The nature of the chemical bond in sodium tungstate based on ab initio, DFT and QTAIM topological analysis of electron density

2021 ◽  
Author(s):  
G.N. Anil Kumar ◽  
D.L. Shruthi
Keyword(s):  
Ab Initio ◽  
Electron Density ◽  
Chemical Bond ◽  
Sodium Tungstate ◽  
Topological Analysis ◽  
Ab Initio Dft

Analysis of magnesium–carbon bonding in magnesium anthracene systems

1996 ◽  
Vol 74 (6) ◽  
pp. 801-809 ◽  
Author(s):  
Ralf Stegmann ◽  
Gernot Frenking
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Electron Density ◽  
Chemical Shifts ◽  
Topological Analysis ◽  
Nbo Analysis ◽  
Experimental Values ◽  
A Charge ◽  
Good Agreement ◽  
Carbon Bonding

Ab initio calculations at the MP2/3-21G(*) level of theory have been carried out for the magnesium–anthracene complexes 9,10-magnesiumanthracene•3H2O (1) and the 9-methyl (2), dimethyl (3), and 9,10-bis(methylsilyl) (4) substituted derivatives. The theoretically predicted geometries of the anthracene ligands are also reported. The calculated geometries of 1–4 are in very good agreement with experimental values for the corresponding THF complexes. The Mg—C9,10 bonds of the bridged structures are rather long and the anthracene ligands are folded by ~40° along the C9–C10 line in the complexes. Analysis of the electronic structure shows clearly that the Mg—C9,10 bonds should be considered as purely ionic. This is revealed by topological analysis of the electron density distribution and its associated Laplacian. The electron density at the Mg—C9,10 bond critical points ρ(rb) is very low and the Laplacian [Formula: see text] and the energy density Hb have positive values. The ionic nature of the Mg—C9,10 bond is also indicated by the natural bond order (NBO) analysis, which gives a Lewis structure with two lone pairs at C9 and C10 but no Mg—C9,10 bonds. The NBO method gives a charge donation from Mg to the anthracene ligand of nearly two. The theoretically predicted NMR chemical shifts using the GIAO method give 13C resonances for the complex 1 and for anthracene and anthracene dianion that are in good agreement with experimental values. Key words: magnesium–anthracene complexes, ab initio calculations, analysis of magnesium–carbon bonding.

Peptide models XXVII. An exploratory ab initio study on the 21st amino acid side-chain conformations of N-formyl-L-selenocysteinamide (For-L-Sec-NH2) and N-acetyl-L-selenocysteine-N-methylamide (Ac-L-Sec-NHMe) in their γL backbone conformation

2000 ◽  
Vol 78 (3) ◽  
pp. 395-408 ◽  
Author(s):  
Judith C Vank ◽  
Carlos P Sosa ◽  
Andras Perczel ◽  
Imre G Csizmadia
Keyword(s):  
Ab Initio ◽  
Electron Density ◽  
Single Point ◽  
Topological Analysis ◽  
Side Chain ◽  
Amino Acid Side Chain ◽  
Backbone Conformation ◽  
Density Analysis ◽  
Peptide Models ◽  
Chain Conformations

Selenocysteine is expected to have 9 × 9 = 81 conformations [3 × 3 = 9 backbone: ψ (g+,a,g-) × ϕ (g+,a,g-) and 3 × 3 = 9 side-chain: χ1 (g+,a,g-) × χ2 (g+,a,g-)]. In the present study, all the torsional modes of the side-chain (χ1: rotation about the Cα-Cβ and χ2: rotation about the Cβ-Se bonds) were investigated in the relaxed γL backbone [(ϕ,ψ); (g-,g+)] conformation. Seven out of the nine expected minima were found at the RHF/3-21G level of theory for N-formyl-L-selenocysteinamide (For-L-Sec-NH2) and N-acetyl-L-selenocysteine-N-methylamide (Ac-L-Sec-NHMe). The stabilization energy exerted by the -CH2-SeH side-chain has been compared with that of -CH2-SH and -CH2-OH. Relative energies of the various conformers were also obtained via single point calculations at the B3LYP/6-31G(d,p) level of theory. Topological analysis of the electron density has been performed by Bader's Atoms in Molecule (AIM) approach using the results. The structures were also optimized at the B3LYP/6-31+G(d,p) level of theory.Key words: selenocysteine side-chain conformations, ab initio MO study, Multidimensional Conformational Analysis (MDCA), Atoms in Molecules (AIM), Bader's electron density analysis.

Comparison of pnicogen and tetrel bonds in complexes containing CX2 carbenes (X = F, Cl, Br, OH, OMe, NH2, and NMe2)

2019 ◽  
Vol 43 (39) ◽  
pp. 15596-15604 ◽  
Author(s):  
Hui Lin ◽  
Lingpeng Meng ◽  
Xiaoyan Li ◽  
Yanli Zeng ◽  
Xueying Zhang
Keyword(s):  
Ab Initio ◽  
Electron Density ◽  
Topological Analysis ◽  
Similarities And Differences ◽  
Tetrel Bonds

The similarities and differences of pnicogen and tetrel bonds formed by carbenes CX2 with H3AsO and H3SiCN were investigated by carrying out ab initio calculations in association with topological analysis of electron density.

