Speaker: Federico Grasselli (SISSA, Trieste)

Abstract: The Green-Kubo theory of linear response[1] allows to extract the electric (ionic) conductivity of electronically insulating fluids from the time-correlation function of electric currents, in molecular dynamics simulations.
Standard methods to compute ab initio currents are based on the calculation of Born effective charge tensors of each atom at each time, a computationally demanding operation. Interestingly enough, the same results are obtained if Born tensors are replaced by integer oxidation numbers of the atoms[2].
In this talk I discuss how arguments from charge-transport quantization[3] and from a recently-formulated gauge-invariance principle of transport coefficients[4] can be employed to understand this strange coincidence, providing an alternative method to compute first-principle electric conductivity of ionic fluids.

[1] M. S. Green, J. Chem. Phys. 20(8), 1281–1295 (1952)
[2] M. French, S. Hamel, and R. Redmer, Phys. Rev. Lett. 107, 185901 (2011)
[3] D. J. Thouless, Phys. Rev. B 27, 6083 (1983)
[4] L. Ercole, A. Marcolongo, P. Umari, and S. Baroni, J. Low Temp. Phys. 185, 79–86 (2016)