Electron density properties

Book Chattaraj PK (ed) (2009) Chemical reactivity theory. CRC press, Boca Raton, FL. Historical account by Parr, then theoretical development of electron density properties and reactivity indexes. Review of hook Hackett JC (2010) J Am Chem Soc 132 7558... 

Most of the electronic structure calculations have concentrated on (1) the structure, (2) long-range interaction, (3) peptide-water interaction, and (4) electronic properties. These studies have also affirmed the central role played by the H-bonding interactions in protein. The possibility of the AIM theory to analyze a polypeptide or a particular portion of a peptide has been described [6,323,324]. The existence of H-bond in the peptides has been confirmed by the presence of corresponding bond path in the electron density. Properties associated with the path have also been characterized in terms of p r ) at HBCPs and ring CPs. 

It is appropriate to mention here that a generalized picture of H-bonded interaction has emerged from the electron density properties at HBCPs. 

L. F. Pacios and P. C. Gomez, Dependence of calculated NMR proton chemical shifts on electron density properties in proton-transfer processes on short strong hydrogen bonds, J. Phys. Chem. A 108, 11783-11792 (2004). 

Mata I, Alkorta 1, Espinosa E, Molins E (2011) Relationships between interaction energy, intermolecular distance and electron density properties in hydrogen bonded complexes under external electric fields. Chem Phys Lett 507 185... 

Vener MV, Egorova AN, Churakov AV, Tsrrelson VG (2012) Intermolecular hydrogen bond energies in crystals evaluated using electron density properties DFT computations with periodic boundary conditions. J Comput Chem 33 2303... 

N. Otero, M. Mandado and R. A. Mosquera. Nucleophilicity of indole derivatives Activating and deactivating effects based on proton affinities and electron density properties. J. Phys. Chem. A 111, 2007, 5557. 

In DFT, the electronic density rather than the wavefiinction is tire basic variable. Flohenberg and Kohn showed [24] that all the observable ground-state properties of a system of interacting electrons moving in an external potential are uniquely dependent on the charge density p(r) that minimizes the system s total... 

To see how it might make sense that a property such as the kinetic energy, whose operator -h 2m involves derivatives, can be related to the electron density, consider a... 

The energy obtained from a calculation using ECP basis sets is termed valence energy. Also, the virial theorem no longer applies to the calculation. Some molecular properties may no longer be computed accurately if they are dependent on the electron density near the nucleus. 

Many molecular properties can be related directly to the wave function or total electron density. Some examples are dipole moments, polarizability, the electrostatic potential, and charges on atoms. 

Molecular volumes are usually computed by a nonquantum mechanical method, which integrates the area inside a van der Waals or Connolly surface of some sort. Alternatively, molecular volume can be determined by choosing an isosurface of the electron density and determining the volume inside of that surface. Thus, one could find the isosurface that contains a certain percentage of the electron density. These properties are important due to their relationship to certain applications, such as determining whether a molecule will fit in the active site of an enzyme, predicting liquid densities, and determining the cavity size for solvation calculations. 

Once the job is completed, the UniChem GUI can be used to visualize results. It can be used to visualize common three-dimensional properties, such as electron density, orbital densities, electrostatic potentials, and spin density. It supports both the visualization of three-dimensional surfaces and colorized or contoured two-dimensional planes. There is a lot of control over colors, rendering quality, and the like. The final image can be printed or saved in several file formats. 

Crystal can compute a number of properties, such as Mulliken population analysis, electron density, multipoles. X-ray structure factors, electrostatic potential, band structures, Fermi contact densities, hyperfine tensors, DOS, electron momentum distribution, and Compton profiles. 

The macmolplt graphics package is designed for displaying the output of GAMESS calculations. It can display molecular structures, including an animation of reaction-path trajectories. It also may be used to visualize properties, such as the electron density, orbitals, and electrostatic potential in two or three dimensions. 

The orbital and resonance models for bonding in arylamines are simply alternative ways of describing the same phenomenon Delocalization of the nitrogen lone pair decreases the electron density at nitrogen while increasing it m the rr system of the aro matic ring We ve already seen one chemical consequence of this m the high level of reactivity of aniline m electrophilic aromatic substitution reactions (Section 12 12) Other ways m which electron delocalization affects the properties of arylamines are described m later sections of this chapter... 

In addition to total energy and gradient, HyperChem can use quantum mechanical methods to calculate several other properties. The properties include the dipole moment, total electron density, total spin density, electrostatic potential, heats of formation, orbital energy levels, vibrational normal modes and frequencies, infrared spectrum intensities, and ultraviolet-visible spectrum frequencies and intensities. The HyperChem log file includes energy, gradient, and dipole values, while HIN files store atomic charge values. 

The total electron density contributed by all the electrons in any molecule is a property that can be visualized and it is possible to imagine an experiment in which it could be observed. It is when we try to break down this electron density into a contribution from each electron that problems arise. The methods employing hybrid orbitals or equivalent orbitals are useful in certain circumsfances such as in rationalizing properties of a localized part of fhe molecule. Flowever, fhe promotion of an electron from one orbifal fo anofher, in an electronic transition, or the complete removal of it, in an ionization process, both obey symmetry selection mles. For this reason the orbitals used to describe the difference befween eifher fwo electronic states of the molecule or an electronic state of the molecule and an electronic state of the positive ion must be MOs which belong to symmetry species of the point group to which the molecule belongs. Such orbitals are called symmetry orbitals and are the only type we shall consider here. 

The physical properties of amine oxides are attributed to the semipolar or coordinate bond between the oxygen and nitrogen atoms with high electron density residing on oxygen. 

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