Basis-Set dependence of exterior electron distributions of molecular orbitals

1986 ◽  
Vol 29 (4) ◽  
pp. 677-688 ◽  
Author(s):  
Koichi Ohno ◽  
Toshimasa Ishida
Keyword(s):  
Molecular Orbitals ◽  
Basis Set ◽  
Electron Distributions

Ab Initio SCF Procedure with Localized Molecular Orbitals of Fragments

1975 ◽  
Vol 30 (11) ◽  
pp. 1499
Author(s):  
J. Koller ◽  
A. Ažman
Keyword(s):  
Ab Initio ◽  
Molecular Orbitals ◽  
Basis Set ◽  
Localized Orbitals ◽  
Localized Molecular Orbitals ◽  
Molecular Systems

An ab initio procedure is described with a basis set of localized orbitals of the fragments. The method was tested on three molecular systems. The results are in agreement with the results of LCAO calculations

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.

Molecular orbital calculations on dinitrogen trioxide, N2O3

1977 ◽  
Vol 30 (12) ◽  
pp. 2613 ◽  
Author(s):  
IJ Doonan ◽  
RGAR Maclagan
Keyword(s):  
Molecular Orbital ◽  
Excited States ◽  
Molecular Orbital Calculation ◽  
Molecular Orbitals ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Localized Molecular Orbitals ◽  
Expansion Technique ◽  
Doubly Excited ◽  
Slater Basis

A minimal Slater basis set molecular orbital calculation on dinitrogen trioxide, N2O3, is reported. In the evaluation of integrals, non-NDDO integrals were calculated by the 3G/s expansion technique. Analysis of the wave function obtained shows weak bonding between the nitrosyl and nitro fragments and a very weak attractive interaction between the cis- oxygens. The molecular orbitals for N2O3 were expanded in terms of the NO and NO2 molecular orbitals. A correlation diagram linking the N2O3 orbitals with the NO and NO2 orbitals is presented. The localized molecular orbitals for N2O3 are analysed. A configuration interaction calculation involving the ground state and nine doubly excited state configurations is reported. Two excited states have significant contributions. A comparison is made between the results obtained by using a 3G/S expansion and a calculation using a 2G/S expansion.

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