The use and the number of sulfonylurea herbicides have increased since the early 1980s. A good understanding of their degradation is of ecological importance, since environmental pollutants can be issued from them. It is claimed that microbial degradation and chemical hydrolysis present the main degradation pathways but photodegradation cannot be neglected. Time-dependent density functional theory has been used to help in the elucidation of the photochemical behavior of sulfonylureas.

A new synthetic approach, reacting alkaline earth metal iodides with butyllithium, lithium hydroxide, and/or lithium butoxide under salt elimination, is presented, giving access to some interesting clusters of calcium, strontium, and barium, partially in combination with lithium. The so far largest calcium cluster Li[{Ca₇(μ₃-OH)₈I₆(thf)₁₂}₂(μ₂-I)]·3THF, 4, and the new strontium compound [Sr₃I₃(OH)₂(thf)₉]I, 5, are shown to feature common building blocks of OH-capped M₃ triangles. On the basis of mainly electrostatic interactions, these clusters are not volatile. By introducing LiO^tBu, the two clusters [IM(O^tBu)₄{Li(thf)}₄(OH)] (6, M = Sr; 7, M = Ba) are prepared, 7 exhibiting volatility as an important physical property, which makes it a potential precursor for chemical vapor deposition. The structural relationship between 4, 5, 6, and 7 and their respective starting materials is shown, and possible reaction mechanisms are proposed. Exhibiting surprising and new structural motifs, the bonding modes of these clusters are investigated by the electron localization function as well as by ab initio calculations.

The adsorption of methanol on V₂O₅ and its mild oxidation to formaldehyde has been studied applying density functional theory. The model used throughout is a cluster model saturated by hydrogen atoms. It is shown that the adsorption of methanol is energetically favored if the cluster is partially reduced (i.e., protonated because of the dissociative adsorption of water). Methanol behaves as a soft base and adsorbs as a methoxonium cation. The proposed mechanism is based on two steps, the first being the dissociation of methanol to form a methoxy group on the surface. This dissociation occurs between the oxygen and the carbon atoms of methanol. Finally, for the second step, which corresponds to the desorption of formaldehyde, the calculations show that filling of the vanadyl oxygen vacancy created by formaldehyde desorption is crucial to cope with an energetically feasible reaction pathway.

The absorption and emission spectra of benzo[g,h,i]perylene, a six ring polycyclic aromatic hydrocarbon molecule (C₂₂H₁₂), embedded in a rare gas matrix are reported. Time dependent emission shows that this molecule exhibits sharp phosphorescence in the red. Supporting theoretical calculations using the recently developed time-dependent density-functional response theory formalism (TD–DFRT) allow a tentative assignment for the observed transitions. The astrochemical significance of the results is briefly discussed.

Nitrosyl metal complexes, such as the sodium nitroprusside, have attracted chemists' interest for more than 30 years. The existence of long-lived metastable states easily populated by irradiation are the principal reason for this interest. Those long-lived states are interesting either for technical applications or for fundamental research. In this work, we present a comparative density functional theory (DFT) study of the ground state of two different nitrosyl compounds:  sodium nitroprusside and cyclopentadienylnitrosylnickel(II).

The photochemical reactions of the nitroprusside and the CpNiNO complexes are explained on the basis of ΔSCF and time-dependent density functional theory (TD-DFT) calculations. Both similarities and differences in the photochemical processes are highlighted.

The photochemistry of the CpNiNO complex has been investigated using density functional theory. The whole potential energy curve along the NiNO angle coordinate is presented for the first time with both ground and metastable states, and transition states connecting the minima. The excited states of the GS, MS_I, and MS_II species have been calculated using time-dependent density functional theory. Furthermore, the structure of the excited states pertaining to the photochemistry of CpNiNO has been optimized. From these results it is shown that the backward GS � MS_II � MS_I reaction is more efficient than the forward GS → MS_II → MS_I scheme.

Vertical excitations calculated for the CrO₄^2- , MnO₄^2-  , RuO₄, CrF₆, FeCp₂, RuCp₂ and CpNiNO species are compared to experimental spectra. The results obtained from the time-dependent density-functional theory−response theory (TD-DFRT) method are compared to both previously reported ΔSCF calculations and experiment. The results show that, in general, excited states of metal oxide and metallocene compounds are well described by TD-DFRT. However, serious difficulties are met with the CrF₆ system.

