Search results for "Functional theory"
showing 10 items of 1012 documents
Ultra-nonlocality in density functional theory for photo-emission spectroscopy.
2014
We derive an exact expression for the photo-current of photo-emission spectroscopy using time-dependent current density functional theory (TDCDFT). This expression is given as an integral over the Kohn-Sham spectral function renormalized by effective potentials that depend on the exchange-correlation kernel of current density functional theory. We analyze in detail the physical content of this expression by making a connection between the density-functional expression and the diagrammatic expansion of the photo-current within many-body perturbation theory. We further demonstrate that the density functional expression does not provide us with information on the kinetic energy distribution of…
A molecular electron density theory study of the [3 + 2] cycloaddition reaction of nitrones with ketenes.
2017
The [3 + 2] cycloaddition (32CA) reaction between nitrones and ketenes has been studied within the Molecular Electron Density Theory (MEDT) at the Density Functional Theory (DFT) MPWB1K/6-311G(d,p) computational level. Analysis of the conceptual DFT reactivity indices allows the explanation of the reactivity, and the chemo- and regioselectivity experimentally observed. The particular mechanism of this 32CA reaction involving low electrophilic ketenes has been elucidated by using a bonding evolution theory (BET) study. It is determined that this reaction takes place in one kinetic step only but in a non-concerted manner since two stages are clearly identified. Indeed, the formation of the se…
How does the global electron density transfer diminish activation energies in polar cycloaddition reactions? A Molecular Electron Density Theory study
2017
Abstract The key role of the Global Electron Density Transfer (GEDT) in polar cycloaddition reactions is analysed within the Molecular Electron Density Theory (MEDT) using Density Functional Theory (DFT) calculations at the MPWB1K/6-311G(d) computational level. A comparative MEDT study of the non-polar Diels-Alder reaction between cyclopentadiene (Cp) and ethylene and the polar Diels-Alder reaction between Cp and tetracyanoethylene makes it possible to establish that the GEDT taking place in the direction of the transition state structures favours the bonding changes required for the formation of the new C C single bonds along polar cycloaddition reactions. Analysis of the reactivity indice…
Carbonyl compounds of Rh, Ir, and Mt: electronic structure, bonding and volatility
2020
With the aim to render assistance to future experiments on the production and investigation of chemical properties of carbonyl compounds of element 109, Mt, calculations of the molecular properties of M(CO)4 and MH(CO)4, where M = Rh, Ir, and Mt, and of the products of their decomposition, M(CO)3 and MH(CO)3, were performed using relativistic Density Functional Theory and Coupled-Cluster methods implemented in the ADF, ReSpect and DIRAC software suites. According to the results, MH(CO)4 should be formed at experimental conditions from the M atom with a mixture of CO and He gases. The calculated first M–CO bond dissociation energies (FBDE) of Mt(CO)4 and MtH(CO)4 turned out to be significant…
The electronic properties of an oxygen vacancy at ZrO2-terminated (001) surfaces of a cubic PbZrO3: computer simulations from the first principles
2008
Combining B3PW hybrid exchange-correlation functional within the density functional theory (DFT) and a supercell model, we calculated from the first principles the electronic structure of both ideal PbZrO(3) (001) surface (with ZrO(2)- and PbO-terminations) and a neutral oxygen vacancy also called the F center. The atomic relaxation and electronic density redistributions are discussed. Thermodynamic analysis of pure surfaces indicates that ZrO(2) termination is energetically more favorable than PbO-termination. The O vacancy on the ZrO(2)-surface attracts approximately 0.3 e (0.7 e in the bulk PbZrO(3)), while the remaining electron density from the missing O(2-) ion is localized mostly on …
Hybrid QM/MM Molecular Dynamics with AMOEBA Polarizable Embedding
2017
International audience; We present the implementation of a Born-Oppenheimer (BO) hybrid Quantum Mechan-ics/Molecular Mechanics (QM/MM) Molecular Dynamics (MD) strategy using Density Functional Theory (DFT) and the polarizable AMOEBA force field. This approach couples the Gaussian and Tinker suite of programs through a variational formalism allowing for a full self-consistent relaxation of both the AMOEBA induced dipoles and the DFT electronic density at each MD step. As the DFT SCF cycles are the limiting factor in terms of computational efforts and MD stability, we focus on the latter aspect and compare the Time-Reversible BO (TR– BO) and the Extended BO Lagrangian approaches (XL–BO) to th…
Theoretical study of the molecular structure and the stability of neutral and reduced tetracyanoethylene
2003
Abstract The molecular structure and the stability of neutral, anionic, and dianionic tetracyanoethylene (TCNE) have been studied with MP2, coupled-cluster (CC), and density functional theory (DFT) procedures. The optimized geometries are in agreement with the available experimental data, although significant deviations for the CN bond distance have been obtained at the MP2 level. The adiabatic electron affinity of TCNE calculated with the B3LYP method is overestimated by 0.32 eV. In the light of the CC results, the source of such an overestimation is suggested to lie on the theoretical approach, rather than on a too low experimental value.
A density functional investigation of thiolate-protected bimetal PdAu24(SR)18z clusters: doping the superatom complex
2009
Structure, electronic properties, optical absorption and charging properties of methylthiolate-protected bimetal PdAu(24)(SR)(18)(z) (R = Me) clusters with various charge states (-3or=zor= +3) are investigated by using density functional theory. The results are compared to properties of the well-understood singly anionic pure gold complex Au(25)(SR)(18)((-1)) [J. Akola, M. Walter, H. Häkkinen and H. Grönbeck, J. Am. Chem. Soc., 2008, 130, 3756]. The atomic structure of this all-gold complex can be written in a "divide-and-protect" way [H. Häkkinen, M. Walter and H. Grönbeck, J. Phys. Chem. B, 2006, 110, 9927] as Au(13)[Au(2)(SR)(3)](6)((-1)) where 6 v-shaped Au(2)(SR)(3) ligands protect the…
Molecular Electron Density Theory: A Modern View of Reactivity in Organic Chemistry
2016
A new theory for the study of the reactivity in Organic Chemistry, named Molecular Electron Density Theory (MEDT), is proposed herein. MEDT is based on the idea that while the electron density distribution at the ground state is responsible for physical and chemical molecular properties, as proposed by the Density Functional Theory (DFT), the capability for changes in electron density is responsible for molecular reactivity. Within MEDT, the reactivity in Organic Chemistry is studied through a rigorous quantum chemical analysis of the changes of the electron density as well as the energies associated with these changes along the reaction path in order to understand experimental outcomes. St…
Solvent-mediated assembly of atom-precise gold–silver nanoclusters to semiconducting one-dimensional materials
2020
Bottom-up design of functional device components based on nanometer-sized building blocks relies on accurate control of their self-assembly behavior. Atom-precise metal nanoclusters are well-characterizable building blocks for designing tunable nanomaterials, but it has been challenging to achieve directed assembly to macroscopic functional cluster-based materials with highly anisotropic properties. Here, we discover a solvent-mediated assembly of 34-atom intermetallic gold–silver clusters protected by 20 1-ethynyladamantanes into 1D polymers with Ag–Au–Ag bonds between neighboring clusters as shown directly by the atomic structure from single-crystal X-ray diffraction analysis. Density fun…