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Density Functional (density + functional)
Terms modified by Density Functional Selected AbstractsA Dinuclear Double-Stranded Oxido Complex of ReV with a Bis(benzene- o -dithiolato) LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 27 2009Jorge S. Gancheff Abstract The reaction of [ReOCl3(PPh3)2] with 1,2-bis(2,3-dimercaptobenzamido)ethane (H4 - 1) in the presence of Na2CO3 in methanol under anaerobic conditions affords the dinuclear ReV oxido complex [PPh4]2[ReO(1)]2 containing two distorted square-pyramidal {ReVOS4} units bridged by the ligand strands in a double-stranded fashion. The coordinationgeometry around the metal centers is similar to the one observed for [ReO(bdt)2],. The ReS4 planes are arranged in a coplanar fashion and are not twisted around the metal,metal vector, which prevents the complex to adopt a helical structure. Luminescence studies show the presence of emission bands, which are assigned to singlet-singlet transitions exhibiting very fast decays (ca. 10 ns). Theoretical Density Functional (DFT) studies on geometry and electronic properties were performed employing the hybrid B3LYP and PBE1PBE functionals. While the general trends observed in the experimental data are well reproduced in all cases, a good agreement was obtained using PBE1PBE, in particular for the Re,S bonds. Natural Bond Orbitals (NBO) analysis indicates the presence of polarized Re,O and Re,S bonds, both of them polarized toward the non-metal. The calculation show that the molecular orbitals of the ReV are doubly degenerated, the occupied 5d orbital of rhenium lying beneath occupied sulfur-based MOs due to the rigid geometry imposed by the C,C backbone of the bis(benzene- o -dithiolato) ligands. The origin of all absorption bands is ascribed to a ligand-to-metal charge transfer (LMCT), in which occupied sulfur-based orbitals and unoccupied rhenium-centered orbitals are involved.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Theoretical Investigation on the Absorption and Emission Properties of the Three Isomers of Bis(thiocyanato)(2,2,-bipyridyl)platinum(II)CHINESE JOURNAL OF CHEMISTRY, Issue 9 2007Xiao-Ying Hu Abstract This paper presents a Density Functional or Time Dependent Density Functional (DFT/TDDFT) study of the molecular and electronic structures, optical absorption and emission spectra of three linkage isomers:bis(isothiocyanato-S)(2,2,-bipyridyl) platinum(II) ([Pt(SCN)2(bpy)]), (isothiocyanato-S)(thiocyanato-N)-(2,2,-bipy- ridyl) platinum(II) ([Pt(SCN)(NCS)(bpy)]), and bis(thiocyanato-N)(2,2,)-bipyridyl)platinum(II) ([Pt(NCS)2(bpy)]), in which different coordination ligands based on the N- and S-coordination of the thiocyanato ligands control the luminescent color. The electronic structures were studied using the B3LYP functional. Optimized geometries were compared to the experimentally observed structures. TDDFT calculation was carried out to investigate the excited singlet and triplet states. Calculations have been performed both in vacuo and in solvents, using a polarized continuum model (PCM) to account for solute-solvent interactions. Inclusion of the solvent led to a significant energy change, and as a consequence, the computed spectrum calculated in the presence of the solvent was in good agreement with the experimental determinations. The first two absorptions were found to originate from mixed platinum-SCN (or NSC) to bipyridyl-,* transitions rather than pure metal-to-ligand-charge-transfer (MLCT) transitions, whereas the higher-energy bands arose from intraligand ,,,* transitions. The stretching frequencies of C,N have been calculated both in the ground and excited states, which are relative to the charge transition during the excitation. In addition, different sizes of basis sets were also discussed in this paper. [source] Density functional and ab initio studies on structures and energies of the ground state of CrCOINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2007Joonghan Kim Abstract CrCO was studied using density functional theory (DFT) and ab initio methods. We obtained the two-dimensional potential energy surface (PES), geometry, and vibrational frequencies for CrCO in a septet state. Two minimum structures were found in the CCSD(T) calculation, including a local minimum that is a weak van der Waals (vdW) complex. All DFT methods yield only one minimum structure. We demonstrate that the bond dissociation energy (0.50 kcal/mol) and vibrational frequency (1981.1 cm,1) of CrCO calculated using CCSD(T) are in better agreement with experimental values (<1.5 kcal/mol and 1977 cm,1) than any of the reported theoretical studies. