where V ^ ^ = V ( r 1 , r 2 , … … , r N , t ) , is the potential energy function, now a function of the spatial configuration of the system and time (a particular set of spatial positions at some instant of time defines a configuration) and T ^ ^ n = p ^ ^ n ⋅ ⋅ p ^ ^ n 2 m n = − − ℏ ℏ 2 2 m n ∇ ∇ n 2 is the kinetic energy operator of particle n , ∇ ∇ n is the gradient for particle n , and ∇ ∇ n 2 is the Laplacian for particle n : ∇ ∇ n 2 = ∂ ∂ 2 ∂ ∂ x n 2 + ∂ ∂ 2 ∂ ∂ y n 2 + ∂ ∂ 2 ∂ ∂ z n 2 ,