Dielectric permittivity of a vacuum

Note that e is the relative dielectric constant, i.e., relative to the absolute dielectric constant (also called dielectric permittivity) of a vacuum, so, which equals 8.854 10 12 C V-1 m-1. 

N is the number of point charges within the molecule and Sq is the dielectric permittivity of the vacuum. This form is used especially in force fields like AMBER and CHARMM for proteins. As already mentioned, Coulombic 1,4-non-bonded interactions interfere with 1,4-torsional potentials and are therefore scaled (e.g., by 1 1.2 in AMBER). Please be aware that Coulombic interactions, unlike the bonded contributions to the PEF presented above, are not limited to a single molecule. If the system under consideration contains more than one molecule (like a peptide in a box of water), non-bonded interactions have to be calculated between the molecules, too. This principle also holds for the non-bonded van der Waals interactions, which are discussed in Section 7.2.3.6. 

The dielectric constant (permittivity) tabulated is the relative dielectric constant, which is the ratio of the actual electric displacement to the electric field strength when an external field is applied to the substance, which is the ratio of the actual dielectric constant to the dielectric constant of a vacuum. The table gives the static dielectric constant e, measured in static fields or at relatively low frequencies where no relaxation effects occur. 

The insulating property of any insulator will break down in a sufficiently strong electric field. The dielectric strength is defined as the electric strength (V/m) which an insulating material can withstand. For plastics the dielectric strength can vary from 1 to 1000 MV/m. Materials may be compared on the basis of their relative permittivity (or dielectric constant). This is the ratio of the permittivity of the material to the permittivity of a vacuum. The ability of a... 

The calculation of lattice energies (and other Coulomb s law energies) is complicated somewhat by the fact that in SI the permittivity (dielectric constant) of a vacuum is no longer defined as one but has an experimentally determined value. Furthermore, for reasons we need not explore at present. Coulomb s law is stated in the form ... 

The dielectric constant (or relative permittivity) is usually expressed using the symbol c. The dielectric e is defined as the ratio of electric fields EJE for a vacuum and a substance placed between the plates of a capacitor. The dielectric constant of a vacuum is 1 and substances that can orient to greater or lesser extents in the applied field will have higher dielectric constants. The dielectric constant of heptane at 20°C is 1.9. Acetonitrile, CH3C=N , has a dielectric constant at 20°C of 37.5. The dielectric constant for water is near 80. 

The permittivity of a material is the constant e in the rationalised expression, F = (0i02)/(47rer2), where F is the force between charges Q and 02 separated by a distance r. The permittivity of a vacuum <6 according to this definition is equal to 8.854 x 1012 kg m 3 s4 A2. The dielectric constant of a material is equal to the ratio between its permittivity and the permittivity of a vacuum, and is a dimensionless quantity. 

---