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The energy criterion associated with Frederick Charles Frank states that, for dislocations of comparable length with approximately common line-energy factors, a reaction conserving Burgers vector is energetically favourable when the displayed inequality holds. The rule is an energy estimate, not a proof that the geometry or kinetic barriers permit the reaction. Edge/screw character, elastic anisotropy and changed lengths refine it.

Frederick Charles Frank helped develop the theory of dislocations and crystal growth. A dislocation can influence how new atomic layers form at a crystal surface, linking a defect inside a solid to its growth behaviour. The University of Bristol's history identifies these fields, together with surface physics, as major parts of his work.^[ref]