Force Field Methods

• Too expensive to solve QM electronic energy for every nuclear configuration

• Instead define energy using simple empirical formulas

  • “force fields” or “molecular mechanics”

• Decomposition of the total energy

• Force fields usually written in terms of pairwise additive interatomic potentials

  • with some exceptions

Single-atom energy(external field)

Atom-pair contribution

3-atom contribution

Neglect 3- and higher-order terms

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