Amorphous WO3: a first-principles approach

Results of first-principles calculations on the structure and electronic st ructure of amorphous WO3 are presented. The effect of non-stoichiometry is investigated. In particular, we discuss the pairing of W5+ species in oxyge n-deficient films resulting in deep in-gap states and its possible conseque nces for the electrochromic coloration efficiency. To this end, we make a c onnection with Raman experiments by calculating the vibrational density fro m molecular-dynamics simulation. For the W5+ -W5+ stretch we find a low fre quency mode at similar to 200 cm(-1) which agrees well with the Raman data. We also estimate the stability of isolated W5+ species in stoichiometric a nd oxygen-deficient tungstentrioxide. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.