Some Observations Concerning Electronic Densities, Electrostatic Potentials and Chemical Potentials

The hypothesis that the electronic density distribution in a molecule is qualitatively similar to the nuclear potential is shown. to be in error in at least two cases-oxirane and cubane-although it does hold true in a\u27 number of other systems. Its emphasis upon the dominant role played by electrostatic internctions with the nuclei is consistent with some approximate molecular energy formulas. However, taking the nuclear potential as an approximation to the electronic density misses the small effects that correspond to the formation of chemical bonds. It is suggested that the electronic density difference function should provide a rough picture of the local variations in the chemical potential that occur as atoms combine to form a molecule. Finally, the common practice of representing the energy and electronegativity of an interacting atom as functions only of the number of electrons associated with the atom is shown to be ina\u27dequate; some account should be taken of the changing internuclear separations

Molecular Surfaces, van der Waals Radii and Electrostatic Potentials in Relation to Noncovalent Interactions

We investigate two questions relating to the use of electrostatic potentials in interpreting and predicting noncovalent interactions. First, is the molecular surface defined by the 0.001 au contour of the electronic density a reasonable one, in terms of its relationship to the van der Waals radii of the component atoms? Second, how does the electrostatic potential vary with distance in different directions from the nuclei of covalently-bonded atoms? We address these questions computationally, at the density functional B3PW91/6-31G(d,p) level

Looking for Gluon Substructure at the Tevatron

The impact of nonrenormalizable gluon operators upon inclusive jet cross sections is studied. Such operators could arise in an effective strong interaction Lagrangian from gluon substructure and would induce observable cross section deviations from pure QCD at high transverse jet energies. Comparison of the theoretical predictions with recent CDF data yields a lower limit on the gluon compositeness scale $\Lambda$. We find \Lambda > 2.03 \TeV at $95\%$~CL.Comment: 12 pages with 2 figures not included but available upon request, CALT-68-1872, HUTP-93/A01

Variation of parameters in Becke‐3 hybrid exchange‐correlation functional

We have investigated the consequences of varying the three parameters in Becke's hybrid exchange‐correlation functional, which includes five contributions: Hartree–Fock exchange, local exchange, Becke's gradient exchange correction, local correlation, and some form of gradient correlation correction. Our primary focus was upon obtaining orbital energies with magnitudes that are reasonable approximations to the electronic ionization potentials; however, we also looked at the effects on molecular geometries and atomization enthalpies. A total of 12 parameter combinations was considered for each of three different gradient correlation corrections: the Lee–Yang–Parr, the Perdew‐86, and the Perdew–Wang 91. Five molecules were included in the study: HCN, N2, N2O, F2O, and H2O. For comparison, a Hartree–Fock calculation was also carried out for each of these. The 6‐31+G** basis set was used

Molecular dynamics simulations of liquid nitromethane

A potential energy function with harmonic intramolecular and Lennard-Jones plus Coulombic intermolecular terms was tested in molecular dynamics simulations of liquid nitromethane. Parameter values were adjusted iteratively until satisfactory agreement with density functional pair calculations and experimental data was achieved. The properties computed using the NVT and NPT ensembles were the heat of vaporization, dielectric constant, self-diffusion coefficient, density, heat capacity at constant pressure, pair correlation functions, single molecule and collective dipole moment reorientation times, the vibrational spectrum, and the effect of increasing pressure upon the C−N stretching frequency. Overall, the results were in reasonable accord with experimental results, the greatest discrepancy being for the dielectric constant. It was concluded, on the basis of the reorientation times and the calculated molecular

Colour Charges and the Anti-Screening Contribution to the Interquark Potential

Asymptotic freedom arises from the dominance of anti-screening over screening in non-abelian gauge theories. In this paper we will present a simple and physically appealing derivation of the anti-screening contribution to the interquark potential. Our method allows us to identify the dominant gluonic distribution around static quarks. Extensions are discussed.Comment: 7 pages, LaTe

Some Observations Concerning Electronic Densities, Electrostatic Potentials and Chemical Potentials

The hypothesis that the electronic density distribution in a molecule is qualitatively similar to the nuclear potential is shown. to be in error in at least two cases-oxirane and cubane-although it does hold true in a\u27 number of other systems. Its emphasis upon the dominant role played by electrostatic internctions with the nuclei is consistent with some approximate molecular energy formulas. However, taking the nuclear potential as an approximation to the electronic density misses the small effects that correspond to the formation of chemical bonds. It is suggested that the electronic density difference function should provide a rough picture of the local variations in the chemical potential that occur as atoms combine to form a molecule. Finally, the common practice of representing the energy and electronegativity of an interacting atom as functions only of the number of electrons associated with the atom is shown to be ina\u27dequate; some account should be taken of the changing internuclear separations

Halogen bonding in hypervalent iodine and bromine derivatives: Halonium salts

Halogen bonds have been identified in a series of ionic compounds involving bromonium and iodonium cations and several different anions, some also containing hypervalent atoms. The hypervalent bromine and iodine atoms in the examined compounds are found to have positive Ï\u83-holes on the extensions of their covalent bonds, while the hypervalent atoms in the anions have negative Ï\u83-holes. The positive Ï\u83-holes on the halogens of the studied halonium salts determine the linearity of the short contacts between the halogen and neutral or anionic electron donors, as usual in halogen bonds