NaCl lattice, force constant

Obviously, the addition of the values of all interaction force constants which are involved in F(lattice) simplify the result F(lattice) w /. Analogous relations between F(lattice) and the observed frequencies have been discussed for solid NaCl and Cap2 (Becher,... 

The Madelung constant takes into account the different Coulombic forces, both attractive and repulsive, that act on a particular ion in a lattice. In the NaCl lattice, six Cl atoms surround each Na " atom. The coordination number —6 describes the number of atoms which surround the selected reference atom. X-ray analysis indicates that each atom is a distance of 281 pm from its nearest neighbour. To calculate the Madelung constant we consider the four unit cells that surround the selected reference atom. Firstly there are twelve Cl ions each at a distance a from the central ion, and the Cff ions repel one another. The distance a is related to r by the equation... 

Here k is the force constant of the chemical bonds in the NaCl lattice, with the dimensions of N/m, and a is the respective lattice parameter in m. Note the ratio of these microscopic constants has the dimensions of N/m, or... 

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