Electronic properties of molecules

Simulation of molecules can be done at the quantum mechanical level, as is necessaiy to determine the electronic properties of molecules, to analyze covalent bonds or simulate bond formation and breaking. However, quantum mechanical simulation is extremely computationally intensive and is too time-consuming for all but the smallest molecular systems. 

Light absorption, by markedly affecting the electronic properties of molecules and metal complexes, may induce intra- or intermolecular electron transfer processes leading to electron-hole separation. 

M. Cossi, N. Rega, G. Scalmani and V. Barone, Energies, structures, and electronic properties of molecules in solution with the C-PCM solvation model, J. Comput. Chem., 24 (2003) 669. 

One of the major advantages of NMR over other structural techniques such as x-ray crystallography is that it has the potential to provide information not only on structure but also on the electronic properties of molecules. Many potential drug leads contain ionizable groups and a determination of their charge state in solution and/or at the bound site or, if relevant, their tautomeric form, can be important in the design of analogues. 

All thermodynamic and electronic properties of molecules are closely linked to the quantum potential. Many of these, for instance electronegativity, only known from empirical relationships before, can now be demonstrated to be of fundamental theoretical importance. The close similarity between chemical potential of a system and the quantum potential of component molecules establishes a direct link between quantum mechanics and thermodynamics, without statistical considerations. This relationship has direct bearing on the nature, mechanism and kinetics of chemical bond formation, including sterically improbable intramolecular rearrangements. 

A molecular descriptor defined in analogy with the Dosmorov complexity index, also accounting for electronic properties of molecules [Bonchev, 1983] ... 

The MOPAC (molecular orbital package), which has been explored by Dr. James J.P. Stewart, is the method by which the electron characteristics of a molecule is calculated. The MOPAC determines both an optimum geometry and the electron properties of molecule by solving the Schrodinger equation, using the MINDO/3 [6], MNDO [7], or AMI [8] semi-empirical Hamiltonians developed by M.J.S. Dewar, the MIND-d Hamiltonian developed by W. Thiel, or the PM3 [9] or PM5 semi-empirical Hamiltonians developed by J.J.P. Stewart. 

Qm QM RECON Mean absolute atomic charge Quantum mechanics An algorithm for the rapid reconstruction of molecular charge densities and charge density-based electronic properties of molecules, using atomic charge density fragments precomputed from ab initio wave functions. The method is based on Bader s quantum theory of atoms in molecules. 

UV/Vis Spectroscopy uses ultraviolet and/or visible light to examine the electronic properties of molecules. Irradiating a molecule with UV or Visible light of a specific wavelenth can cause the electrons in a molecule to transition to an excited state. This technique is most useful for analyzing molecules with conjugated systems or carbonyl bonds. 

Electronic information is combined with shape and steric information to characterize molecules in charged partial surface area descriptors. Other approaches, different from those closely related to quantum-chemistry, refer to electronic distribution in molecules, such as electronic substituent constants, ehctrotopohgical state indices, topological charge indices. Reactivity indices and delocalization degree indices are also related to electronic properties of molecules. 

The original ab initio approach to calculating electronic properties of molecules was the Hartree-Fock method [31,32,33,34]. Its appeal is that it preserves the concept of atomic orbitals, one-electron functions, describing the movement of the electron in the mean field of all other electrons. Although there are some inherent deficiencies in the method, especially those referred to the absence of correlation effects. Improvements have included the introduction of many-body perturbation theory by Mollet and Plesset (MP) [35] (MP2 to second-order MP4 to fourth order). The computer power required for Hartree-Fock methods makes their use prohibitive for molecules containing more than very few atoms. 

Structure-electron count relationship is a powerful tool to understand and predict the structure and electronic properties of molecules and solids. An electroncounting rule, similar to the Htickel 4n+2 rule, which connects benenoid aromatics to graphene, is developed for taking icosahedral through polycondensa-... 

The experimental datum of vibrational intensity has been generally neglected by most of the workers, because of the lack of a suitable model of interpretation. Its importance has been recently realized for the understanding of the electronic properties of molecules, and the attention of many workers is being re-focussed at this field [6]. 

The traditional method to study the electronic properties of molecules is based on describing the motion of individual electrons. The 1998 Nobel Chemistry Laureate, Walter Kohn, showed that it is not necessary to consider the motion of each individual electron. In other words, the system is characterized by its electron density rather than by a wave function. Due to its simplicity, we can study a very-large-molecule problem, such as the mechanism of enzymatic reac-... 

CASTEP uses DFT to calculate electronic properties of molecules, liquids, amorphous, and crystalline solids. 

Electrochemistry is a strong experimental tool for fundamental investigation and understanding of electronic properties of molecules (intramolecular interactions, extent of delocalization, relationship between structure and redox properties). Suitable electrochemical treatment reveals even very subtle features and irregularities, provokes questions, and suggests the answers. For their proof, combination with spectrometry and correlation with quantum chemistry is necessary. 

Most of the electronic properties of molecules and clusters depend on their shape and size. Even though there are varied definitions for shape and size of a species, a widely used definition is the MED topological one. Boyd has used the MED contour to discuss the relative sizes of atoms [49]. On the other hand for molecules, Bader et al. [32] proposed the surface of constant electron density (0.002 a.u.) to describe shape and size of diatomic molecules. Here in the present paper, for justifying the variation in polarizability and to quantify the delocalization of the valence electrons in these clusters, the volume enclosed within the 0.0001 a.u. MED isosurface is quantified. The MED contours at 0.01,0.001, and 0.0001 a.u. of the Lij, Li4, Na2, and Na4 are depicted in Eigure 11.8. The respective volume enclosed within the 0.0001 a.u. MED isosurfaces of lithium and sodium clusters with sizes ranging from 2 through 40 is reported in Table 11.7. 

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