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Density functional and vibrational spectroscopic analysis of ,-caroteneJOURNAL OF RAMAN SPECTROSCOPY, Issue 6 2003S. Schlücker Abstract We report a computational study on the structural, energetic and vibrational spectroscopic characteristics of ,-carotene employing density functional theory (DFT). The optimized geometry and the complete vibrational spectrum calculated at the BPW91/6,31G* level, including infrared (IR) intensities and Raman activities, are presented. The centrosymmetric structure of ,-carotene is verified both theoretically and experimentally, by identifying a stable calculated structure with Ci symmetry and the mutually exclusive occurrence of bands in the experimental Fourier transform IR and Raman spectrum, respectively. The calculated vibrational spectra reflect the major characteristic features observed experimentally. Differences in the calculated IR intensities and Raman activities for a few dominant modes of two ,-carotene configuration isomers, the all- trans and the natural abundant (C6,C7) s- cis form, are explained qualitatively by the corresponding eigenvectors. At the level of theory employed, s- cis -,-carotene was found to be 8.8 kJ mol,1 more stable than the all- trans form. Calculations on ,-carotene model systems were performed to separate electronic from steric contributions. The higher stability of s- cis -,-carotene is explained by an energetically favored ,-ionone ring conformation, compensating for its shorter conjugation length in comparison with the all- trans form. Copyright © 2003 John Wiley & Sons, Ltd. [source] On the fragmentation pathway of the ionized enol of glycine in the gas phaseRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2001T. Marino Density functional and second-order many body perturbation approaches were used to compute the potential energy surface for the fragmentation of the ionized enol of glycine [H2NCH,=,C(OH)2]+· into water and aminoketene radical cation [H2N-HC,=,CO]+·. Two possible pathways were considered. The potential energy surfaces obtained are very similar and both predict the existence of a molecular complex in which the water is coordinated to the aminoketene moiety in two different fashions with a noticeable binding energy. The fragmentation is kinetically controlled by the step in which the molecular complex is formed from the most stable cation enol of glycine. Our quantum-mechanical data confirm the hypothesis that the ylide ion [H3NCHCOOH]+· is an intermediate in the water loss. Copyright © 2001 John Wiley & Sons, Ltd. [source] Highly Emitting Neutral Dinuclear Rhenium Complexes as Phosphorescent Dopants for Electroluminescent DevicesADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Matteo Mauro Abstract A series of neutral, dinuclear, luminescent rhenium(I) complexes suitable for phosphorescent organic light emitting devices (OLEDs) is reported. These compounds, of general formula [Re2(µ -Cl)2(CO)6(µ -1,2-diazine)], contain diazines bearing alkyl groups in one or in both the , positions. Their electrochemical and photophysical properties are presented, as well as a combined density functional and time-dependent density functional study of their geometry, relative stability and electronic structure. The complexes show intense green/yellow emissions in toluene solution and in the solid state and some of the complexes possess high emission quantum yields (,,=,0.18,0.22 for the derivatives with disubstituted diazines). In butyronitrile glass, at 77,K, due to the charge transfer character of the lowest (emitting) excited state, strong blue shift of the emission is observed, accompanied by a strong increase in the lifetime values. The highest-performing emitting complex, containing cyclopentapyridazine as ligand, is tested in a polymer-based light-emitting device, with poly(9-vinylcarbazole) as matrix, as well as in a device obtained by vacuum sublimation of the complex in the 2,7-bis(diphenylphosphine oxide)-9-(9-phenylcarbazol-3-yl)-9-phenylfluorene (PCF) matrix. This represents the first example of devices obtained with a rhenium complex which can be sublimed and is solution processable. Furthermore, the emission is the bluest ever reported for electrogenerated luminescence for rhenium complexes. [source] Reaction of H + ketene to formyl methyl and acetyl radicals and reverse dissociationsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2003Jongwoo Lee Thermochemical properties for reactants, intermediates, products, and transition states important in the ketene (CH2CO) + H reaction system and unimolecular reactions of the stabilized formyl methyl (C·H2CHO) and the acetyl radicals (CH3C·O) were analyzed with density functional and ab initio calculations. Enthalpies of formation (,Hf°298) were determined using isodesmic reaction analysis at the CBS-QCI/APNO and the CBSQ levels. Entropies (S°298) and heat capacities (Cp°(T)) were determined using geometric parameters and vibrational frequencies obtained at the HF/6-311G(d,p) level of theory. Internal rotor contributions were included in the S and Cp(T) values. A hydrogen atom can add to the CH2 -group of the ketene to form the acetyl radical, CH3C·O (Ea = 2.49 in CBS-QCI/APNO, units: kcal/mol). The acetyl radical can undergo ,-scission back to reactants, CH2CO + H (Ea = 45.97), isomerize via hydrogen shift (Ea = 46.35) to form the slight higher energy, formyl methyl radical, C·H2CHO, or decompose to CH3 + CO (Ea = 17.33). The hydrogen atom also can add to the carbonyl group to form C·H2CHO (Ea = 6.72). This formyl methyl radical can undergo , scission back to reactants, CH2CO + H (Ea = 43.85), or isomerize via hydrogen shift (Ea = 40.00) to form the acetyl radical isomer, CH3C·O, which can decompose to CH3 + CO. Rate constants are estimated as function of pressure and temperature, using quantum