This question is generated by my attempt to answer this one. I thought I could demonstrate that electronic conduction in water is possible because of the impact of an electric field on the band structure, but I am being hit with comments questioning the existence of band structure in liquids. I thoughtot was self-evident, but I was asked for references showing water has a band structure and what I am coming up with does not appear to be working (the comments are getting more upvotes than my answer). So I need help. Can anybody come up with more clear-cut references demonstrating that water, or liquids generally, has such a band structure?


1 Answer 1


do Couto et al have published an article [1] characterizing the density of states (band structure) of water using DFT theory combined with MC sampling. Extrapolating from clusters to bulk water, the HOMO-LUMO gap is 8.55 eV (Table 3).

From the abstract:

By extrapolating the results for larger clusters the threshold energy for photoelectron emission is $9.6±0.15 eV$ free clusters and $10.58±0.10 eV$ embedded clusters. Our results for the electron affinity $V_0=−0.17±0.05 eV$ and adiabatic band gap $E_{G,Ad}=6.83±0.05 eV$ of liquid water are in excellent agreement with recent information from theoretical and experimental works.

From the introduction:

It is generally accepted that water canbe described as a very large band-gap amorphous semiconductor.11,17 However, it is not obvious that the band-gap of liquid water can be uniquely associated with an optical vertical excitation process, where the gap is defined simply as the highest occupied molecular orbital-lowest unoccupied molecular orbital HOMO-LUMO energy difference. As recently pointed out by Coeet al.,3 the reactive nature of electronically excited water molecules,18 the reorganization of water molecules around charged species in liquid phase, and the observed photophysics of anionic defects known as the anion problem 4 strongly indicate that an adiabatic route can be defined for accessing the conduction-band edge in liquid phase. Moreover, given that the time scale ofthe solvent relaxation is much larger than the vertical process, the adiabatic band gap of liquid water cannot be determined vertically.

Reference [1] Cabral do Couto, Estácio, and Costa Cabral J. Chem. Phys.123, 0545102005

  • 1
    $\begingroup$ Great, just what I needed! $\endgroup$ Feb 9, 2019 at 23:28

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