Functional Theory Computations (functional + theory_computation)

Distribution by Scientific Domains

Kinds of Functional Theory Computations

  • density functional theory computation


  • Selected Abstracts


    The Additive Nature of Energy Penalties in 10-Vertex nido -(Car)boranes

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005
    Farooq A. Kiani
    Abstract A structural increment system, i.e. quantitative rules that govern the relative stabilities of 10-vertex nido -boranes and-carboranes, has been determined. Density functional theory computations at the B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) level with ZPE corrections were carried out for 81 different boron hydride and carborane structures from [B10H12]2, to C3B7H11 to determine their relative stabilities. A set of eleven disfavored geometrical features that destabilize a cluster structure relative to a hypothetical ideal situation were identified and weighted by so-called energy penalties. The latter show good additive behavior and allow us to reproduce the DFT computed relative energies mostly with an accuracy of 6.0 kcal,mol,1. Some unknown 10-vertex nido- carboranes that are thermodynamically more stable than their known isomers are also identified. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]


    Inclusion of the ligand field contribution in a polarizable molecular mechanics: SIBFA-LF,

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2003
    Jean-Philip Piquemal
    Abstract To account for the distortion of the coordination sphere that takes place in complexes containing open-shell metal cations such as Cu(II), we implemented, in sum of interactions between fragments ab initio computed (SIBFA) molecular mechanics, an additional contribution to take into account the ligand field splitting of the metal d orbitals. This term, based on the angular overlap model, has been parameterized for Cu(II) coordinated to oxygen and nitrogen ligands. The comparison of the results obtained from density functional theory computations on the one hand and SIBFA or SIBFA-LF on the other shows that SIBFA-LF gives geometric arrangements similar to those obtained from quantum mechanical computations. Moreover, the geometric improvement takes place without downgrading the energetic agreement obtained from SIBFA. The systems considered are Cu(II) interacting with six water molecules, four ammonia or four imidazoles, and four water plus two formate anions. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1963,1970, 2003 [source]


    Synthesis, Structures, and Physical Properties of Benzo[k]fluoranthene-Based Linear Acenes,

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2010
    Yun-Hua Kung
    Abstract This work describes the syntheses, crystal structures, photophysical properties, and electro-chemical analyses of benzo[k]fluoranthene-based linear acenes, together with ab initio density functional theory computations on them. The molecules were prepared in generally moderate to good yields through Pd-catalyzed cycloadditions between 1,8-diethynylnaphthalene derivatives and aryl iodides. This protocol is simpler and more efficient than conventional methods. The scope and limitations of this reaction were examined. The structures of compounds 4,hb, 15,ac, 17,ab, 19,ac, and 24,je were determined by X-ray analysis; they are either bent or twisted, rather than planar. The photophysical and electrochemical properties of these cycloadducts were also investigated and compared with computational predictions based on density functional theory. [source]


    An Experimental and Theoretical Investigation of Gas-Phase Reactions of Ca2+ with Glycine

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2006
    Inés Corral Dr.
    Abstract The gas-phase reactions between Ca2+ and glycine ([Ca(gly)]2+) have been investigated through the use of mass spectrometry techniques and B3-LYP/cc-pWCVTZ density functional theory computations. The major peaks observed in the electrospray MS/MS spectrum of [Ca(gly)]2+ correspond to the formation of the [Ca,C,O2,H]+, NH2CH2+, CaOH+, and NH2CH2CO+ fragment ions, which are produced in Coulomb explosion processes. The computed potential energy surface (PES) shows that not only are these species the most stable product ions from a thermodynamic point of view, but they may be produced with barriers lower than for competing processes. Carbon monoxide is a secondary product, derived from the unimolecular decomposition of some of the primary ions formed in the Coulomb explosions. In contrast to what is found for the reactions of Ca2+ with urea ([Ca(urea)]2+), minimal unimolecular losses of neutral fragments are observed for the gas-phase fragmentation processes of [Ca(gly)]2+, which is readily explained in terms of the topological differences between their respective PESs. [source]


    Theoretical Simulation of Vibrational Sum-Frequency Generation Spectra from Density Functional Theory: Application to p -Nitrothiophenol and 2,4-Dinitroaniline

    CHEMPHYSCHEM, Issue 12 2009
    Julien Guthmuller Dr.
    Abstract The molecular orientation of adsorbed molecules forming self-assembled monolayers can be determined by combining vibrational sum-frequency generation (SFG) measurements with quantum chemical calculations. Herein, we present a theoretical methodology used to simulate the SFG spectra for different combinations of polarizations. These simulations are based on calculations of the IR vectors and Raman tensors, which are obtained from density functional theory computations. The dependency of the SFG vibrational signature with respect to the molecular orientation is presented for the molecules p -nitrothiophenol and 2,4-dinitroaniline. It is found that a suitable choice of basis set as well as of exchange-correlation (XC) functional is mandatory to correctly simulate the SFG intensities and consequently provide an accurate estimation of the adsorbed molecule orientation. Comparison with experimental data shows that calculations performed at the B3LYP/6-311++G(d,p) level of approximation provide good agreement with experimental frequencies, and with IR and Raman intensities. In particular, it is demonstrated that polarization and diffuse functions are compulsory for reproducing the IR and Raman spectra, and consequently vibrational SFG spectra, of systems such as p -nitrothiophenol. Moreover, the investigated XC functionals reveal their influence on the relative intensities, which show rather systematic variations with the amount of Hartree,Fock exchange. Finally, further aspects of the modeling are revealed by considering the frequency dependence of the Raman tensors. [source]