Benzooxirene, naphthooxirenes, and anthraceneoxirenes: the stabilization of the oxirene system by bond fixation in acenes. A comparison of ab initio and DFT in the investigation of annelated oxirenes

2000 ◽  
Vol 78 (2) ◽  
pp. 297-306 ◽  
Author(s):  
E Lewars
Keyword(s):  
Ab Initio ◽  
Electron Density ◽  
Ring Opening ◽  
Bond Order ◽  
Linear Series ◽  
Bond Orders ◽  
Resonance Structures ◽  
Ca 50 ◽  
Ab Initio And Dft ◽  
Ab Initio Dft

The effect on the stabilities of benzoannelated oxirenes (oxacyclopropenes) of variations in the C-C bond electron density (as measured by Löwdin bond order) was studied computationally. Benzo[b]oxirene (4ox), naphtho[2,3-b]oxirene (5ox), naphtho[1,2-b]oxirene (6ox), anthro[2,3-b]oxirene (7ox), and anthro[1,2-b]oxirene (8ox) were investigated using the DFT pBP/DN* method as implemented in the program Spartan. This method was chosen because with 4ox it gave results similar to those from the much slower QCISD(T)/6-31G*//MP2(full)/6-31G* and MP4SDTQ/6-31G*//MP2(full)/6-31G* methods. The calculated barriers to oxirene ring opening for the "linear" 4ox, 5ox, and 7ox (bond orders 1.35, 1.24, and 1.20, respectively) were 23.6, 39.9, and 46.6 kJ mol-1, in contrast to the "angular" 6ox and 8ox (bond orders 1.50 and 1.59, respectively), with barriers of ca. 0 kJ mol-1. The high-barrier vs. low-barrier series corresponds to the stabilities expected from the resonance structures of the oxirenes or their formal precursor acenes. Empirically, the ring-opening barriers were linearly related to the oxirene bond orders, and extrapolation to tetracene using this relationship gave a barrier of ca. 50 kJ mol-1, which seems to be the limiting barrier in the linear series. In several cases the oxirene isomerized to a ketene without going through an oxo carbene (ketocarbene). Benzoannelation is only the second kind of substitution (after dimethyl substitution) that has been indicated, computationally, to be able to stabilize oxirenes.Key words: oxirenes, ketocarbenes, benzooxirenes, AM1, ab initio, DFT.

Revisiting the charge density analysis of 2,5-dichloro-1,4-benzoquinone at 20 K

2017 ◽  
Vol 73 (4) ◽  
pp. 654-659 ◽  
Author(s):  
Zhijie Chua ◽  
Bartosz Zarychta ◽  
Christopher G. Gianopoulos ◽  
Vladimir V. Zhurov ◽  
A. Alan Pinkerton
Keyword(s):  
Charge Density ◽  
Electron Density ◽  
Topological Analysis ◽  
Diffraction Measurement ◽  
X Ray Diffraction ◽  
Total Electron Density ◽  
Total Electron ◽  
Structure Factors ◽  
Density Analysis ◽  
Experimental Charge Density

A high-resolution X-ray diffraction measurement of 2,5-dichloro-1,4-benzoquinone (DCBQ) at 20 K was carried out. The experimental charge density was modeled using the Hansen–Coppens multipolar expansion and the topology of the electron density was analyzed in terms of the quantum theory of atoms in molecules (QTAIM). Two different multipole models, predominantly differentiated by the treatment of the chlorine atom, were obtained. The experimental results have been compared to theoretical results in the form of a multipolar refinement against theoretical structure factors and through direct topological analysis of the electron density obtained from the optimized periodic wavefunction. The similarity of the properties of the total electron density in all cases demonstrates the robustness of the Hansen–Coppens formalism. All intra- and intermolecular interactions have been characterized.

scholarly journals Topology of the Electron Density and of Its Laplacian from Periodic LCAO Calculations on f-Electron Materials: The Case of Cesium Uranyl Chloride

Molecules ◽  
2021 ◽  
Vol 26 (14) ◽  
pp. 4227
Author(s):  
Alessandro Cossard ◽  
Silvia Casassa ◽  
Carlo Gatti ◽  
Jacques K. Desmarais ◽  
Alessandro Erba
Keyword(s):  
Electron Density ◽  
Chemical Bonding ◽  
Topological Analysis ◽  
Theoretical Description ◽  
Basis Functions ◽  
Quantum Mechanical ◽  
X Ray Diffraction ◽  
X Ray ◽  
Atomic Orbitals ◽  
Uranyl Chloride

The chemistry of f-electrons in lanthanide and actinide materials is yet to be fully rationalized. Quantum-mechanical simulations can provide useful complementary insight to that obtained from experiments. The quantum theory of atoms in molecules and crystals (QTAIMAC), through thorough topological analysis of the electron density (often complemented by that of its Laplacian) constitutes a general and robust theoretical framework to analyze chemical bonding features from a computed wave function. Here, we present the extension of the Topond module (previously limited to work in terms of s-, p- and d-type basis functions only) of the Crystal program to f- and g-type basis functions within the linear combination of atomic orbitals (LCAO) approach. This allows for an effective QTAIMAC analysis of chemical bonding of lanthanide and actinide materials. The new implemented algorithms are applied to the analysis of the spatial distribution of the electron density and its Laplacian of the cesium uranyl chloride, Cs2UO2Cl4, crystal. Discrepancies between the present theoretical description of chemical bonding and that obtained from a previously reconstructed electron density by experimental X-ray diffraction are illustrated and discussed.

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