  We propose a general method of constructing Wannier functions in disordered
systems directly out of energy eigenstates. This method consists of two
successive operations: (i) a phase transformation setting the proper
localization center; (ii) the mixing of adjacent states in energy to
sufficiently minimize the spread of the Wannier functions. The latter operation
can be well approximated by a band matrix, further facilitating the
calculation. Detailed implementation of our method is illustrated with one
dimensional systems; the generalization to higher dimensions is
straightforward.
