Ab initio calculations of the electron density in the molecules of substituted 1-(4-fluorophenyl)-3-phenyltriazenes

1998 ◽  
Vol 47 (9) ◽  
pp. 1835-1836
Author(s):  
O. V. Shcherbakova ◽  
D. N. Kravtsov ◽  
A. S. Peregudov ◽  
Yu. A. Borisov
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Electron Density ◽  
Substituted 1

Experimental electron density study of 1,2,4-triazole at 15 K. A comparison with ab initio-calculations

1997 ◽  
Vol 212 (3) ◽  
Author(s):  
P. Fuhrmann ◽  
T. Koritsánszky ◽  
P. Luger
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Electron Density ◽  
Diffraction Data ◽  
Topological Properties ◽  
X Ray Diffraction ◽  
X Ray ◽  
Experimental Electron Density ◽  
Density Study

AbstractTopological properties and the Laplacian function of the electron density of 1,2,4-triazole have been determined from X-ray diffraction data collected at 15 K. 1,2,4-Triazole, C

H2O–CH4and H2S–CH4complexes: a direct comparison through molecular beam experiments and ab initio calculations

2015 ◽  
Vol 17 (45) ◽  
pp. 30613-30623 ◽  
Author(s):  
David Cappelletti ◽  
Alessio Bartocci ◽  
Federica Frati ◽  
Luiz F. Roncaratti ◽  
Leonardo Belpassi ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Electron Density ◽  
Molecular Beam ◽  
Electron Density Redistribution ◽  
Transfer Effects

Electron density redistribution upon the formation of the water–methane complex arises from polarisation and charge transfer effects.

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.

scholarly journals A lattice-dynamical refinement approach based on periodic ab-initio calculations

2014 ◽  
Vol 70 (a1) ◽  
pp. C1441-C1441
Author(s):  
Anders Madsen
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Electron Density ◽  
High Performance ◽  
Normal Modes ◽  
Thermal Motion ◽  
Model Systems ◽  
Model Parameters ◽  
Large Area ◽  
X Ray

The use of synchrotron radiation and large area detectors has increased the quality and quantity of X-ray and neutron diffraction data within the last decades. These advances call for new and better approaches to model and to interpret the data. Elastic X-ray diffraction corresponds to the Fourier transform of the thermally averaged electron density in the unit cell. This density is normally approximated as the convolution of a sum of static atomic densities and the thermal motion of the individual atoms. The static densities and thermal motion are equally important: Together they conform the entire model refined against a single set of measured data, and they must both be modeled correctly, or neither is. The advent of high-performance computers has made it feasible to obtain lattice-dynamical models based on periodic quantum-mechanical calculations, to describe the concerted motion of atoms and molecules through the crystal. Our recent calculations of Debye-Waller factors based on periodic ab-initio calculations for various molecular test systems [1] has prepared the ground for proposing the refinement of quantum-mechanically derived normal modes of vibration against diffraction experiments. As opposed to the standard approach using independent atomic motion, some of the advantages and possibilities that emerge are: 1. A physically reasonable picture of the molecular motion in the crystal. 2. Refinement against data obtained at multiple temperatures in a common model. 3. Modeling thermal diffuse scattering. 4. Reduction of the number of model parameters. 5. Anisotropic motion of H atoms. The approach is computationally expensive, but may prove useful for electron density studies, studies of thermal effects in crystals, i.e. studies of thermochromic and thermoelectric compounds, solid-state phase-transitions and to derive thermodynamic properties, e.g. free energies of polymorphic crystals. We will introduce the method and present some first results for model systems.

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