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Unformatted text preview: R P I Another part where we may need to replace the original potential is at the shortest interatomic distances. I In most analytic potentials the repulsive part simply allows having the potential minimum at correct place. I It also gives a proper description of the near-equilibrium system when the interatomic distance is somewhat smaller than the ideal dimer distance. I However, as we saw for pair potentials, they usually give wrong description of the energy when the atoms are very close to each other. I This typically happens in ion irradiation or nuclear physics, or when other energetic phenomena are involved. I Therefore, there is a need to use a repulsive potential at these short distances fitted smoothly to the equilibrium potential. Notes I The usual equation for a repulsive potential is U ( r ) = Z 1 Z 2 e 2 4 r ( r a ) (32) where ( x ) is a screening function and a = a ( Z 1 , Z 2 ) is a screening length....
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- Winter '12