State Orthogonalization by Building a Hilbert Space: A New Approach to   Electronic Quantum Transport in Molecular Wires
  Quantum descriptions of many complex systems are formulated most naturally in bases of states that are not mutually orthogonal. We introduce a general and powerful yet simple approach that facilitates solving such models exactly by embedding the non-orthogonal states in a new Hilbert space in which they are by definition mutually orthogonal. This novel approach is applied to electronic transport in molecular quantum wires and is used to predict conductance antiresonances of a new type that arise solely out of the non-orthogonality of the local orbitals on different sites of the wire. 
Eldon Emberly and George Kirczenow