The expression for total potential energy is given by, π= U+H

Differentiating above equation δπ= δU+δH

In principle of virtual work δU=δH δπ = 0

Hence we can conclude that a deformable body is in equilibrium when the potential energy is having stationary value.

Hence the principle of minimum potential energy states among all the displacement equations that internal compatibility and the boundary condition those that also satisfy the equation of equilibrium make the potential energy a minimum is a stable system