Task: Text Categorization
Input (English): One equation used to calculate this quantity multiplies two terms with a sum of radii in their denominators, and is known as the Kapustinskii equation. A rough approximation of it can be found with a modified form of Coulomb's Law featuring a single distance, while a constant that is proportional to this quantity can be determined with the Evjen method or calculated by expanding cubes, and is named for Madelung. Another method used to determine it ends with gaseous ions in the Born-Haber cycle. For 10 points, name this quantity, like internal energy symbolized U, defined as the amount of energy needed to completely ionize a solid compound.
Output (English): Science