Molecular Applications Group

Levitt M (1990) Energy calculations and dynamics program. Molecular Applications Group, Standford and Yeda, Behovot, Israel... 

Molecular Applications Group Dr. Michael Levitt 880 Lathrop Drive... 

Molecular Applications Group 445 Sherman Avenue, Suite T Palo Alto, CA 94306, U.S.A. 

A. Sali and T. L. Blundell, J. Mol. Biol., 1993, 234, 779-815. MAG. LOOK , Molecular Applications Group, Palo Alto, CA. R. B. Altman and M. Gerstein, in Second International Conference on Intelligent Systems for Molecular Biology , 1994. 

Applications of neural networks are becoming more diverse in chemistry [31-40]. Some typical applications include predicting chemical reactivity, acid strength in oxides, protein structure determination, quantitative structure property relationship (QSPR), fluid property relationships, classification of molecular spectra, group contribution, spectroscopy analysis, etc. The results reported in these areas are very encouraging and are demonstrative of the wide spectrum of applications and interest in this area. 

Per-Olov Lowdin had a long and lasting interest in the analytical methods of quantum mechanics and my tribute to his legacy involves an application of the Wentzel-Kramers-Brillouin (WKB) asymptotic approximation method. It was the subject of a contribution(l) by Lowdin to the Solid State and Molecular Theory Group created by John C. Slater at the Massachusetts Institute of Technology. 

It is often convenient to use the symmetry coordinates that form the irreducible basis of the molecular symmetry group. This is because the potential-energy surface, being a consequence of the Born-Oppenheimer approximation and as such independent of the atomic masses, must be invariant with respect to the interchange of equivalent atoms inside the molecule. For example, the application of the projection operators for the irreducible representations of the symmetry point group D3h (whose subgroup... 

Stone applied the theory of Longuet-Higgins to deduce the character tables for the multiple internal rotation in neopentane and in octahedral hexa-ammonium metallic complexes [6]. Dalton examined the use of the permutation-inversion groups for determining statistical weights and selection rules for radiative processes in non-rigid systems [7]. Many applications of the Molecular Symmetry Groups have been reviewed later by Bunker [8,9]. 

The Group Theory Calculator [the GT Calculator] is the set of interactive EXCEL spreadsheet files, one for each of the main molecular point groups, on the CDROM supplied with this manual. The group theoretical calculations, which can be performed with the calculator, are rendered possible because of the enhancement of the basic spreadsheet operations and displays using Visual Basic for Applications code and the complex-arithmetic routines available in the Analysis Tool Pack EXCEL Add-ins . Since the Analysis Tool Pack is not one of the standard components loaded in a typical installation of the EXCEL software package, it is necessary, before attempting to use the GT Calculator, to ensure that your version of the EXCEL programme includes this extra component. With any spreadsheet open, check the Add-ins list in the TOOLS menu on the main EXCEL toolbar and, if necessary, install this component in the usual way. 

The theorems described in section 3.2 provide for the ready calculation of the r , and Fs reducible characters, generated by the transformation properties of s, p and d-atomic orbitals distributed over the vertices of the structure orbits of the various point groups, which decompose into the direct sums of irreducible components listed in Tables 3.1 to 3.4. Application of the theorems requires the identification of sufficient numbers of central harmonics to act as basis functions for the irreducible components of the regular orbits of these molecular point groups. 

The average local ionization energy 7(r) has many interesting and significant aspects and applications. It is related to local temperature and atomic shell structure, it is linked to electronegativity and shows promise as a measure of local polarizability. It permits the characterization of bonds and radical sites, and - in conjunction with volume -the prediction of molecular and group polarizabilities. Finally, it is an effective guide to reactivity towards electrophiles, especially when complemented by the electrostatic potential. All of these areas continue to be studied. 

Finally it is appropriate to comment on the relationship between GO s and united atom orbitals (75). A canonical GO can be considered to be the angular part of the corresponding united atom orbital. However, the properties of GO s are of general applicability whereas the united atom orbitals are actually poor models for valence MO s. This is so because the GO concept represents a simple embodiment of the representational properties of the molecular point group, whereas the united atom concept contains additional detail resulting from a relatively poor physical model designed to simplify the description of the interactions between nuclei and electrons. Consequently united atom orbitals have very specific radial nodal structures. These nodes are unrealistic, are irrelevant for our purposes, and can only be deduced once the united atom MO approximation is known. By contrast we have shown that canonical GO s can be used to construct canonical MO s. 

When selective information about the surface is desired, the MAS experiment is often combined with cross-polarization. Such applications take advantage of the fact that the surface generally contains hydroxyl or molecular H2O groups, which in the presence of an external magnetic field represent a large reservoir of H magnetization. Cross-polarization employs strong double irradiation at the Hart-mann-Hahn condition (27,281... 

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