Argon and potassium chloride

In the first test we optimised Lennard-Jones parameters for Ar, 

20 A (KCl). Convergence acceleration on the repulsive potential was not used In these tests. The dielectric constant was set to 1, and K and Cl were given the charges +1 and -1. The optimum was reached after 6 Iterations the results are given In Table 11-3  

In the second test we optimised also on the lattice energy of Argon, which Is -7 7 0 kJ mol (-1.850 kcal mol ). It was given a weight 0.3 times the weight of lattice constants. The optimum was reached after 7 Iterations the results are given In Table 11-3  

It Is seen that the Ar structure Is reproduced perfectly, the KCl structure to 40 /oo, and the lattice energy of Ar to 70 /oo. The restriction on parameters A and B forces K and Cl to be equal In the van der Waals sense, which leads to the Inaccuracy In lattice constant and consequently lattice energy of KCl. 

As a first test of optimisation on molecular crystals, we optim- 

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