Charges, electrostatic

The Pullman method is a combination of the Del Re method for computing the a component of the charge and a semiempirical Hrickel calculation for the 7t portion. It has been fairly successful in describing dipole moments and atomic charges for nucleic acids and proteins. 

The Q-equilibrate method is applicable to the widest range of chemical systems. It is based on atomic electronegativities only. An iterative procedure is used to adjust the charges until all charges are consistent with the electronegativities of the atoms. This is perhaps the most often used of these methods. 

There are cases where each of these methods excels. However, the literature does indicate a preference for certain methods that obtain the most consistent results. Below are some of the suggestions based on a review of the literature  

For molecular mechanics, the charge calculation method used in parameterizing the force field should be used if possible. Otherwise, use Q-equilibrate or electrostatic charges. 

For examining the interactions between molecules, use electrostatic charges. 

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Hydrocarbons generally have very low electrical conductivities and manipulation of these fluids creates electrostatic charges that can result in fire or explosions. This problem is encountered with gasoline and kerosene. 

Singh U C and Kollman P A 1984 An approach to computing electrostatic charges for molecules J. Comput. Chem. 5 129... 

The most elementary mean-field models of electronic structure introduce a potential that an electron at r would experience if it were interacting with a spatially averaged electrostatic charge density arising from the N- 1 remaining electrons ... 

Particularly in polar solvents, electrostatic charges usually have an important contribution to tire particle interactions. We will first discuss tire ion distribution near a single surface, and tlien tire effect on interactions between two colloidal particles. 

AS )) the function to be minimized is exp (-AS p/R)/ [36]. A quantitative expression for AS can be found by noting that the A monomers in an unstrained loop (N > 4) have essentially two possible confonnations, pointing either inwards or outwards. For loops smaller than a critical size the inward ones are in an apolar environment, since the enclosed water no longer has bulk properties, and the outward ones are in polar bulk water hence the electrostatic charges on... 

MM+ calculations do not usually have an electrostatic charge-charge interaction nor define a set of atomic charges for atoms. 

Singh U C and P A Kollman 1984. An Approach to Computing Electrostatic Charges for Molecules, Journal of Computational Chemistry 5 129-145. 

The energy of solvation can be further broken down into terms that are a function of the bulk solvent and terms that are specifically associated with the first solvation shell. The bulk solvent contribution is primarily the result of dielectric shielding of electrostatic charge interactions. In the simplest form, this can be included in electrostatic interactions by including a dielectric constant k, as in the following Coulombic interaction equation ... 

The properties available include electrostatic charges, multipoles, polarizabilities, hyperpolarizabilities, and several population analysis schemes. Frequency correction factors can be applied automatically to computed vibrational frequencies. IR intensities may be computed along with frequency calculations. 

Wave functions can be visualized as the total electron density, orbital densities, electrostatic potential, atomic densities, or the Laplacian of the electron density. The program computes the data from the basis functions and molecular orbital coefficients. Thus, it does not need a large amount of disk space to store data, but the computation can be time-consuming. Molden can also compute electrostatic charges from the wave function. Several visualization modes are available, including contour plots, three-dimensional isosurfaces, and data slices. 

Antistatic agents require ambient moisture to function. Consequently their effectiveness is dependent on the relative humidity. They provide a broad range of protection at 50% relative humidity. Much below 20% relative humidity, only materials which provide a conductive path through the bulk of the plastic to ground (such as carbon black) will reduce electrostatic charging. 

Electroslag Electroslag welding Electrospray Electrostatic atomizer Electrostatic charges... 

Mechanisms of Leukocyte Adsorption. The exact mechanism of leukocyte adhesion to filter media is not yet fuUy understood. Multiple mechanisms simultaneously contribute to the adhesion of cells to biomaterials, however, physical and biological mechanisms have been distinguished. Physical mechanisms include barrier phenomenon, surface tension, and electrostatic charge biological mechanisms include cell activation and cell to cell binding. 

Water and Waste Water Treatment. PAG products are used in water treatment for removal of suspended soHds (turbidity) and other contaminants such as natural organic matter from surface waters. Microorganisms and colloidal particles of silt and clay are stabilized by surface electrostatic charges preventing the particles from coalescing. Historically, alum (aluminum sulfate hydrate) was used to neutralize these charges by surface adsorption of Al cations formed upon hydrolysis of the alum. Since 1983 PAG has been sold as an alum replacement in the treatment of natural water for U.S. municipal and industrial use. 

Inks for continuous ink-jet printers typically comprise dyes dissolved in water or solvent having salts added to make the ink conductive for electrostatic charging. Whenever waterproof printing is required, low boiling solvent inks ate used. For printers that ate used in office environments, water is used as the ink solvent. Using water-based inks, humectants may be added to inhibit drying of ink in the sump and surfactants ate added to wet the printing surface. 

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