Rice,Ramsperger,Kassel analysis for k(E) and the master equation for falloff. Important reaction products are CH3 + CO via decomposition at both high and low temperatures. A transition state for direct abstraction of hydrogen atom on CH2CO by H to form, ketenyl radical plus H2 is identified with a barrier of 12.27, at the CBS-QCI/APNO level. ,Hf°298 values are estimated for the following compounds at the CBS-QCI/APNO level: CH3C·O (,3.27), C·H2CHO (3.08), CH2CO (,11.89), HC·CO (41.98) (kcal/mol). © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 20,44, 2003 [source] An accurate total energy density functionalINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2007Baojing Zhou Abstract We propose a new density functional for the evaluation of the total electronic energy by subtracting the Roothaan energy, i.e. the Hartree energy of the density residual, from the Hohenberg,Kohn,Sham (HKS) functional, which is normally used in self-consistent Kohn,Sham (KS) density functional theory (DFT) calculations. Because of the positive semi-definite nature of the Roothaan energy, the resulting Wang,Zhou (WZ) functional always produces a total energy lower than that from the HKS functional and usually converges to the exact total energy from below. Following the same spirit of the Zhou,Wang-, (ZW,) functional in the recently proposed orbital-corrected orbital-free (OO) DFT method (Zhou and Wang, J Chem Phys 2006, 124, 081107), we linearly mix the WZ functional with the HKS functional to allow further systematic error cancellations. The resulting Wang,Zhou-, (WZ,) functional is compared with the ZW, functional in OO-DFT calculations for systems within different chemical environment. We find that the optimal value of , for the WZ, functional is more stable than that of , for the ZW, functional. This is because the WZ functional remedies the oscillatory convergence behavior of the Harris functional and renders the direct evaluation of , for the WZ, functional more plausible in the application of the linear-scaling OO-DFT method for large systems. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] The N -particle wave function as a homogeneous functional of the densityINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 14 2007Tamás Gál Abstract It is shown that requiring consistency with the structure of the equation that determines the wave function associated to a density ,() by density-functional theory, yields the N -particle wave function as a degree-half homogeneous functional of the density, and leads to a separation A[N, ,] of N dependence (with N = ,,() d) of density functionals A[,] = A[,,, ,] for which A[,,, ,,] = , A[,, ,]; as a consequence of the linearity of quantum mechanical operators. This implies that the ground-state value of any quantum mechanical observable arises naturally as a degree-one homogeneous N -particle density functional. This general scheme for the structure of density functionals can be considered as the conceptual generalization of the Weizsäcker functional, which is the exact degree-one homogeneous one-particle kinetic-energy density functional. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Van der Waals density functional theory with applicationsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005D. C. Langreth Abstract The details of a density functional that includes van der Waals (vdW) interactions are presented. In particular we give some key steps of the transition from a form for fully planar systems to a procedure for realistic layered compounds that have planar symmetry only on large-distance scales, and which have strong covalent bonds within the layers. It is shown that the random-phase approximation of that original functional can be replaced by an approximation that is exact at large separation between vdW interacting fragments and seamless as the fragments merge. An approximation to the latter which renders the functional easily applicable and which preserves useful accuracy in both limits and in between is given. We report additional data from applications to forms of graphite, boron nitride, and molybdenum sulfide not reported in our previous communication. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Chemical bonding in ternary magnesium hydridesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2003Emilio Orgaz Abstract The electronic structure of various alkali and alkaline,earth magnesium-based hydrides was investigated in detail. These types of crystalline compounds show MgH4 or MgH6 units ordered within a light-metal framework. We investigated the nature of the chemical bonding in these units by means of quantum chemical calculations of several related clusters. The properties of the charge density of the clusters, within the framework of the theory of atoms in molecules, was analyzed. A further set of computations of the band structure of the solid hydrides was conducted using a state-of the-art density functional-based method and the mechanism of stabilization of the MgH units is discussed. It was found that the properties obtained at the molecular level correlate well with those of the solid crystals, indicating the molecular nature of the extended systems in which the units MgHx, x = 4, 6, are stabilized by means of MgH closed-shell interactions. