Electron topology

ELECTRONIC TOPOLOGICAL TRANSITIONS AND COMPOSITIONAL ORDER IN CiiPd AND CuPt ALLOYS... 

I.A.Abrikosov, Yu.H.Vehkov, P.A.Korzhavyi, A.V.Ruban and L.E.Shilkrot, Ab-initio calculations of the electronic topological transition in Li-Mg alloys , Sohd State Commun. 83 867 (1992) ... 

Hall, L. H., Kier, L. B. Electrotopological state indices for atom types a novel combination of electronic, topological and valence state information. J. Chem. Inf. Comput. Sd. 1995, 35, 1039-1045. 

Figure 1 2 1. The different types of 2.5 Lifshitz electronic topological transition (ETT) The upper panel shows the type (I) ETT where the chemical potential EF is tuned to a Van Hove singularity (vHs) at the bottom (or at the top) of a second band with the appearance (or disappearance) of a new detached Fermi surface region. The lower panel shows the type (II) ETT with the disruption (or formation) of a neck in a second Fermi surface where the chemical potential EF is tuned at a vHs associated with the gradual transformation of the second Fermi surface from a two-dimensional (2D) cylinder to a closed surface with three dimensional (3D) topology characteristics of a superlattice of metallic layers...

I. B. Bersuker+ and A. S. Dimoglo, The Electron-Topological Approach to the QSAR Problem. 

Connection Spatial arrangement Effective nuclear Electron (Topology) (Symmetry) potentials distribution... 

Recent developments include 3D QSAR methods which relate regions of the binding site with complementary properties1471. The conformation of each molecule then needs be computed and the descriptor property determined. Another interesting development is the Electron Topological (ET) approach in QSAR meth-ods[48]. Molecular compounds are described by quadratic matrices (n2, n number of atoms), where elements close to the diagonal represent electronic parameters while the other elements are related to the structure. 

Linear and non-linear correlations of structural parameters and strain energies with various molecular properties have been used for the design of new compounds with specific properties and for the interpretation of structures, spectra and stabilities 661. Quantitative structure-activity relationships (QSAR) have been used in drug design for over 30 years 2881 and extensions that include information on electronic features as a third dimension (the electron topological approach, ET) have been developed and tested 481 (see Section 2.3.5). Correlations that are used in the areas of electron transfer, ligand field properties, IR, NMR and EPR spectroscopy are discussed in various other Chapters. Here, we will concentrate on quantitative structure-property relationships (QSPR) that involve complex stabilities 124 289-2911. 

Boyd, Eds., VCH Publishers, New York, 1991, Vol. 2, pp. 367-422. The Molecular Connectivity Chi Indexes and Kappa Shape Indexes in Structure-Property Modeling. I. B. Bersuker and A. S. Dimoglo, in Reviews in Computational Chemistry, K. B. Lipkowitz and D. B. Boyd, Eds., VCH Publishers, New York, 1991, Vol. 2, pp. 423 60. The Electron-Topological Approach to the QSAR Problem. 

Number of 3i-electrons Topological type of system Character of system... 

Dimoglo AS, Beda AA, Shvets NM, Gorbachov MY, Kheifits LA, Aulchenko IS. Investigation of the relationship between sandalwood odor and chemical structure electron-topological approach. New J. Chem. 1995 19 149-154. 

Bersuker and Dimoglo (455) described a matrix-based approach that combines geometric and electronic features of a molecule, the electron-topological approach. For each molecule, an electron-topological matrix of congru-ity (ETMC) is constructed based on a con-former selected by conformational analysis. 

Figure 3.47. The electron-topological matrix of congruity (ETMC) for a 17-atom fragment proposed by Bersuker and Dimoglo (455) to encode geometrical and electronic features of molecules.

Very similar to the electronic-topological descriptors, electron charge density connectivity index is defined for an - H-depleted molecular graph in which net atomic charges, calculated by computational chemistry, are used as weights for vertices [Estrada and Montero, 1993 Estrada, 1995d] ... 

For each molecule with A atoms, the square symmetric Ax A matrix, called the electron-topological matrix of congruity ETMC, is defined as the following ... 

By comparing the ETMC matrices of all the active compounds with those of the inactive ones, the electron-topological submatrix of activity ETSA is derived which contains matrix elements that are present in all the active compounds and absent from the inactive ones. The information contained in this matrix allows the design of new active compounds as well as the screening of several compounds with respect to their activity. 

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