In a previous work we have presented a numerical procedure for the calculation of the internal chemical hardness tensor at the molecular orbital resolution level from standard density functional calculations. In this article we describe an improvement of our method using the thermal extensions of density functional theory. Furthermore, new concepts are introduced in the orbitally resolved theory of chemical reactivity. Traditional molecular orbital theories of chemical reactivity are based only on considerations concerning the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) of molecules, supposed to describe the behavior towards electrophiles, respectively, nucleophiles. By applying our methodology to two test molecular systems, namely water and ferrocene, we show how chemical reactivity can be differentiated against hard and soft electrophiles (acids) and hard and soft nucleophiles (bases). As a by-product of the numerical algorithms being used, a self-consistent method for calculating the molecular chemical potential is also described.

The condensed Fukui functions fk of maleimide (1H-pyrrole-2,5-dione) have been calculated using a numerical integration scheme implemented in the deMon program package. The condensed functions show that soft nucleophiles interact with the α carbon atoms, whereas hard nucleophiles interact with the carbonyl carbon atoms, in accordance with the experimental evidence. The present method yields extremely few dispersed values of fk, whatever the basis sets, the numerical grids, and the exchange-correlation functionals used. Finally, the validity of the method has been successfully tested on a set of organic and organometallic molecules.

It is shown that whereas the spherical and spheroidal jellium models are inadequate to describe lithium clusters, only the ellipsoidal jellium model is adequate. The corresponding result, obtained by Yannouleas and Landman, was unpublished at the time of submission of our paper.

An hybrid functional which includes a larger amount of pure exchange has been specially designed for the description of hydrogen-only systems. Both the H abstraction by H₂ and the H+_2n+1 clusters have been investigated. Comparison with experimental values shows that the proposed functional gives dissociation energies and vibrational frequencies better than previous ab initio calculations. The results compare favorably with those obtained by a coupled clusters method [CCSD(T)], also performed in this work for sake of reference data.

The purpose of the present work was to develop a method allowing one to extract the information needed for the construction of the internal chemical hardness tensor at the molecular orbital level from standard density functional calculations. This method is based on the Janak theorem and on the extension of the Slater transition-state concept. A detailed discussion of the current ideas about the validity of the Janak theorem is presented as well as of the established relations of this subject with the ensemble V-representability problem. The internal chemical hardness tensor has been obtained for water molecule as an example system. Its structure is consistent with the criteria for the internal molecular stability.

An overview of the possibilities brought by the density functional theory to the coordination chemistry is given. The new trends in the development of the theory are outlined.

Standard ab initio and density functional calculations have been applied to the reaction O•- + H2O → [H2O2]•- → OH- + OH•. While two intermediates are found as minima on the anionic potential energy surface, neither of them is directly related to the structure of neutral hydrogen peroxide. The results of different combinations of exchange and correlation functionals are systematically compared to each other and to MP2, MP4SDTQ, and CCSD(T) calculated data. The role of the basis set and the Hartree−Fock exchange in the hybrid DFT scheme is discussed. While for the two minima a reasonable agreement between all the methods was found, the geometries of the located transition structures strongly depend on the method and basis set used.

Some properties of small Lin clusters (n up to 20) are theoretically investigated, within the density functional theory formalism. The structural properties are examined at the so-called local level of approximation. For very small clusters (n<=8), the Lin conformations which are well known from ab initio calculations are found at very low computational cost. For n>8, optimal starting geometries are generated from two growth patterns, based on the increase of the number of pentagonal subunits in the clusters by adsorption of one or two Li atoms. Several new stable structures are proposed, for which the corresponding vibrational analysis is performed for n up to 18. The study of energetic properties and stability requires the use of gradient-approximated functionals. Such functionals are used for the determination of the relative stability of these clusters. For example, we show that the icosahedral structure is the most favorable geometry for Li13, whereas this is not the case for Na13. Ionization potentials and binding energies are also investigated in regard to the size and the geometry of the clusters. Comparison with experimental results and other theoretical approaches (such as nonspherical jellium model) suggests that some combinations of gradient-corrected functionals are more adapted than others to describe Lin energetic and structural properties.

Ground�state properties of a linear hydrogen�bonded FH...NCH complex are studied by means of the ‘‘freeze�and�thaw’’ cycle of Kohn–Sham Equations with constrained electron density (KSCED) [T. A. Wesolowski and J. Weber, Chem. Phys. Lett. 248, 71, (1996)]. For several geometries of the complex, the electron density and the total energy are compared to the ones obtained by means of the standard Kohn–Sham calculations. The comparisons are made to assess the accuracy of several gradient dependent approximate kinetic energy functionals applied in the KSCED equations. It was found that the closest results to the Kohn–Sham ones were obtained with the functional whose analytical form was proposed by Perdew and Wang for exchange energy [J. P. Perdew and Y. Wang in Electronic Structure of Solids ’91, edited by P. Ziesche and H. Eschrig (Academie Verlag, Berlin, 1991), p. 11] and parametrized by Lembarki and Chermette for kinetic energy [A. Lembarki and H. Chermette, Phys. Rev. A 50, 5328 (1994)]. Around the interaction energy minimum as well as for larger intermolecular distances, the ‘‘freeze�and�thaw’’ cycle of KSCED leads to very similar potential energy surface as the standard supermolecule Kohn–Sham calculations. 

