Observations of Local Electron Distributions in Molecular Orbitals

1984 ◽  
pp. 761-770 ◽  
Author(s):  
Koichi Ohno ◽  
Yoshiya Harada
Keyword(s):  
Molecular Orbitals ◽  
Local Electron ◽  
Electron Distributions

scholarly journals Unconstrained and X-ray constrained extremely localized molecular orbitals: analysis of the reconstructed electron density

2014 ◽  
Vol 70 (6) ◽  
pp. 532-551 ◽  
Author(s):  
Leonardo H. R. Dos Santos ◽  
Alessandro Genoni ◽  
Piero Macchi
Keyword(s):  
Dipole Moments ◽  
Topological Analysis ◽  
Molecular Orbitals ◽  
Basis Sets ◽  
Electron Densities ◽  
X Ray ◽  
Localized Molecular Orbitals ◽  
New Strategy ◽  
Electron Distributions ◽  
Detailed Assessment

The recently developed X-ray constrained extremely localized molecular orbital (XC-ELMO) technique is a potentially useful tool for the determination and analysis of experimental electron densities. Molecular orbitals strictly localized on atoms, bonds or functional groups allow one to combine the quantum-mechanical rigour of the wavefunction-based approaches with the easy chemical interpretability typical of the traditional multipole models. In this paper, using very high quality X-ray diffraction data for the glycylglycine crystal, a detailed assessment of the capabilities and limitations of this new method is given. In particular, the effects of constraining the ELMO wavefunctions to experimental X-ray structure-factor amplitudes and the ability of the method to reproduce benchmark electron distributions have been accurately investigated. Topological analysis of the XC-ELMO electron densities and of the zero-flux surface-integrated charges and dipole moments shows that the new strategy is already reliable, provided that sufficiently flexible basis sets are used. These analyses also raise new questions and call for further improvements of the method.

EQUIVALENT ORBITALS AND THE SHAPES OF EXCITED SPECIES

1958 ◽  
Vol 36 (1) ◽  
pp. 24-30 ◽  
Author(s):  
J. W. Linnett
Keyword(s):  
Excited State ◽  
Ground States ◽  
Molecular Orbitals ◽  
Considerable Degree ◽  
Excited Species ◽  
Electron Distributions

The electron distributions in the ground states of C2H2, HCO, and NH2, and in one excited state of each species, have been considered by transforming the simple molecular orbitals into equivalent ones. In the light of these considerations, the shapes and dimensions of the above species in these states have been discussed. It is found that a considerable degree of understanding can be achieved though there is uncertainty in the interpretation in some cases.

scholarly journals Extracting Extremely Localized Molecular Orbitals from X-ray Diffraction Data

2014 ◽  
Vol 70 (a1) ◽  
pp. C284-C284 ◽  
Author(s):  
Alessandro Genoni
Keyword(s):  
Wave Function ◽  
Diffraction Data ◽  
Accurate Determination ◽  
Molecular Orbitals ◽  
X Ray Diffraction ◽  
Electron Densities ◽  
X Ray ◽  
Localized Molecular Orbitals ◽  
Electron Distributions

The accurate determination of electron densities in crystals from high-resolution X-ray diffraction data has become more and more important over the years. The existing techniques to accomplish this task can be subdivided into two great families: the multipole models and the wave function-based strategies. The former, which are the most widely used, are essentially linear scaling and allow an easy chemical interpretation of the obtained molecular charge densities, but they are also characterized by some drawbacks, such as the possible presence of unphysical negative regions in the resulting electron distributions. On the contrary, the latter always provide quantum mechanically rigorous electron densities, but they are more computationally expensive and, above all, the ease of chemical interpretation is almost completely lost. In this context, in order to combine the easy chemical interpretability of the multipole models with the quantum mechanical rigor of the wave-function based methods, we have recently extended the X-ray constrained wave function approach proposed by Jayatilaka in the framework of a quantum chemistry technique for the a priori determination of Extremely Localized Molecular Orbitals (ELMOs), namely we have developed a new strategy that allows to extract from X-ray diffraction data a single Slater determinant built up wit Molecular Orbitals strictly localized on small molecular fragments (e.g., atoms, bonds or functional groups). Preliminary tests have shown that the determination of X-ray constrained ELMOs is really straightforward. Furthermore, given the reliable transferability of the obtained Molecular Orbitals, we are constructing new ELMOs databases that can be used as alternative to the existing pseudo-atoms libraries for refining crystallographic structures and electron distributions of large systems. A detailed comparison between the new technique and the multipole models is also currently under investigation.

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