where V e (q) is the extrapotential term resulting from the use of a non-Euclidean volume element dν ρ = ρ(q)dq 1 dq 2 . . . dq n . ρ(q) is a real positive function which has to be adapted so that the basis set be orthonormal. The quantities f ij 2 (q), f i 1 (q) and V e (q) in eq. ( ) are expressed as follows: