Geometric momentum in the Monge parametrization of two dimensional   sphere
  A two dimensional surface can be considered as three dimensional shell whose thickness is negligible in comparison with the dimension of the whole system. The quantum mechanics on surface can be first formulated in the bulk and the limit of vanishing thickness is then taken. The gradient operator and the Laplace operator originally defined in bulk converges to the geometric ones on the surface, and the so-called geometric momentum and geometric potential are obtained. On the surface of two dimensional sphere the geometric momentum in the Monge parametrization is explicitly explored. Dirac's theory on second-class constrained motion is resorted to for accounting for the commutator [x_{i},p_{j}]=i \hbar({\delta}_{ij}-x_{i}x_{j}/r^2) rather than [x_{i},p_{j}]=i\hbar{\delta}_{ij} that does not hold true any more. This geometric momentum is geometric invariant under parameters transformation, and self-adjoint. 
D. M. Xun, and Q. H. Liu
math-ph math.MP quant-ph