Ab initio calculations of electrostatic potentials and deformation densities for a series of choline ester model systems

1980 ◽  
Vol 55 (4) ◽  
pp. 267-281 ◽  
Author(s):  
Helge Johansen ◽  
Sten Rettrup ◽  
Birthe Jensen
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Electrostatic Potentials ◽  
Model Systems ◽  
Choline Ester

Interaction between copper(II) ions through the azido bridge: concept of spin polarization and ab initio calculations on model systems

1986 ◽  
Vol 108 (10) ◽  
pp. 2574-2581 ◽  
Author(s):  
Marie France. Charlot ◽  
Olivier. Kahn ◽  
Max. Chaillet ◽  
Christiane. Larrieu
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Spin Polarization ◽  
Model Systems

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.

scholarly journals Bonding in 1,2,3-Triazoles. VII. Effects of N-Substitution. Ab Initio Calculations on Model Systems.

1993 ◽  
Vol 47 ◽  
pp. 943-949 ◽  
Author(s):  
Kurt Nielsen ◽  
Inger Søtofte ◽  
Helge Johansen ◽  
Erwan Le Clouerec ◽  
Jaume Casabó ◽  
...  
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Model Systems

Millimetre-wave and infrared spectroscopy of Br13 CN: anharmonic force field of cyanogen bromide from spectroscopic data and ab initio calculations

1997 ◽  
Vol 90 (3) ◽  
pp. 495-497
Author(s):  
CLAUDIO ESPOSTI ◽  
FILIPPO TAMASSIA ◽  
CRISTINA PUZZARINI ◽  
RICCARDO TARRONI ◽  
ZDENEK ZELINGER
Keyword(s):  
Infrared Spectroscopy ◽  
Force Field ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Spectroscopic Data ◽  
Cyanogen Bromide ◽  
Millimetre Wave ◽  
Anharmonic Force
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