  Anisotropy of interfacial energy is the principal driving force for material
microstructure evolution yet its origins remain uncertain and a quantitative
description lacking. We present and justify a concise hypothesis on the
topography and topology of the functional space of grain boundary energies and,
based on this hypothesis, construct a closed-form function that quantitatively
describes energy variations in the entire 5-space of macroscopic parameters
defining grain boundary geometry. The new function is found to be universal for
the crystallography class of face-centered cubic metals.
