photoelectron spectrum of NSCl has been recorded in the 10–16 eV energy region. From the results of the calculations, the first band is assigned to the (1) 2 A ′ state of NSCl + . The second one corresponds to the (2) 2 A ′ and (1) 2 A ″ states which are quasi-degenerate. Despite the high resolution, the two first bands show no vibrational fine structure. For the first one, Franck–Condon analysis shows that it is due to the overlapping of two vibrational progressions involving the S–Cl stretching and the NSCl bending modes. In the case of the second band, it is explained by the highly repulsive character of the potential energy surfaces of two states of NSCl + in the Franck–Condon region of the neutral molecule. For the third band, which shows vibrational peaks, the calculation of Franck–Condon factors permits the determination of the adiabatic ionisation energy of the (3) 2 A ′ electronic state of NSCl + at 13.798 eV. Finally, the fourth band, which is due to three different ionic states with vibrational progressions, is too complicated to be assigned quantitatively.

International audience; The carbon and oxygen K-shell spectra of gaseous 2-propenal (acrolein) have been measured using the inner-shell electron energy loss spectroscopy method. Large scale ab initio configuration interaction calculations have been carried out to enable firm assignments of the observed bands. The overall shapes of the spectra are similar to previous low resolution monolayer and multilayer phases NEXAFS spectra recorded by photoabsorption of synchrotron radiation, but the spectral bands are much better resolved than the earlier ones. The spectra are dominated by excitation of π* type states and by interaction between the C=C and C=O π* orbitals.

This contribution is devoted to discussing some aspects of the part ab initio quantum chemistry can play in the study of laser materials via the local embedded cluster approach. The evolution in the applications of the method is briefly surveyed. Special focus is put on its specific capabilities with respect to those of the semi-empirical Crystal Field Theory (CFT). Two of the most recent improvements of the method are presented. One concerns the theory of ab initio model potentials for representing the effect of the environment. The other relates to new developments in the accurate treatment of spin–orbit and electronic correlation, especially for rare-earths. Preliminary results concerning the application of these methods to the concrete case of the Nd 3+ ion in lithium niobate are reported. The need to account for steric and electrostatic relaxation is pointed out. The chapter ends on some prospective views regarding the possibilities of calculating transition probabilities and investigating the influence of defects on laser properties.

International audience; Vibrational spectroscopy gives important information on the properties of ligand and metal–ligand bonds in metalloenzymes. Infrared spectroscopy is appealing for the study of metal active sites that are not amenable to Raman spectroscopy. We present a combined experimental and theoretical approach to analyze the mid- and far-IR spectra of Cu,Zn-superoxide dismutase (Cu,Zn-SOD) as a probe of the histidine ligands. This metalloenzyme provides a unique model to identify specific IR signatures of metal–histidine coordination and to study their alterations as a function of the metal (copper/zinc), the copper valence state (+I/+II), the histidine coordination mode (Nτ and Nπ) and the histidine protonation state. DFT calculations combined with normal mode descriptions from potential energy distribution calculations were performed on two slightly different cluster models. Differences in the constraints at the side chain of one histidine Cu ligand sensibly modify the geometric parameters and vibrational properties. Electrochemically induced FTIR difference spectroscopy provided mid- and far-IR fingerprint spectra of the Cu protein in aqueous media that are sensitive to the redox state of the Cu centre at the active site. Comparisons of the DFT predictions with the experimental IR modes of the histidine ligands at the Cu,Zn-SOD active site showed that useful mid-IR markers of histidine Nτ and Nπ coordination were predicted with good accuracy. The DFT analysis further demonstrated a link between the ν(C4–C5) mode frequency of His46 and the specific properties of the His46–Cu bond in Cu,Zn-SOD. A combined theoretical and experimental approach on samples in H2O and 2H2O or 15N-labelled samples identified the contributions from the histidine side chain modes in the 669–629 cm–1 region.

Cooperative effects are known to strongly affect the geometrical, energetic and vibrational properties of hydrogen bonded systems. In particular, such effects strongly favor molecular arrangements where each molecule is simultaneously a donor and an acceptor of hydrogen bonds (HBs), regardless of the chemical nature of the monomer subunits. In the particular case of water systems, it has been shown that the more a molecule is a proton donor in HBs, the more the HBs where it is a proton acceptor are reinforced. Such a property could be at the origin of the equilibrium between the two species of hydrogen bonded water molecules in liquid water (one with a strong hydrogen bonding character, and one with a weaker one), as experimentally evidenced and as a molecular dynamic study of the small (H2O)24 cluster clearly suggests.

