an equation used in wave mechanics to describe a physical system. For a particle of mass m and potential energy V it is written (i h/2π).(∂ψ/∂ t) = (–h2/8π2m)∇2ψ + Vψ, where i = √–1, h is the Planck constant, t the time, ∇2 the Laplace operator, and ψ the wave function