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!!!!!  VERIFICATION CHECK: vc-forces-numerical-derivative  !!!!!
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Description: Comparison of the analytical forces obtained from the model with
             forces computed by numerical differentiation using Richardson
             extrapolation for a randomly distorted non-periodic structure based
             off the equilibrium face-centered cubic (fcc) structure. Separate
             configurations are tested for each species supported by the model,
             as well as one containing a random distribution of all species.
             Configurations used for testing are provided as auxiliary files.

Author: Ellad Tadmor