We present a new two-step uncontracted spin-orbit configuration interaction (CI) method which automatically accounts for spin-orbit polarization effects on multiconfigurational wave functions by selecting the single excitations having a significant spin-orbit interaction with a chosen determinantal reference space. This approach is in the line of a conventional two-step method, as a sophisticated correlation treatment in a scalar relativistic approximation is carried out in the first step. In the second step, we define a model space which includes a set of reference configurations able to represent all the wanted states along with singly excited configurations selected with the spin-orbit (SO) operator. We then exploit the first-step calculation in order to include correlation effects via an effective Hamiltonian technique and diagonalize the full matrix on the determinantal basis. The method combines the advantages of both one-step and conventional two-step SO–CI methods; it intends to treat efficiently the cases where both relativity and extended CI treatments are needed. The new code EPCISO is tested on the spin-orbit splitting of the 2P electronic ground state of the thallium atom which, in spite of its very simple electronic structure is a well-known difficult case study for SO–CI methods. The EPCISO code yields results in excellent agreement with the experimental splitting value; they are compared to those obtained using the conventional two-step CIPSO code.

Ab initio computations at the MP2 level on five dimers and five cyclic trimers, drawn from water, ammonia, and formaldehyde are presented. Trimers have been drawn to present cyclic X–H---Y patterns. Particular attentions have been devoted in analyzing the energetic contributions resulting from cooperative effects in the trimer binding energies (BEs) and in analyzing the trends of several parameters from monomers to dimers and from dimers to trimers [in particular, the trends of the R(X–H) bond lengths, of the R(X---Y) distances, of the δvXH shifts in the vXH stretch vibrational frequencies, and of the electronic density ρc value at the XH---Y axis critical point when it exists]. The results have exhibited that cooperative effects represent from 10% to 16% of the trimer BEs and that they reinforce, from dimers to trimers, the trends observed for the above parameters from monomers to dimers. In particular, for “typical” X–H---Y HB (i.e., where X and Y atoms correspond to oxygen or nitrogen atoms), R(X–H) bo...

The carbon and nitrogen K-shell excitation spectra of gaseous pyridine and pyridazine were recorded using the electron-energy loss spectroscopy under electric-dipole conditions (2 keV, small angle) with a resolution of 0.2 eV. Ab initio Configuration interaction calculations in the frame of the equivalent core model were performed in order to help in the assignment of the spectral features. The spectra are dominated by the transitions to the 1π* and σ* type orbitals. The C1s spectra of both molecules are close to that of benzene: The intensity of Rydberg transitions are enhanced by an important valence σC–H* character; the 1s→3π* transition is mixed with double excitations and give rise to several states, some of them lying above the ionization thresholds. Finally, the N1s spectra of both molecules are similar to the s-triazine one.

The electronic and vibrational properties of CN − adsorbed on M metals (M=Pt, Ag, Au) have been studied through different quantum calculations (SCF, MCSCF and DFT) of the MCN − and MNC − molecular ions; moreover the IR and Raman intensities have been computed for each vibrational frequency. All these theoretical results allow us to have a better understanding of the spectra obtained by SFG (or DFG) experiments on Pt, Ag and Au electrodes which exhibit two resonances with Pt and an unique one with Ag and Au.

An intramolecular potential term (expressed as a series expansion in terms of internal coordinates) has been introduced in the water many-body model TCPE to estimate the water cluster OH stretch vibrational spectrum. Model parameters are derived from experimental results on (H 2 O) n clusters ( n =1–5). OH stretch vibrational spectra of three water hexamers computed with TCPE are in good agreement with available ab initio computations, and, as compared to experimental data, TCPE results also agree with the assignment of the experimental benzene–(H 2 O) 6 OH spectrum to a structure where water adopts a three-dimensional cage like structure π-hydrogen bonded to benzene.

The properties of four water tetramers have been investigated using ab initio computations at the MP2/6-311+G(2d,2p) level. The four tetramers correspond to various molecular arrangements. The computations showed that, with respect to the water dimer, a significant reinforcement of the hydrogen bonds occurs due to cooperative effects when water molecules adopt a pattern where they are simultaneously donor and acceptor of a hydrogen bond. This is consistent with an interpretation of hydrogen bonding in terms of charge-transfer phenomena in the hydrogen bond region and suggests that the origin of a part of the cooperativity occurring in water aggregates arises from cooperative charge-transfer phenomena. Analysis of the intermolecular interaction energies, carried out by both the ab initio supermolecule approach and the SIBFA molecular mechanics procedure, showed the inductive effects to be mainly responsible for the tetramer nonadditive effect.