The influence of electronic and structural effects in FeCL and FeCl6 entities has been investigated through X-ray absorption spectroscopy and theoretical calculations of electronic transition energies using the MSLSD method. The relative importance of the formal oxidation degree of the metal, the metal-ligand distance, and the symmetry of the site on the energy of near-edge structures are studied. The principal effect is the stabilization of the iron 1s orbital in the ground state when the oxidation degree increases. The accuracy of the theoretical determination regarding the experimental spectra is discussed. The incidence of the same electronic parameters on the intensities of near-edge structures is also investigated through a transition cross section calculation.

In density-functional theory (DFT), Perdew, Parr, Levy, and Balduz [Phys. Rev. Lett. 49, 1691 (1982)] have shown that for all the electronic systems, the energy of the highest occupied molecular orbital (HOMO) is equal to the negative of the ionization potential. This equality is not recovered within the different approximations of the exchange-correlation functional proposed in the literature. The main reason is that the exchange-correlation potentials of various functionals used in DFT calculations decay rapidly to zero whereas they should exhibit a Coulombic asymptotic -1/r behavior. In this work we propose a gradient-corrected (GC) exchange potential with a correct asymptotic -1/r form for large values of r. The energy of the HOMO calculated with this potential is improved compared to the local-density approximation (LDA) and to the GC functionals widely used in the DFT. Our HOMO eigenvalues are compared to the optimized-potential-model eigenvalues which are the exact values for the exchange-only potential. Using the fact that the LDA satisfies the virial theorem, the exchange energy corresponding to this GC exchange potential can be calculated under a simple assumption.

Density functional calculations of ground and excited states of Li n (nle8) clusters have been performed, within two different approaches. Using a set of Kohn-Sham orbitals to construct wave functions, the calculation of the oscillator strengths of the electric dipole transitions is performed. Our results have been tested at two levels: first the necessary comparison with the experimental data, second the comparison with high level CI (MRD-CI) calculations. This last point is not a trivial challenge, because such anab initio method leads for small clusters to a highly accurate description of the electronic structure and optical absorption spectra. Finally, this is also a new test for the capability of using Kohn-Sham orbitals to construct physically meaningful wave functions. Transition energies, oscillator strengths and finally optical absorption spectra presented here are in general in reasonable agreement with the experimental data and the MRD-CI calculations. That is very promising for bigger systems, with regard to the modest computational effort (CPU time and memory size) of density functional calculations.

The possibilities and limits of the molecular orbital theory to deal with the problem of determining electronic structure of solids have been explored. A cluster model based on the charge neutrality in the solid has been used in test calculations on some III-V semiconductors and have given quite satisfactory results. Recommendations are given to widen the field of applications of this procedure.

An investigation of the influence of various gradient-corrected exchange and correlation functionals on the bond lengths and dipole moments of CO and N2O has been carried out using density functional theory. It is shown that whereas some functionals are found to be more sensitive to the basis set quality than are others, the more commonly used gradient-corrected functionals lead to properties in very good agreement with experiment provided that a sufficiently large basis set is employed.

Ab initio selfâ€�consistentâ€�field (SCF) Hartree–Fock and configuration interaction (CI) calculations have been carried out for H⁺ _2n+1 (n=1–6) clusters using a tripleâ€�zeta plus polarization basis set. Fully optimized structures and energies of H⁺ ₁₁ and H⁺ ₁₃ are presented. These structures can be thought as the addition of H₂ molecules to a deformed H⁺₉. Dissociation energies as a function of cluster size follow the pattern established experimentally by Hiraoka and Mori. Nevertheless, our energy results on the biggest clusters suffer from the lack of size consistency of CI with single and double substitutions (CISD) calculations. Analytic gradient techniques have been used to locate stationary point geometries and to predict harmonic vibrational frequencies and infrared intensities at the two levels of theory SCF (n=1–6) and CISD (n=1–4) both with tripleâ€�zeta polarizationbasis sets. Of special interest are the new vibrational modes of H⁺ ₁₁ and H⁺ ₁₃, which have no counterpart in the H⁺₉ cluster. Our predicted frequencies compare fairly well with the experimental results of Okumura, Yeh, and Lee.