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Atomic separation

It is noteworthy that it is not obligatory to use a torsional potential within a PEF. Depending on the parameterization, it is also possible to represent the torsional barrier by non-bonding interactions between the atoms separated by three bonds. In fact, torsional potentials and non-bonding 1,4-interactions are in a close relationship. This is one reason why force fields like AMBER downscale the 1,4-non-bonded Coulomb and van der Waals interactions. [Pg.343]

Fhe van der Waals and electrostatic interactions between atoms separated by three bonds (i.c. the 1,4 atoms) are often treated differently from other non-bonded interactions. The interaction between such atoms contributes to the rotational barrier about the central bond, in conjunction with the torsional potential. These 1,4 non-bonded interactions are often scaled down by an empirical factor for example, a factor of 2.0 is suggested for both the electrostatic and van der Waals terms in the 1984 AMBER force field (a scale factor of 1/1.2 is used for the electrostatic terms in the 1995 AMBER force field). There are several reasons why one would wish to scale the 1,4 interactions. The error associated wilh the use of an repulsion term (which is too steep compared with the more correct exponential term) would be most significant for 1,4 atoms. In addition, when two 1,4... [Pg.229]

The attraction for two neutral atoms separated by more than four Angstroms is approximately zero. The depth of the potential wells is minimal. For the AMBER force field, hydrogen bonds have well depths of about 0.5 kcal/mol the magnitude of individual van der Waals well depths is usually less. [Pg.27]

A convenient classification scheme for reactions of this general type expressed below focuses attention on the number of atoms separating the two reactive centers in each component. [Pg.122]

For bicyclic structures the von Baeyer name consists of the prefix bicyclo-, followed in square brackets by the numbers of carbon atoms separating the bridgeheads on the three possible routes from one bridgehead to the other, followed in turn by the name of the alkane (or other homogeneous hydride, or repeating unit hydride) containing the same number of atoms in the chain as the whole bicyclic skeleton (examples 55-57). Replacement nomenclature can be applied to hydrocarbon names (example 58). [Pg.25]

Vibrational energy, which is associated with the alternate extension and compression of die chemical bonds. For small displacements from the low-temperature equilibrium distance, the vibrational properties are those of simple harmonic motion, but at higher levels of vibrational energy, an anharmonic effect appears which plays an important role in the way in which atoms separate from tire molecule. The vibrational energy of a molecule is described in tire quantum theory by the equation... [Pg.44]

Table 45.1. Partial structures from the CH COSY and CH COLOC plots (the protons are given in Italic numerals, C atoms separated by a single bond are given in bold numerals and C atoms separated by two or three bonds... Table 45.1. Partial structures from the CH COSY and CH COLOC plots (the protons are given in Italic numerals, C atoms separated by a single bond are given in bold numerals and C atoms separated by two or three bonds...
Partial structure Protons Sh CH a one bond Sc C Sc atoms separated by two or three bonds Sc Sc Sc Sc Sc... [Pg.233]

Table 4.1 Hydrogen molecule with infinite atomic separation electron 1 associated with nucleus A, electron 2 associated with nucleus B... Table 4.1 Hydrogen molecule with infinite atomic separation electron 1 associated with nucleus A, electron 2 associated with nucleus B...
In the limit of infinite atom separations, or if we switch off the Coulomb repui. sion between two electrons, all four wavefunctions have the same energy. But they correspond to different eigenvalues of the electron spin operator the first combination describes the singlet electronic ground state, and the other three combinations give an approximate description of the components of the first triplet excited state. [Pg.92]

Torsional angles around sp hybridized atoms separated by 120°. [Pg.415]

On the other hand the Thomas-Fermi method, which treats the electrons around the nucleus as a perfectly homogeneous electron gas, yields a mathematical solution that is universal, meaning that it can be solved once and for all. This feature already represents an improvement over the method which seeks to solve Schrodinger equation for every atom separately. This was one of the features that made people go back to the Thomas-Fermi approach in the hope of... [Pg.103]

Here, Wj is the number of neighboring atoms at the distance d,. Because the atoms separated by more than twice the shortest interatomic distance cannot be counted as neighboring, the summation is Hmited only to the interatomic distances less than twice dg. Without this limitation, calculation of the parame-... [Pg.31]


See other pages where Atomic separation is mentioned: [Pg.139]    [Pg.1371]    [Pg.353]    [Pg.69]    [Pg.522]    [Pg.925]    [Pg.35]    [Pg.102]    [Pg.5]    [Pg.407]    [Pg.242]    [Pg.318]    [Pg.138]    [Pg.255]    [Pg.122]    [Pg.123]    [Pg.159]    [Pg.230]    [Pg.239]    [Pg.142]    [Pg.135]    [Pg.522]    [Pg.925]    [Pg.1215]    [Pg.199]    [Pg.106]    [Pg.180]    [Pg.100]    [Pg.248]    [Pg.111]    [Pg.222]    [Pg.79]    [Pg.250]    [Pg.226]    [Pg.100]    [Pg.197]   
See also in sourсe #XX -- [ Pg.58 , Pg.81 ]




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