Muffin Tin Orbitals of Arbitrary Order
  We have derived orbital basis sets from scattering theory. They are expressed as polynomial approximations to the energy dependence of a set of partial waves, in quantized form. The corresponding matrices, as well as the Hamiltonian and overlap matrices, are specified by the values on the energy mesh of the screened resolvent and its first energy derivative. These orbitals are a generalization of the 3rd-generation linear MTOs and should be useful for electronic-structure calculations in general. 
O.K. Andersen and T. Saha-Dasgupta