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 150,164, 2003 [source] Revisiting N -continuous density-functional theory: Chemical reactivity and "Atoms" in "Molecules"ISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2003Morrel H. Cohen We construct an internally-consistent density-functional theory valid for noninteger electron numbers N by precise definition of a density functional that is continuous in N. In this theory, charge transfer between the atoms of a heteronuclear diatomic molecule, which have been separated adiabatically to infinity, is avoided because the hardness for fractional occupation of a single HOMO spin-orbital is negative. This N -continuous density functional makes possible a variational theory of "atoms" in "molecules" that exactly decomposes the molecular electron density into a sum of contributions from its parts. The parts are treated as though isolated. That theory, in turn, gives a deep foundation to the chemical reactivity theory provided that the hardness of entities with vanishing spin density is positive, as argued to be the case here. This transition from negative to positive hardness closely parallels the transition from the Heitler-London to the Hund-Mulliken picture of molecular bonding. [source] Interesting properties of Thomas,Fermi kinetic and Parr electron,electron-repulsion DFT energy functional generated compact one-electron density approximation for ground-state electronic energy of molecular systemsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2009Sandor Kristyan Abstract The reduction of the electronic Schrodinger equation or its calculating algorithm from 4N -dimensions to a (nonlinear, approximate) density functional of three spatial dimension one-electron density for an N -electron system, which is tractable in the practice, is a long desired goal in electronic structure calculation. If the Thomas-Fermi kinetic energy (,,,5/3dr1) and Parr electron,electron repulsion energy (,,,4/3dr1) main-term functionals are accepted, and they should, the later described, compact one-electron density approximation for calculating ground state electronic energy from the 2nd Hohenberg,Kohn theorem is also noticeable, because it is a certain consequence of the aforementioned two basic functionals. Its two parameters have been fitted to neutral and ionic atoms, which are transferable to molecules when one uses it for estimating ground-state electronic energy. The convergence is proportional to the number of nuclei (M) needing low disc space usage and numerical integration. Its properties are discussed and compared with known ab initio methods, and for energy differences (here atomic ionization potentials) it is comparable or sometimes gives better result than those. It does not reach the chemical accuracy for total electronic energy, but beside its amusing simplicity, it is interesting in theoretical point of view, and can serve as generator function for more accurate one-electron density models. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Spin states in polynuclear clusters: The [Fe2O2] core of the methane monooxygenase active siteJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2006Carmen Herrmann Abstract The ability to provide a correct description of different spin states of mono- and polynuclear transition metal complexes is essential for a detailed investigation of reactions that are catalyzed by such complexes. We study the energetics of different total and local spin states of a dinuclear oxygen-bridged iron(IV) model for the intermediate Q of the hydroxylase component of methane monooxygenase by means of spin-unrestricted Kohn,Sham density functional theory. Because it is known that the spin state total energies depend systematically on the density functional, and that this dependence is intimately connected to the exact exchange admixture of present-day hybdrid functionals, we compare total energies, local and total spin values, and Heisenberg coupling constants calculated with the established functionals BP86 and B3LYP as well as with a modified B3LYP version with an exact exchange admixture ranging from 0 to 24%. It is found that exact exchange enhances local spin polarization. As the exact exchange admixture increases, the high-spin state is energetically favored, although the Broken-Symmetry state always is the ground state. Instead of the strict linear variation of the energy splittings observed for mononuclear complexes, a slightly nonlinear dependence is found. The Heisenberg coupling constants JFe1Fe2,evaluated according to three different proposals from the literature,are found to vary from ,129 to ,494cm,1 accordingly. The experimental finding that intermediate Q has an antiferromagnetic ground state is thus confirmed. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1223,1239, 2006 [source] Parameterization of charge model 3 for AM1, PM3, BLYP, and B3LYPJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2003Jason D. Thompson Abstract We have recently developed a new Class IV charge model for calculating partial atomic charges in molecules. The new model, called Charge Model 3 (CM3), was parameterized for calculations on molecules containing H, Li, C, N, O, F, Si, S, P, Cl, and Br by Hartree,Fock theory and by hybrid density functional theory (DFT) based on the modified Perdew,Wang density functional with several basis sets. In the present article we extend CM3 to semiempirical molecular orbital theory, in particular Austin Model 1 (AM1) and Parameterized Model 3 (PM3), and to the popular BLYP and B3LYP DFT and hybrid DFT methods, respectively. For the BLYP extension, we consider the 6-31G(d) basis set, and for the B3LYP extension, we consider three basis sets: 6-31G(d), 6-31+G(d), and MIDI!6D. We begin with the previous CM3 strategy, which involves 34 parameters for 30 pairs of elements. We then refine the model to improve the charges in compounds that contain N and O. This modification, involving two new parameters, leads to improved dipole moments for amides, bifunctional H, C, N, O compounds, aldehydes, ketones, esters, and carboxylic acids; the improvement for compounds not containing N results from obtaining more physical parameters for carbonyl groups when the OCN conjugation of amides is addressed in the parameterization. In addition, for the PM3 method, we added an additional parameter to improve dipole moments of compounds that contain bonds between C and N. This additional parameter leads to improved accuracy in the dipole moments of aromatic nitrogen heterocycles with five-membered rings. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1291,1304, 2003 [source] Analysis of interaction modes in calix[4]arene,levofloxacin complexes by quantum methodsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2006Alexandrine Lambert Abstract Host,guest interactions between chiral calix[4]arenes and the antibiotic levofloxacin are analyzed on the basis of quantum mechanical calculations at the density functional (for model systems) and semi-empirical levels. The calix[4]arene macrocycle carries two (+)-isomenthyl groups attached to opposing phenyl groups at the lower rim and different substituents (R,=,H, CH3, tBu, CH2CHCH2, COCH3 and NO2) are considered at the upper rim. Nitro derivatives are expected to form ionized complexes whereas the other derivatives should form neutral complexes with a very low stability. Copyright © 2006 John Wiley & Sons, Ltd. [source] Computational study of stereoelectronic effects in fluorinated alkylamines,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2005Joseph J. Urban Abstract A systematic evaluation of the stereoelectronic effects in a series of fluorinated amine compounds has been carried out. A variety of computational methods have been employed, including molecular mechanics, semi-empirical, density functional and ab initio methods. An analysis of the natural bond orbital populations has been carried out and the effect of solvent was considered via the polarized continuum model (PCM). The results indicate a preference for conformations that result in an anti-periplanar arrangement between the nitrogen lone pair and the CX bond (XF or CF3). There are variations in geometry and natural bond orbital population, with conformation that are consistent with a stereoelectronic effect whereby electron density from the nitrogen lone pair is delocalized into the CX ,* orbital. Similar results are obtained for trifluoromethyl methylamines, although the magnitude of the stereoelectronic effect is attenuated resulting in greater expected conformational diversity for these compounds. The PCM results suggest that these preferences should persist in solution. Comparison among the computational methods used reveals that there is good agreement among the ab initio and density functional methods (at the HF/6-31,+,G(d), MP2/6-31,+,G(d), MP2/6-311,+,G(2d,p) and B3LYP/6-31,+,G(d) levels) and these methods agree well with the available experimental data for ethylmethylamine. Published in 2005 by John Wiley & Sons, Ltd. [source] Chemical bonding in zwitterionic diamino- meta -quinonoids and their isomersJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2005Tibor Höltzl Abstract Quantum chemical calculations using molecular orbital (HF) and density functional (B3LYP) methods, in conjunction with the 6-311,+,+,G(d,p) basis set, have been applied to investigate the electronic structure of a series of diamino- meta -quinonoid molecules, each containing a six-membered ring coupled with two exocyclic CO bonds situated in a meta position, along with two amino substituents (NH2 and NHR). The chemical bonding phenomena in these zwitterions and isomers where one or two hydrogens are transferred from N to O are analyzed with the aid of the atoms-in-molecules (AIM) approach. The relative energies between zwitterionic and quinonoid isomers in both neutral and ionized states also have been evaluated. Substituents exert a strong effect that in many cases changes the energy ordering. Copyright © 2005 John Wiley & Sons, Ltd. [source] Surface effects in the unitary Fermi gasLASER PHYSICS LETTERS, Issue 1 2010L. Salasnich Abstract We study the extended Thomas-Fermi (ETF) density functional of the superfluid unitary Fermi gas. This functional includes a gradient term which is essential to describe accurately the surface effects of the system, in particular with a small number of atoms, where the Thomas-Fermi (local density) approximation fails. We find that our ETF functional gives