Three flexible models (PW, CMP and TCPE) are presented to study interactions occurring in water clusters. The total interaction energy is decomposed into five terms; repulsive, charge–charge, intramolecular relaxation, polarization, and hydrogen bonding. The parameters of the first three terms are the same for all of the three models. The polarization term is taken as a classical molecular many-body polarization potential for the CMP and TCPE models, while nonpairwise effects are omitted in the PW model. As nonpairwise effects occurring in water clusters greater than the dimer have a topological origin, such effects are introduced in the hydrogen bonding term of the TCPE model. Parameters of the three models are derived from ab initio calculations at the MP2/6-311+G(2df,2p) level on three water dimer structures and the cyclic water trimer. Application of the three models to water clusters (H2O)n from n=3 to 20 exhibits that the nonpairwise effects in such clusters represent about 20% of their total bindin...

A high-resolution near infrared spectrum of the CrCl radical has been recorded in thermal emission with Fourier transform techniques in the interval from 6 900 cm−1 to 11 500 cm−1. Two dominating band systems have been found in this region; (1) The A 6Σ+→X 6Σ+ system, analyzed in the present work, consisting of the (0,0), (0,1), (1,0), (2,0), and (3,0) bands, the (0,0) band being located at around 9450 cm−1; (2) the B 6Π→X 6Σ+ system, with a band interpreted as (0,0), located between 8700 cm−1 and 9000 cm−1, overlapping the (0,1) band of the A 6Σ→X 6Σ+ system. A rotational analysis of the A 6Σ+→X 6Σ+ system has been carried out, and the following principal parameters (cm−1) have been derived: X 6Σ+: ωe=396.6621, Be=0.167 587 3, De=1.1835⋅10−7; A 6Σ+: ωe=379.39, Be=0.156 51. Local perturbations in the A 6Σ+ (v=0,1) levels have been attributed to interactions with the B 6Π (v=1,2) levels. In the present work, we have constrained the investigations on the B 6Π→X 6Σ+ system to the verification that the lower ...

The three-dimensional potential energy functions for the two components of the X2П ground state of HCSi isomer have been determined by multi-reference contracted CI calculations. These potentials have been used in beyond Born-Oppenheimer variational calculations of the ro-vibronic energy levels including the couplings of rotation-vibration, the electron spin and the electronic angular momenta: band origins are given up to 4000 cm−1. Selected MRCI calculations on the HSiC isomer have shown that the more stable structure of this isomer is a bent 2A′ , stabilized however by a small barrier of only 2800 cm1. The geometry of the saddle point between the two isomers has been located.

The [math] and [math] cations have been investigated at ab initio high quality electronic correlation level of theory and with density functional methods. Equilibrium structures, vibrational frequencies and relative energies have been determined for cyclic and linear isomers. We have found that the homoatomic [math] and [math] are unambiguously cyclic while the heteroatomic systems present very low barriers to linearity.

Dans ce travail, nous avons calcule par les methodes de fonctionnelle de la densite, les geometries d'equilibre, les moments dipolaires et les frequences vibrationnelles des plus bas etats electroniques des cations silico carbones a quatre atomes, correspondant aux conformations geometriques les plus probables. Pour C 4 + , les geometries lineaire et cyclique sont quasi degenerees. SiC 3 + et Si 4 + possedent une structure cyclique dans leur etat fondamental, Si 2 C 2 + est lineaire, tandis que Si 3 C + possede une structure T symetrique avec un atome central de carbone. L'analyse comparative de la repartition de la charge atomique pour les clusters a trois et quatre atomes fournit un schema coherent qui permet de comprendre la structure geometrique des etats fondamentaux. Enfin, nous presentons quelques regles generales concernant la reactivite des atomes de silicium.

International audience; We present a revised version of the water many-body model TCPE [M. Masella and J.-P. Flament, J. Chem. Phys.107, 9105 (Year: 1997)], which is based on a static three charge sites and a single polarizable site to model the molecular electrostatic properties of water, and on an anisotropic short range many-body energy term specially designed to accurately model hydrogen bonding in water. The parameters of the revised model, denoted TCPE/2013, are here developed to reproduce the ab initio energetic and geometrical properties of small water clusters (up to hexamers) and the repulsive water interactions occurring in cation first hydration shells. The model parameters have also been refined to reproduce two liquid water properties at ambient conditions, the density and the vaporization enthalpy. Thanks to its computational efficiency, the new model range of applicability was validated by performing simulations of liquid water over a wide range of temperatures and pressures, as well as by investigating water liquid/vapor interfaces over a large range of temperatures. It is shown to reproduce several important water properties at an accurate enough level of precision, such as the existence liquid water density maxima up to a pressure of 1000 atm, the water boiling temperature, the properties of the water critical point (temperature, pressure, and density), and the existence of a "singularity" temperature at about 225 K in the supercooled regime. This model appears thus to be particularly well-suited for characterizing ion hydration properties under different temperature and pressure conditions, as well as in different phases and interfaces.

