Extended-range computation of Wannier-like functions in amorphous semiconductors

We have computed first-principles occupied Wannier-like functions within an unprecedented spatial range in a realistic model of amorphous Si containing 4096 atoms. To avoid the computation of eigenstates we applied the O(N) Fermi-operator expansion method. The functions decay exponentially in space in a fashion similar to the best-localized occupied Wannier states in crystalline silicon. While their decay lengths do not depend on the local distortions, the functions have an intricate nonspherical structure depending on the disorder in the material.