Hellman-Feynman theorem

Hellman-Feynman theorem

[¦hel·mən ¦fīn·mən ‚thir·əm]
(quantum mechanics)
A theorem which states that in the Born-Oppenheimer approximation the forces on nuclei in molecules or solids are those which would arise electrostatically if the electron probability density were treated as a static distribution of negative electric charge.