Lattice charge-dipole energy

Hirshfeld and Mirsky (1979) evaluated the relative contributions to the lattice energy for the crystal structures of acetylene, carbon dioxide, and cyanogen, using theoretical charge distributions. Local charge, dipole and quadrupole moments are used in the evaluation of the electrostatic interactions. When the unit cell dimensions are allowed to vary, inclusion of the electrostatic forces causes an appreciable contraction of the cell. In this study, the contributions of the electrostatic and van der Waals interactions to the lattice energy are found to be of comparable magnitude. 

The data bank presently has the following departments structure, frequency, charge, dipole moment more will be added as need arises, notably rotational constants, lattice energy and unit cell dimensions. 

Values for the partial charges of atoms can be derived from quantum mechanical calculations, from the molecular dipole moments and from rotation-vibration spectra. However, often they are not well known. If the contribution of the Coulomb energy cannot be calculated precisely, no reliable lattice energy calculations are possible. 

Energy calculations for ionic lattices show 6a = 1l6. Molten salts can form transient dipoles and multipoles as ion pairs and clusters, but it is unlikely that these contribute to a dielectric constant. For charge transfer in molten salts, the equivalent of an FC process is the change in electroneutrality length as valence changes. 

Consider a planar lattice of parallel dipoles oriented normal to the plane. The positive and negative charges of each dipole representing a zwitterionic head group are separated by a distance D, and the array is immersed in a medium of dielectric constant e. Let a denote the area of an elementary cell of the lattice, i.e., the area per dipole. The electrostatic interaction energy per dipole is then... 

---