The predissociation or dissociation of selected vibronic levels of the X 2 Π, A 2 Π, and B 2 Σ + states of the COS+ ions has been studied experimentally. The product state distribution has been probed by photoabsorption of the synchrotron radiation in the 13.5–16.5 eV range and threshold photoelectron-photoion coincidence spectroscopy. Ab initio calculations have been performed to model the potential energy surfaces of the X 2 Π, A 2 Π, and B 2 Σ + electronic states and also of the lowest energy 4Σ− state. This latter is coupled by spin-orbit to X 2 Π and is confirmed to be responsible of the predissociation in the A − X Franck-Condon gap. In the A − X Franck-Condon energy gap the predissociation mechanism by 4Σ− is not statistical and favours the production of vibrationally excited CO (v″) with maximum probability for the highest energy accessible levels. It involves also a highly effective transfer into rotational motion. For the A 2 Π state, there is internal conversion to X 2 Π followed by predissociation to the lowest limit and, for the levels above the second limit, the predissociation by 4Σ− is in competition with direct dissociation of X 2 Π to the second limit. The B 2 Σ + state also undergoes internal conversion to X 2 Π followed by dissociation to the second limit and predissociation by 4Σ− to the first limit.

The vibrational properties of CN– pseudohalide ions adsorbed on a Pt(110) single-crystal electrode in aqueous neutral solution are studied using in situ VIS–IR sum frequency generation (SFG) and compared to theoretical results obtained from density functional theory (DFT) calculations on PtNC– and PtCN– molecular ions. As observed previously on a polycrystalline electrode, the adsorption behaviour of both ions depends drastically on the electrode potential and on the immersion potential in a CN–-containing solution. When the electrode is immersed at negative potential, two absorption bands are detected in the spectral range of the CN– stretching vibration modes on a surface site. The first resonance at 2070 cm–1 is already observed at –1.4 V (Ag/AgCl), in the hydrogen evolution potential region, with an initial potential tuning rate of 20 cm–1. A second narrow resonance, peaking at 2150 cm–1, starts growing at –0.6 V (Ag/AgCl). The occurrence of two resonances, corresponding to N-bound and C-bound CN– species, is clearly evidenced for a single-crystal electrode, and appears as a genuine property of the system, not a side effect induced by surface defects. The polycrystalline structure and the defects influence the shape, the position and the width of the resonances, not the basic spectroscopic properties of the system. This result is further supported by new density functional calculations of the vibrational properties of the PtCN– and PtNC– molecular ions.

International audience; The chloromethane cation and dication have been studied using the complete active space self-consistent field method followed by a multireference perturbative configuration interaction. The 2E ground state of CH3Cl presents a weak Jahn-Teller distortion, the 2A' and 2A" components being separated by only 3.4 kcal/mol with very similar geometries. Both states are equilibrium structures. Contrary to previous calculations, the lowest singlet and triplet states of CH3Cl++ are calculated to be stable. While the 3A2 state keeps the neutral C3v symmetry, the 1E singlet state shows a large Jahn-Teller effect, with a splitting of 32.7 kcal/mol in favor of the 1A' state, which is the ground state of the molecule. The planar 1A' state of CH2Cl++ is found to be the most stable isomer, lying 41.4 kcal/mol below the corresponding state of CH3Cl++. The 3A" state, which lies 22.59 kcal/mol above the 1A' state, has a nonplanar Cs-symmetry geometry. Finally, the CH3Cl++ (1A') → CH2ClH++ (1A') isomerization takes place via a C1-symmetry transition state, with an energy barrier of 32.85 kcal/mol.

