Molecular Mechanics

Molecular Mechanics is a computational method that computes the potential energy surface for a particular arrangement of atoms using potential functions that are derived using classical physics. These equations are known as a force-field.
Molecular Mechanics is based on several assumptions:
  1. It treats the electrons around a nucleus and a the nucleus itself as a perfect sphere.
  2. The bonds between molecules are treated as springs.
  3. Potential functions rely on experimental parameters such as force constants and equilibrium values.
  4. The potential energy function is the sum of individual functions for bond stretching, angle bending, torsional energies, and non-bonding interactions.
The potential functions generated by molecular mechanics have no absolute meaning but are simply for comparing different configurations of a molecule.
Advantages of Molecular Mechanics:
  • requires less of a computer than quantum mechanical methods.
Disadvantages of Molecular Mechanics:
  • restricted by parameters of equations(i.e. a different force-field for different types of atoms)
  • not applicable for electronic properties
Molecular Mechanics is Useful for:
  • large molecules such as proteins