density profiles which are in good agreement with recent Monte Carlo results and also with a more sophisticated superfluid density functional based on Bogoliubov-de Gennes equations. In addition, by using extended hydrodynamics equations of superfluids, we calculate the frequencies of collective surface oscillations of the unitary Fermi gas, showing that quadrupole and octupole modes strongly depend on the number of trapped atoms. (© 2010 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Density functional computations of 99Ru chemical shifts: relativistic effects, influence of the density functional, and study of solvent effects on fac,[Ru(CO)3I3],MAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2006Jochen Autschbach Abstract Solvent effects on the 99Ru NMR chemical shift of the complex fac,[Ru(CO)3I3], are investigated computationally using density functional theory. Further, benchmark calculations of the 99Ru shift for a set of ten Ru complexes have been performed in order to calibrate the computational model and to determine the importance of relativistic effects on the 99Ru nuclear magnetic shielding and on the chemical shift. A computational model for fac,[Ru(CO)3I3], that includes both explicit solvent molecules and a continuum model is shown to yield the best agreement with experiment. Relativistic corrections are shown to be of minor importance for determining 99Ru chemical shifts. On the other hand, the nature of the density functional is of importance. In agreement with literature data for ligand trends of 99Ru chemical shifts, the chemical shift range for different solvents is also best reproduced by a hybrid functional. Copyright © 2006 John Wiley & Sons, Ltd. [source] Density-functional computation of 53Cr NMR chemical shiftsMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2006Michael Bühl Abstract 53Cr chemical shifts of CrO42,, Cr2O72,, CrO3X,, CrO2X2(X = F, Cl), and Cr(CO)5L (L = CO, PF3, CHNH2, CMeNMe2) are computed, using geometries optimized with the gradient-corrected BP86 density functional, at the gauge-including atomic orbitals (GIAO)-, BPW91-, and B3LYP levels. For this set of compounds, substituent effects on ,(53Cr) are better described with the pure BPW91 functional than with B3LYP, in contrast to most other transition-metal chemical shifts studied so far. For selected cases, 53Cr NMR line widths can be rationalized in terms of electric field gradients (EFGs) computed with the BPW91 functional, but in general other factors such as molecular correlation times appear to be dominating. 53Cr chemical shifts and EFGs are predicted for CrO3, Cr(C6H6)2, Cr(C6H6)CO3, and, with reduced reliability, for Cr2(µ2 -O2CH)4. Copyright © 2006 John Wiley & Sons, Ltd. [source] The g -values and hyperfine coupling of amino acid radicals in proteins: comparison of experimental measurements with ab initio calculations,MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2005Sun Un Abstract Electron paramagnetic resonance (EPR) spectroscopy has been extensively used to identify and characterize protein-based redox active amino acid radicals based on their g -values and hyperfine couplings. To better understand how these parameters depend on the electronic structure and environment of the radical, the theoretical g -values and proton hyperfine tensors of three models corresponding to the tyrosyl, tryptophanyl and glycyl radicals were calculated using Gaussian 03. The g -values were determined using the B3LYP/6,31+G(D,P) combination of density functional and basis set, while the hyperfine tensors were determined using the B3LYP/EPR-III and PBE0/EPR-III combinations. Comparisons are made to measured values. It was found that by appropriately accounting for hydrogen bonds and the dielectric constant of the environment, good agreement could be achieved between the calculated and measured g -values. In all three cases, the g -anisotropy arose from significant spin density on a nitrogen or oxygen atom. The calculated hyperfine tensors for the three radicals did not differ significantly from previous calculations. In the case of the tyrosyl radical, it is shown for the first time that the para -position substituent that is opposite of the CO group can break the symmetry of the phenyl ring, leading to different hyperfine tensors for the two large ortho proton couplings. For the tyrosyl and tryptophanyl models, the calculated hyperfine couplings to hydrogen-bonding protons were in very good agreement with measured values for both the tyrosyl and tryptophanyl models. Copyright © 2005 John Wiley & Sons, Ltd. [source] Compton profile study of tinPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2006B. L. Ahuja Abstract In this paper we report the Compton profile of ,-tin, measured at an intermediate resolution, using 661.65-keV ,-radiation from a 137Cs source. We have also computed the Compton profiles for ,- and ,-tin using the CRYSTAL03 code. The Compton profiles within the framework of linear combination of atomic orbitals (LCAO) using Hartree,Fock (HF), density functional (DF) and pseudopotential-HF schemes embodied in the CRYSTAL03 code have been reported for both phases. Good accordance of the experiment for ,-tin with the corresponding theoretical profiles has been observed for the LCAO-HF and DF schemes. A real-space analysis of the experimental Compton profile shows the metal-like behavior of ,-tin. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] DFT LCAO and plane wave calculations of SrZrO3PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2005R. A. Evarestov Abstract The results of the density functional (DFT) LCAO and plane wave (PW) calculations of the electronic and structural properties of four known SrZrO3 phases (Pm3m, I4/mcm, Cmcm and Pbnm) are presented and discussed. The calculated unit cell energies and relative stability of these phases agree well with the experimental sequence of SrZrO3 phases as the temperature increases. The lattice structure parameters optimized in the PW calculations for all four phases are in good agreement with the experimental neutron diffraction data. The LCAO and PW results for the electronic structure, density of states and chemical bonding in the cubic phase (Pm3m) are discussed in detail and compared with the results of previous PW calculations. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural and Preliminary Explosive Property Characterizations of New 3,4,5-Triamino-1,2,4-triazolium (Guanazinium) SaltsPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 5 2008Chaza Darwich Abstract Two new highly stable energetic salts were synthesized in reasonable yield by using the high nitrogen-content heterocycle 3,4,5-triamino-1,2,4-triazole and resulting in its picrate and azotetrazolate salts. 3,4,5-Triamino-1,2,4-triazolium picrate (1) and bis(3,4,5-triamino-1,2,4-triazolium) 5,5,-azotetrazolate (2) were characterized analytically and spectroscopically. X-ray diffraction studies revealed that protonation takes place on the nitrogen N1 (crystallographically labelled as N2). The sensitivity of the compounds to shock and friction was also determined by standard BAM tests revealing a low sensitivity for both. B3LYP/6,31G(d,,p) density functional (DFT) calculations were carried out to determine the enthalpy of combustion (,cH(1)=,3737.8,kJ mol,1, ,cH(2)=,4577.8,kJ mol,1) and the standard enthalpy of formation (,fH°(1)=,498.3,kJ mol,1, (,fH°(2)=+524.2,kJ mol,1). The detonation pressures (P(1)=189×108,Pa, P(2)=199×108,Pa) and detonation velocities (D(1)=7015,m s,1, D(2)=7683,m s,1) were calculated using the program EXPLO5. [source] Energetics of galactose, and glucose,aromatic amino acid interactions: Implications for binding in galactose-specific proteinsPROTEIN SCIENCE, Issue 9 2004Mannargudi S. Sujatha Abstract An aromatic amino acid is present in the binding site of a number of sugar binding proteins. The interaction of the saccharide with the aromatic residue is determined by their relative position as well as orientation. The position-orientation of the saccharide relative to the aromatic residue was found to vary in different sugar-binding proteins. In the present study, interaction energies of the complexes of galactose (Gal) and of glucose (Glc) with aromatic residue analogs have been calculated by ab initio density functional (U-B3LYP/ 6-31G**) theory. The position-orientations of the saccharide with respect to the aromatic residue observed in various Gal-, Glc-, and mannose,protein complexes were chosen for the interaction energy calculations. The results of these calculations show that galactose can interact with the aromatic residue with similar interaction energies in a number of position-orientations. The interaction energy of Gal,aromatic residue analog complex in position-orientations observed for the bound saccharide in Glc/Man,protein complexes is comparable to the Glc,aromatic residue analog complex in the same position-orientation. In contrast, there is a large variation in interaction energies of complexes of Glc- and of Gal- with the aromatic residue analog in position-orientations observed in Gal,protein complexes. Furthermore, the conformation wherein the O6 atom is away from the aromatic residue is preferred for the exocyclic ,CH2OH group in Gal,aromatic residue analog complexes. The implications of these results for saccharide binding in Gal-specific proteins and the possible role of the aromatic amino acid to ensure proper positioning and orientation of galactose in the binding site have been discussed. [source] Can [M(H)2(H2)(PXP)] Pincer Complexes (M=Fe, Ru, Os; X=N, O, S) Serve as Catalyst Lead Structures for NH3 Synthesis from N2 and H2?CHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2007Markus Hölscher Dr. Abstract The potential of pincer complexes [M(H)2(H2)(PXP)] (M=Fe, Ru, Os; X=N, O, S) to coordinate, activate, and thus catalyze the reaction of N2 with classical or nonclassical hydrogen centers present at the metal center, with the aim of forming NH3 with H2 as the only other reagent, was explored by means of DF (density functional) calculations. Screening of various complexes for their ability to perform initial hydrogen transfer to coordinated N2 showed ruthenium pincer complexes to be more promising than the corresponding iron and osmium analogues. The ligand backbone influences the reaction dramatically: the presence of pyridine and thioether groups as backbones in the ligand result in inactive catalysts, whereas ether groups such as ,-pyran and furan enable the reaction and result in