International audience; The vibrational structure of the K-shell O1s → π∗ of acenaphthenequinone C(12)H(6)O(2) and its halogenated compound C(12)H(2)Br(2)Cl(2)O(2) has been simulated using an entirely ab initio approach. For both molecules, analysis of the calculated Franck-Condon factors confirm without ambiguity that, contrary to initial claims, the C-H stretching modes are not modified in the core states and are not excited. For C(12)H(6)O(2), the vibrational fine structure appears to be mainly due to three modes, involving C=O∗ asymmetric stretch and in-plane ring deformation modes, due to the symmetry breaking of the core state. For C(12)H(2)Br(2)Cl(2)O(2), the vibrational excitation arises essentially from the C=O∗ asymmetric stretch, with numerous secondary peaks arising from hot and combination bands. For both molecules, these bands are probably responsible for the asymmetry deduced in the experimental fits using a unique Morse potential and initially assigned to anharmonic effects.

Vibrations of the metal active site of the Cu,Zn-superoxide dismutase enzyme were analyzed by far-infrared difference spectroscopy and theoretical normal mode calculation. Both electrochemically triggered Cu(I) and Cu(II) redox states show well-defined infrared vibrational modes, notably modes of the histidine ligands, the Cu(II)-His(61)-Zn(II) bridge and of the water pseudo-ligand.

International audience; issociations of the ethyne dication following its production by photoionization in the photon energy range of 35-65 eV have been investigated by the photoelectron-ion-ion coincidence technique using both synchrotron radiation and laboratory light sources. New quantum mechanical calculations identify and locate the electronic states of the molecular dication in this energy range and show that the dissociation products are formed in their ground states by heterogeneous processes. Five reaction channels leading to three molecular fragments have been - identified and are interpreted as sequential processes, several faster than fragment rotation and one possibly involving dissociation of CH+ to H+ with a lifetime of the order of 25 fs.

12 pages; International audience; In this work, we investigate the solvation of tetravalent thorium Th(IV) in aqueous solution using classical molecular dynamics simulations at the 10 ns scale and based on polarizable force-field approaches, which treat explicitly the covalent character of the metal−water interaction (and its inherent cooperative character). We have carried out a thorough analysis of the accuracy of the ab initio data that we used to adjust the force-field parameters. In particular, we show that large atomic basis sets combined with wave function-based methods (such as the MP2 level) have to be preferred to density functional theory when investigating Th(IV)/water aggregates in gas phase. The information extracted from trajectories in solution shows a well-structured Th(IV) first hydration shell formed of 8.25 ± 0.2 water molecules and located at about 2.45 ± 0.02 Å and a second shell of 17.5 ± 0.5 water molecules at about 4.75 Å. Concerning the first hydration sphere, our results correspond to the lower bounds of experimental estimates (which range from 8 to 12.7); however, they are in very good agreement with the average of existing experimental data, 2.45 ± 0.02 Å. All our results demonstrate the predictable character of the proposed approach, as well as the need of accounting explicitly for the cooperative character of charge-transfer phenomena affecting the Th(IV)/water interaction to build up reliable and accurate force-field approaches devoted to such studies.

Ab initio calculations have been carried out in order to assign the bands observed in the carbon and oxygen K-shell spectra of gaseous tetrahydrofuran (THF), measured using inner-shell electron energy loss spectroscopy (ISEELS). The good agreement between the theoretical and the measured spectra allows us to re-assign precisely most of the peaks. The ionisation energies are calculated for the first time and found to be consistent with a quantum defect analysis of the core excitation energies. The calculated spectra for the C 2 v , C 2 and C s geometries of the molecule show very small differences. Thus, K-shell spectroscopy cannot be used to solve the controversy on the geometry of THF.

International audience; The first ab initio calculations (vertical energies and oscillator strengths) are reported for the neutral electronic transitions of isoprene (2-methyl-1,3-butadiene), CH(2)CHC(CH(3))CH(2). The VUV photoabsorption spectroscopy of the molecule is presented in the energy range 4.6 to 10.8 eV (270-125 nm) with the highest resolution yet reported above 6.05 eV, revealing new spectral features. Valence and Rydberg transitions have been assigned in accordance with the theoretical results and the associated vibronic series have been analysed. The absolute photoabsorption cross sections at energies below 6.89 eV have been used to calculate the photolysis lifetime of isoprene in the upper stratosphere (20-50 km). Electron energy loss spectroscopy (EELS) measurements have enabled further photoabsorption cross sections to be derived in the range 9-28 eV. The first ab initio calculations have been carried out to determine excitation energies to the lowest energy ionic states of isoprene. The calculations are compared with the He(i) photoelectron spectrum (8 to 17 eV) and new vibrational structure is observed in the first photoelectron band.

