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Electron Localization Function (electron + localization_function)

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Chemistry94%

Selected Abstracts

Energetic and topological analysis of the reaction of Mo and Mo2 with NH3, C2H2, and C2H4 molecules

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2004
Maria Del Carmen Michelini
Abstract The Density functional theory has been applied to characterize the structural features of Mo1,2NH3,C2H4, and C2H2 compounds. Coordination modes, geometrical structures, and binding energies have been calculated for several spin multiplets. It has been shown that in contrast to the conserved spin cases (Mo1,2NH3), the interaction between Mo (or Mo2) and C2H4 (or C2H2) are the low-spin (MoC2H4 and C2H2) and high-spin (Mo2C2H4 and C2H2) complexes. In the ground state of Mo1,2C2H4 and C2H2, the metal-center always reacts with the CC center. The spontaneous formation of the global minima is found to be possible due to the crossing between the potential energy surfaces (ground and excited states with respect to the metallic center). The bonding characterization has been performed using the topological analysis of the Electron Localization Function. It has been shown that the most stable electronic structure for a ,-acceptor ligand correlates with a maximum charge transfer from the metal center to the CC bond of the unsaturated hydrocarbons, resulting in the formation of two new basins located on the carbon atoms (away from hydrogen atoms) and the reduction of the number of attractors of the CC basin. The interaction between Mo1,2 and C2H4 (or C2H2) should be considered as a chemical reaction, which causes the multiplicity change. Contrarily, there is no charge transfer between Mo1,2 and NH3, and the partners are bound by an electrostatic interaction. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 1647,1655, 2004 [source]

Electron localization functions obtained from X-ray constrained Hartree,Fock wavefunctions for mol­ecular crystals of ammonia, urea and alloxan,

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2004
Dylan Jayatilaka
Constrained Hartree,Fock wavefunctions in the superposition of isolated molecules model have been calculated from precise X-ray diffraction data on crystals of ammonia (NH3), urea [CO(NH2)2] and alloxan [(CO)4(NH)2]. The X-ray constrained wavefunctions have been used to derive and examine `electron localization' information, quantified by the true and approximate electron localization function (ELF), and the true and approximate Fermi hole mobility function (FHMF). The plots of the Fermi hole mobility function are the first to appear in the literature. The results are compared with corresponding isolated-molecule Hartree,Fock calculations to gauge the effect of the crystal environment on the isolated molecules. An error analysis is performed to indicate the features in the plots which are well determined from the experimental data. The results from all plots are broadly consistent, but the approximate ELF shows some artifacts relative to the true ELF. [source]

Structure and bonding in some S -methylsulfonium halides

HETEROATOM CHEMISTRY, Issue 4 2005
D. B. Chesnut
Density functional theory (DFT) calculations have been carried out at the B3LYP 6-311+G(d,p) level to characterize the geometric and electronic characteristics of a series of S-methylsulfonium halides that possess unusual molecular structures. Atoms-in-molecules (AIM), electron localization function (ELF), and NMR data support the idea that the binding in these gas phase species is predominately ionic with some small degree of covalent bonding. © 2005 Wiley Periodicals, Inc. 16:263,270, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20087 [source]

Transition Metal Borides: Superhard versus Ultra-incompressible,

ADVANCED MATERIALS, Issue 19 2008
Qinfen Gu
Borides of several heavy transition metals have been synthesized by arc melting at ambient pressure. The materials are characterized by either low compressibility or high hardness, some of them showing a good compromise between both properties. The structure,property relationship is revealed based on their crystal structures and a chemical bonding analysis by means of the electron localization function. [source]

Competitive coordination between lead and oligoelements with respect to some therapeutic heavy-metal chelators

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2008
C. Gourlaouen
Abstract The competitive complexation of Ca2+, Fe2+, Cu2+, Zn2+, and Pb2+ toward ethylene diamine tetraacetate (EDTA), dimercaprol and D -penicillamine, three liganding agents commonly used in chelation therapy against heavy metal, especially lead, poisonings is examined by means of B3LYP calculations, natural population analyses, and the topological analysis of the electron localization function. It is shown that Pb2+ can displace any of Ca2+, Fe2+, Cu2+, or Zn2+ chelated by any of dimercaprol or D -penicillamine, but can only displace Ca2+ if EDTA is concerned. The first two chelators thus appear as better entities than EDTA to be used in chelation therapy, where in vivo selective complexation is essential. Moreover, the comparison of the bonding characteristics of Pb2+ with those of the other cations allows deriving three features to be taken into account in designing new chelators expecting to have an increased selectivity toward this cation. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

WinXPRO: a program for calculating crystal and molecular properties using multipole parameters of the electron density

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2002
Adam Stash
The computer program WinXPRO enables the calculation of crystal and molecular properties using the multipole parameters of the electron density. The list of properties includes the electron density and its topological and electric field characteristics, the local kinetic and potential energies, the electron localization function, and the effective crystal potential. WinXPRO works under the Windows operating system and can utilize any existing graphics program to display output. [source]

Advancing beyond charge analysis using the electronic localization function: Chemically intuitive distribution of electrostatic moments

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2008
Julien Pilmé
Abstract We propose here an evaluation of chemically intuitive distributed electrostatic moments using the topological analysis of the electron localization function (ELF). As this partition of the total charge density provides an accurate representation of the molecular dipole, the distributed electrostatic moments based on the ELF partition (DEMEP) allows computing of local moments located at non atomic centers such as lone pairs, , bonds and , systems. As the local dipole contribution can be decomposed in polarization and charge transfer components, our results indicate that local dipolar polarization of the lone pairs and chemical reactivity are closely related whereas the charge transfer contribution is the key factor driving the local bond dipole. Results on relevant molecules show that local dipole contributions can be used to rationalize inductive polarization effects in alcohols derivatives and typical hydrogen bond interactions. Moreover, bond quadrupole polarization moments being related to a , character enable to discuss bond multiplicities, and to sort families of molecules according to their bond order. That way, the nature of the CO bond has been revisited for several typical systems by means of the DEMEP analysis which appears also helpful to discuss aromaticity. Special attention has been given to the carbon monoxide molecule, to the CuCO complex and to a weak intramolecular N|---CO interaction involved in several biological systems. In this latter case, it is confirmed that the bond formation is mainly linked to the CO bond polarization. Transferability tests show that the approach is suitable for the design of advanced force fields. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008 [source]

New insights on the bridge carbon,carbon bond in propellanes: A theoretical study based on the analysis of the electron localization function

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 5 2007
Victor Polo
Abstract The nature of the bonding between bridgehead carbon atoms (Ca, Ca,) as well as the ring strain in a family of 10 propellanes formed by three-, four-, or five-member rings: [1.1.1] (I), [2.1.1] (II), [3.1.1] (III), [2.2.1] (IV), [3.2.1] (V), [2.2.2] (VI), [3.3.1] (VII), [3.2.2] (VIII), [3.3.2] (IX), and [3.3.3] (X) are studied by means of the electron localization function (ELF) at the DFT level (B3LYP/cc-pVTZ). The ELF analysis of smaller propellanes (I, II, and III) reveals the coexistence of two resonance forms: one with a nonbonding electron pair partially delocalized between Ca and Ca, atoms outside the cage (ionic) and the other with a bridge bond between the same atoms (covalent). The weights of each form are calculated according to the ELF-basin populations, yielding 94, 88, and 53% for the ionic structure of I, II, and III, respectively, while larger propellanes (IV,X) present only the covalent form. The question of the s-character of the bridge bond is addressed by dissecting the bridge-bond ELF basin into the molecular orbital contributions. Finally, ,-aromaticity associated to surface electron delocalization has been analyzed by means of nucleus-independent chemical shift (NICS) calculations. The results point out that the stability of the fused ring structure of propellanes I, II, and III, can be assigned to the remarkable ,-aromaticity of the involved three-member rings. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source]

Electron pairing and chemical bonds: Pair localization in ELF domains from the analysis of domain averaged Fermi holes

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2007
Robert Ponec
Abstract This article reports the application of a recently proposed formalism of domain averaged Fermi holes to the problem of the localization of electron pairs in electron localization function (ELF) domains and its possible implications for the electron pair model of chemical bond. The main focus was on the systems, such as H2O or N2, in which the "unphysical" population of ELF domains makes the parallel between these domains and chemical bond questionable. On the basis of the results of the Fermi-hole analysis, we propose that the above problems could be due to the fact that in some cases the boundaries of the ELF domains need not be determined precisely enough. © 2006 Wiley Periodicals, Inc. J Comput Chem, 2006 [source]

A joint study based on the electron localization function and catastrophe theory of the chameleonic and centauric models for the Cope rearrangement of 1,5-hexadiene and its cyano derivatives

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2005
Victor Polo
Abstract A novel interpretation of the chameleonic and centauric models for the Cope rearrangements of 1,5-hexadiene (A) and different cyano derivatives (B: 2,5-dicyano, C: 1,3,4,6-tetracyano, and D: 1,3,5-tricyano) is presented by using the topological analysis of the electron localization function (ELF) and Thom's catastrophe theory (CT) on the reaction paths calculated at the B3LYP/6-31G(d,p) level. The progress of the reaction is monitorized by the changes of the ELF structural stability domains (SSD), each being change controlled by a turning point derived from CT. The reaction mechanism of the parent reaction A is characterized by nine ELF SSDs. All processes occur in the vicinity of the transition structure and corresponding to a concerted formation/breaking of C1C6 and C3C4 bonds, respectively, together with an accumulation of charge density onto C2 and C5 atoms. Reaction B presents the same number of ELF SSDs as A, but a different order appears; the presence of 2,5-dicyano substituents favors the formation of C1C6 bonds over the breaking of C3C4 bond process, changing the reaction mechanism from a concerted towards a stepwise, via a cyclohexane biradical intermediate. On the other side, reaction C presents the same type of turning points but two ELF SSD less than A or B; there is an enhancement of the C3C4 bond breaking process at an earlier stage of the reaction by delocalizing the electrons from the C3C4 bond among the cyano groups. In the case of competitive effects of cyano subsituents on each moiety, as it is for reaction D, seven different ELF SSDs have been identified separated by eight turning points (two of them occur simultaneously). Both processes, formation/breaking of C1C6 and C3C4 bonds, are slightly favored with respect to the parent reaction (A), and the TS presents mixed electronic features of both B and C. The employed methodology provides theoretical support for the centauric nature (half-allyl, half-radical) for the TS of D. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1427,1437, 2005 [source]

Electron pairing and chemical bonds.

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2005
Electron fluctuation, pair localization in ELF domains
Abstract This article reports the numerical comparison of the quantities characterizing the extent of electron fluctuation and pair localization in the domains determined by the direct minimization of electron fluctuation with the domains resulting from the partitioning of the molecules based on the topological analysis of the so-called electron localization function (ELF). Such a comparison demonstrates that the ELF partitioning can be regarded as a feasible alternative to computationally much more demanding direct optimization of minimum fluctuation domains. This opened the possibility of the systematic scrutiny of the electron pair model of the chemical bond, and as it was demonstrated, the previous pessimistic claims about the applicability of this model are not completely justified. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1205,1213, 2005 [source]

Wave functions derived from experiment.

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2003

Abstract The constrained Hartree,Fock method using experimental X-ray diffraction data is extended and applied to the case of noncentrosymmetric molecular crystals. A new way to estimate the errors in derived properties as a derivative with respect to added Gaussian noise is also described. Three molecular crystals are examined: ammonia [NH3], urea [CO(NH2)2], and alloxan [(CO)4(NH)2]. The energetic and electrical properties of these molecules in the crystalline state are presented. In all cases, an enhancement of the dipole moment is observed upon application of the experimental constraint. It is found that the phases of the structure factors are robustly determined by the constrained Hartree,Fock model, even in the presence of simulated noise. Plots of the electron density, electrostatic potential, and the electron localization function for the molecules in the crystal are displayed. In general, relative to the Hartree,Fock model, there is a depletion of charge around hydrogen atoms and lone pair regions, and a build-up of charge within the molecular framework near nuclei, directed along the bonds. The electron localization function plots reveal an increase in the pair density between vicinal hydrogen atoms. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 470,483, 2003 [source]

Electron localization functions obtained from X-ray constrained Hartree,Fock wavefunctions for mol­ecular crystals of ammonia, urea and alloxan,

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2004
Dylan Jayatilaka
Constrained Hartree,Fock wavefunctions in the superposition of isolated molecules model have been calculated from precise X-ray diffraction data on crystals of ammonia (NH3), urea [CO(NH2)2] and alloxan [(CO)4(NH)2]. The X-ray constrained wavefunctions have been used to derive and examine `electron localization' information, quantified by the true and approximate electron localization function (ELF), and the true and approximate Fermi hole mobility function (FHMF). The plots of the Fermi hole mobility function are the first to appear in the literature. The results are compared with corresponding isolated-molecule Hartree,Fock calculations to gauge the effect of the crystal environment on the isolated molecules. An error analysis is performed to indicate the features in the plots which are well determined from the experimental data. The results from all plots are broadly consistent, but the approximate ELF shows some artifacts relative to the true ELF. [source]

Electron Fluctuation in Pericyclic and Pseudopericyclic Reactions

CHEMPHYSCHEM, Issue 1 2006
Eduard Matito
Borderline cases: Differentiating between pericyclic and pseudopericyclic reactions is controversial. The authors analyze the electron distribution of the transition state of some known and some controversial reactions by means of the electron localization function (ELF) to elucidate their mechanism (see figure). This analysis provides a definitive criterion to distinguish between both electrocyclic processes. [source]

Disproving a Silicon Analog of an Alkyne with the Aid of Topological Analyses of the Electronic Structure and Ab Initio Molecular Dynamics Calculations

CHEMPHYSCHEM, Issue 9 2005
Carlo A. Pignedoli Dr.
Abstract A silicon compound has recently been synthesized that was claimed to exhibit the first realization of a silicon,silicon triple bond. We debate this classification on the basis of a thorough investigation of the nature of the chemical bond, using the rigorous topological analysis of the electron density as developed in Bader's atoms-in-molecules theory, that of the electron localization function and the related orbital-independent definitions of the bond order. Our results refer both to the ground-state geometry and to nonequilibrium configurations, which are accessed by the system in a room-temperature ab initio molecular dynamics simulation. We also use the reciprocal compliance force constant as an independent chemical descriptor. All the above procedures are in agreement and do not support the classification of the silicon,silicon central bond as triple. The characterization which consistently emerges from the present study is one in which two electron pairs participate in the bonding and the other pair belongs mainly to nonbonding regions. [source]