unprecedented low activation barriers (23.7 and 22.1,kcal,mol,1, respectively), low enough to be interesting for practical application. Catalytic cycles were calculated for [Ru(H)2(H2)(POP)] catalysts (POP=2,5-bis(dimethylphosphanylmethyl)furan and 2,6-bis(dimethylphosphanylmethyl)-,-pyran). The height of activation barriers for the furan system is somewhat more advantageous. Formation of inactive metal nitrides has not been observed. SCRF calculations were used to introduce solvent (toluene) effects. The Gibbs free energies of activation of the numerous single reaction steps do not change significantly when solvent is included. The reaction steps associated with the formation of the active catalyst from precursors [M(H)2(H2)(PXP)] were also calculated. The otherwise inactive pyridine ligand system allows for the generation of the active catalyst species, whereas the ether ligand systems show activation barriers that could prohibit practical application. Consequently the generation of the active catalyst species needs to be addressed in further studies. [source] Theoretical Description of Substituent Effects in Electrophilic Aromatic Substitution ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 35 2008Tobias Schwabe Abstract The ability of the current Kohn,Sham density functional theory (DFT) to compute the change of the proton affinity (PA) of phenol derivatives due to substitution is investigated. These systems can be used as models to predict reactivities in electrophilic aromatic substitution reactions. The complexity of the problem is increased systematically by introducing successively up to four substituents in five typical cases (methyl, cyano, fluorine, chlorine, and bromine). Our investigation can be regarded as representative for an important class of problems consistently encountered in the DFT modeling of organic reactions. High-level theoretical reference data from CCSD(T) and SCS-MP2 wave-function calculations are presented, and the PAs are compared to those obtained by a series of density functionals (DFs). It is shown that not all DFs are capable of quantitatively reproducing the substituent effects. These can be simply linear in the number of substituents or show more complicated patterns. Especially for halogens, some DFs even fail completely. In these cases, linearly increasing errors with the number of groups are observed. Reliable results are obtained with hybrid DFs or the even more accurate double-hybrid DF approach. The errors are attributed to the common self-interaction (over-delocalization) error in part of the DFs. Comparison with Hartree,Fock results shows that a reliable account of electron correlation is necessary to compute the PA of unsaturated and highly substituted molecules with chemical accuracy.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Assessing the performances of some recently proposed density functionals for the description of bond dissociations involving organic radicalsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2010Vincent Tognetti Abstract In this article, we have assessed the performances of some recently proposed density functionals for the prediction of reaction energies involving radicals, notably bond dissociations of small organic molecules or of TEMPO-based ones, and ,-scissions, focusing on our TCA family and on range-separated hybrids. It is found that no functional belonging to these two families is able to compete with the M0x one. We have tried to improve the performances of the range-separated hybrids by the optimization of the attenuation parameter, but the improvements for one dataset lead to an unavoidable deterioration for the others. Furthermore, the differences between two different approaches to the long-range/short-range separation are discussed in terms of average enhancement factors, emphasizing the crucial choice of the approximate scheme used for the short-range part. Finally, the influence of the geometries has been considered and found to be negligible for this kind of molecular sets, validating the usual single point energies strategies developed in such benchmarking assessments. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] A DFT study of two diiron (II) synthetic model compounds and their diiron(III) peroxide oxygenation productsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2009R. C. Binning Jr. Abstract Unrestricted density functional theory calculations have been conducted on two diiron(II) synthetic model compounds. Calculations employed the BPW91 and BOP density functionals with both high-spin and broken symmetry low-spin representations of weakly coupled high-spin irons. Comparison of the calculated and crystallographic structures is made, and good agreement is found with both spin representations. Raman spectral data are available for the diiron(III) product of the reaction with O2 to form a bridged peroxide. Calculated harmonic frequencies confirm the experimental assignments. Small geometry differences between the high spin and broken symmetry results are seen in bond lengths, angles, Raman frequencies, and spin densities associated with oxo and peroxo bridges in the diiron(III) oxidation products. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] | ||||||||||||||||||||||||||||