15 pages; International audience; The electronic spectra of the 5f2 isoelectronic actinide compounds U4+, NpO2+, and PuO22+ have been investigated theoretically both in gas phase and in solution. In the latter case the solvent was modelled by a saturated first hydration sphere, five water molecules for NpO2+, and PuO22+ and eight for U4+, and a continuum model describing the remaining solvent. The transition energies and oscillator strengths were obtained at the spin-orbit level using the relativistic wave function based multi-configuration methods CASPT2 (complete active space with second-order perturbation theory) and MRCI+DC (Davidson corrected multi-reference configuration interaction), followed by a spin-orbit CI based on a dressed effective spin-orbit Hamiltonian. This study is an attempt to contribute to an enhanced understanding of the electronic structure of tetravalent actinide ions and actinyl (V) and (VI) ions. The spin-orbit MRCI and spin-orbit CASPT2 transitions energies have been compared for the bare ions, leading us to the conclusion that the spin-orbit CASPT2 approach is reasonably accurate and can be used with confidence for the calculation of the hydrated species. The first hydration sphere and the bulk solvent lift degeneracies, but the effect on the transition energies is fairly small for the two actinyl ions, while it is larger, up to several thousands of wave numbers for U4+. The calculations allowed us to make assignments of the experimentally observed absorption spectra for all species. The computed transition energies and intensities compared favourably with experiment.

International audience; Recent reports on proteins and related models show that vibrational spectroscopy in the far-infrared domain is a promising technique to characterize metal sphere coordination in proteins. The low-frequency modes are however complex, and there is a need to develop the analysis of metal sites by means of quantum chemical calculations as a support for useful interpretation of the far-IR data. In this study, we determined vibrational properties for systems containing CuII−N(Imidazole) interactions present in many biological complexes by means of quantum chemical calculations and confronted the normal mode description with available experimental data. Analysis of the [Cu(histamine)]2+ complex led us to conclude that the anharmonic contributions are negligible in the far-IR domain. Geometry optimizations and vibrational frequency calculations of [Cu(hm)]2+ and [Cu(hm)2(ClO4)2] complexes were compared using various hybrid DFT functionals and basis sets. These investigations stressed the need of potential energy distribution calculations (PED) to assign the vibrational modes, to obtain an overall description of the vibration modes, and to efficiently compare the methods. Comparison of calculation methods with the B3LYP/6-31+G(d,p) and B3LYP/6-311+G(2d,2p) methods and with available experimental data showed that the B3LYP/6-31G(d,p) level of theory provides accurate predictions of the normal mode frequencies and assignments. These comparisons also enlighten that theoretical investigations of 2H- and 65Cu-labeled [Cu(hm)2(ClO4)2] complexes give with a very good accuracy the band shifts of the labeled copper−histamine derivatives. The theoretical calculations combined with experimental data allowed us to predict and calculate with good accuracy the values and assignments of the low-frequency IR modes, notably those involving metal contribution.

8 pages; International audience; In order to assess the accuracy of a recently adjusted relativistic energy-consistent small-core pseudopotential for uranium, the U5+ (5f1 subconfiguration) spin-orbit splitting as well as the fine structure of the U4+ (5f2 subconfiguration) spectrum have been calculated. The pseudopotential has been adjusted to four-component all-electron data, i.e., at the multiconfiguration Dirac-Hartree-Fock level using the Dirac-Coulomb Hamiltonian with a Fermi nucleus charge distribution and perturbatively including the Breit interaction. Its performance in a dressed effective Hamiltonian spin-orbit configuration interaction framework is compared to that of an older scalar-relativistic Wood−Boring adjusted pseudopotential, supplemented by a valence spin-orbit term, as well as to all-electron calculations using the Douglas-Kroll-Hess Hamiltonian. Electron correlation is accounted for by the multireference configuration interaction method with and without the Davidson correction and with different frozen-orbital spaces. Our best calculations show satisfactory agreement with experimental data; i.e., the mean absolute (relative) deviations amount to 183 (2.4%) and 948 cm-1 (5.1%) for the U5+ and the U4+ fine-structure energy levels, respectively. Even better agreement, comparable to the one for rigorous highly correlated four-component all-electron data, is obtained in intermediate Hamiltonian Fock-space coupled-cluster calculations applying the new pseudopotential.

