Kimika Teorikoa Seminar: Redefining the dielectric response of nanoconfined liquids: insights from water

Recent experiments show that the relative dielectric constant of water confined to a film of nanometric thickness reaches a strikingly low value of 2.1, barely above the bulk's 1.8 value for the purely electronic response [1]. We argue that the relative dielectric constant is not a well-defined measure for dielectric properties at sub-nanometer scales due to the ambiguous definition of confinement width. Instead, we propose the 2D polarisability as the appropriate, well-defined response function whose magnitude can be directly obtained from both measurements and computations. Our molecular-dynamics computations based on density-functional theory and empirical force fields reproduce the previously reported dielectric response of confined water, and importantly indicate a significant reduction, ~ 30%, of the electronic response as compared with the bulk's, contrary to what is widely assumed [2]. These results highlight the importance of accounting for electronic degrees of freedom when interpreting the dielectric response of polar fluids under nanoconfinement conditions.

[1] L. Fumagalli, A. Esfandiar, R. Fabregas, S. Hu, P. Ares, A. Janardanan, Q. Yang, B. Radha, T.Taniguchi, K.
Watanabe, G. Gomila, K. S. Novoselov, A. K. Geim (2018). Anomalously low dielectric constant of confined water. Science, 360(6395), 1339-1342.
[2] J. Zubeltzu, F. Bresme, M. Dawber, M. Fernandez-Serra, and E. Artacho (2025). Redefining the dielectric response of
nanoconfined liquids: insights from water. arXiv preprint arXiv:2412.01347.