The electronic spectra up to 50,000 cm(-1) of uranyl(V) both as a bare ion, UO2(+), and coordinated with three carbonate ligands, [UO2(CO3)3]5-, are presented. Solvent effects were treated by a nonequilibrium continuum solvent model. The transition energies were obtained at the spin-orbit level using relativistic wave function based multiconfigurational methods such as the complete active space self-consistent field method (CASSCF)and the complete active space with second-order perturbation theory (CASPT2) followed by a calculation of the spin-orbit effects at the variation-perturbation level. Earlier relativistic intermediate Hamiltonian Fock space coupled-cluster calculations on the spectrum of the bare uranyl(V) ion were extended to investigate the influence of electron correlation effects on spacings between the electronic states. This study is an attempt to contribute to an enhanced understanding of the electronic structure of actinyl ions. Both spectra show transitions within nonbonding orbitals and between nonbonding and antibonding orbitals as well as charge transfers from the uranyl oxygens to uranium. The ground state in UO2(+) is found to be 2Φ(5/2u), corresponding to the σ(u)(2)φ(u)(1) configuration, while in [UO2(CO3)3]5-, it is 2Δ(3/2u), arising from the σ(u)(2)δ(u)(1) configuration. It is remarkable that the excited state corresponding to an excitation from the nonbonding δ(u) to the uranyl antibonding 3π(u)* molecular orbital is significantly lower in energy in the carbonate complex, 6623 cm(-1), than that in the bare ion, 17,908 cm(-1). The first ligand (carbonate) to metal charge-transfer excitation is estimated to occur above 50,000 cm(-1). The reported results compare favorably with experiment when available.

International audience; Ab initio Configuration Interaction calculations have been carried out in order to assign the bands observed in the carbon and oxygen K-shell spectra of gaseous acetic acid, measured using the inner-shell electron energy loss spectroscopy (ISEELS) method with better energy resolution than in previous studies. The good agreement between the theoretical and the measured spectra allows us to assign precisely most of the peaks, especially for the Rydberg states. Some of them have been shown to have strong valence character. The lowest energy band at the carbon edge is assigned to the transitions 1sC1 --> 3p[pi]/[sigma]*(C1-H) and 1sC1 --> [pi]*(C2-O2). Simple Franck-Condon calculations, based on the linear coupling approximation, were performed in order to reproduce the vibrational structure observed for the first time in the oxygen and carbon core excited species as well as in the previously measured X-ray photoelectron spectroscopy spectra of the core ionised molecule. Finally, the calculated structural parameters of the core states of acetic acid match well those of the corresponding valence states of their Z + 1 molecules, as predicted by the equivalent core approximation. However, significant differences between the geometry of the 1sC1 --> [pi]*(C2-O2) state and the CH3NOOH ground state are obtained.

9 pages; International audience; We discuss the accuracy of density functional theory (DFT) in the gas phase for the water-exchange reactions in the uranyl(VI) aqua ion taking place both in the electronic ground state and in the first excited state (the luminescent 3Δg state). The geometries of the reactant and intermediates have been optimized using DFT and the B3LYP functional, with a restricted closed-shell formalism for the electronic ground state and either an unrestricted open-shell formalism or the time-dependent DFT method for the 3Δg state. The relative energies have been computed with wave-function-based methods such as Møller–Plesset second-order perturbation theory, or a minimal multireference perturbative calculation (minimal CASPT2); coupled-cluster method (CCSD(T)); DFT with B3LYP, BLYP, and BHLYP correlation and exchange functionals; and the hybrid DFT−multireference configuration interaction method. The results obtained with second-order perturbative methods are in excellent agreement with those obtained with the CCSD(T) method. However, DFT methods overestimate the energies of low coordination numbers, yielding to too high and too low reaction energies for the associative and dissociative reactions, respectively. Part of the errors appears to be associated with the amount of Hartree–Fock exchange used in the functional; for the dissociative intermediate in the ground state, the pure DFT functionals underestimate the reaction energy by 20 kJ/mol relative to wave-function-based methods, and when the amount of HF exchange is increased to 20% (B3LYP) and to 50% (BHLYP), the error is decreased to 13 and 4 kJ/mol, respectively.

nate, with higher resolution than in the previous studies. They are interpreted with the aid of ab initio configuration interaction calculations. The spectrum at the C 1s edge is dominated by an intense * band. The calculated chemical shift due to the different chemical environment at the carbon 1s edge calculated is in agreement with the experimental observations within a few tenths of an eV. The transition energies of the most intense bands in the C 1s excitation spectrum are discussed at different levels of calculations. In the nitrogen 1s excitation spectrum the most intense bands are due to Rydberg-valence transitions involving the * -type molecular orbitals, in agreement with the experiment. This assignment is different from that of extended Huckel molecular orbital calculations. The geometries of the core excited states have been calculated and compared to their equivalent core molecules and benzene.

Ab initio study of excitation energies and oscillator strengths for absorption towards the (3)P(1) and (1)P(1) states of the Bi(3+) ion has been performed for the Bi(3+) ion in gas phase and as a dopant of the cubic elpasolite Cs(2)NaYCl(6) and the yttria Y(2)O(3) crystal using the ab initio embedded-cluster method. The ground and excited states were computed with a relativistic spin-orbit configuration interaction approach suited for heavy elements. Electron correlation was treated in the scalar relativistic scheme with perturbative, variational, and coupled-cluster methods. Intermediate coupling is included via an effective-Hamiltonian based spin-orbit configuration interaction approach. Small-core (60 electrons) and large-core (78 electrons) relativistic effective core potentials (ECPs) have been used to describe the bismuth ion. The best match with experiment was obtained with the small-core ECP. The accuracy of excitation energies strongly depends on the electron correlation method used. The agreement between experimental data and the results obtained using second-order multiconfigurational perturbation theory is greatly improved with the shifted zeroth-order Hamiltonian proposed by Ghido et al. [Chem. Phys. Lett. 396, 142 (2004)]. Although quite time consuming, coupled-cluster and variational methods yield good agreement with experimental data. The first absorption band recorded for the doped elpasolite crystal is positioned with an excellent accuracy while the computed energy of the second absorbing manifold is in poorer agreement with experimental data. This suggests that interactions with neglected close-lying excited states with a ligand-to-metal charge transfer character may be significant. Calculations of the spectrum of Bi(3+) doping yttria in both the S(6) and C(2) site symmetries indicate that the absorbing manifold arises from electronic excitations localized on the Bi(3+) doping ion with main triplet 6s6p character. Our results predict the first absorbing peak to lie about 0.5 eV lower for the S(6) sites than for the C(2) site, thus attributing the violet and the green emission wavelengths to the S(6) and C(2) sites, respectively. A subsequent study of Stokes shift and emission wavelength should hopefully lead to a final assignment of the measured excitation spectra.

Electronic state spectroscopy of CH3COOH has been investigated using Vacuum UltraViolet (VUV) photo-absorption spectroscopy in the energy range 3.5-10.6 eV. The availability of a high-resolution photon beam (similar to 0.075 nm) has allowed detailed analysis of the vibrational progressions and allowed us to propose, for the first time, new assignments for several Rydberg series. Excited states located in the 10-14 eV region have been studied for the first time. The VUV photo-absorption spectrum is compared with the electron energy loss spectrum (EELS) recorded in dipolar transition mode (100 eV incident energy, similar to 0 degrees scattering angle) in the 5.0-14 eV energy loss range. A He(l) photoelectron spectrum has also been recorded from 10.5 to 13 eV and compared to earlier low resolution works. A new value of (10.657 +/- 0.002) eV for the ground ionic state adiabatic ionisation energy is proposed. All spectra presented in this paper represent the highest resolution data yet reported for acetic acid. New ab initio calculations help in the assignment of the spectral bands. (c) 2005 Elsevier B.V. All rights reserved.

International audience; Ab initio configuration interaction calculations have been carried out in order to assign the bands observed in the carbon K-shell spectrum of gaseous cyclopropane, measured using the inner-shell electron energy loss spectroscopy (ISEELS) method. Simple Franck-Condon calculations, based on the linear coupling approximation, were performed in order to reproduce the observed vibrational structure. The good agreement between the theoretical and the measured spectra allows to assign precisely most of the peaks. The spectrum is dominated by an intense band, corresponding to the 1s→σ∗(CC)(1a2') transition, with large vibrational excitation. This is explained by the trimethylenic equilibrium geometry of this core state, very different from the D 3h ground state structure. On the other hand, the Rydberg core-excited states and the core ion are only slightly distorted. Finally, the calculated structural and energetic parameters of the NC 2H 6 valence states match well those of the corresponding core states of C 3H 6, illustrating the validity of the equivalent core approximation.

International audience; The carbon and nitrogen K-shell spectra of gaseous s-triazine have been studied using inner-shell electron energy loss spectroscopy (ISEELS) method. Ab initio Configuration Interaction calculations have been carried out in order to assign the observed bands. As in many similar molecules, both spectra are dominated by an intense π * peak, followed by lower intensity features. At the C1s edge, the calculations show that some previous assignments made using an underestimated core ionisation energy of about 2.5 eV have to be revisited. At the nitrogen edge, the calculations predict a high intensity π* doubly excited state lying below the ionisation threshold, which could be responsible for one the most intense observable bands at 405.32 eV.