(American Institute of Physics (AIP), 2020-05-07) Duque Zumajo, Diego; Torre Rodríguez, Jaime Arturo de la; Español Garrigos, José; https://orcid.org/0000-0001-7055-5835; https://orcid.org/0000-0002-1657-0820
We study through MD simulations the correlation matrix of the discrete transverse momentum density field in real space for an unconfined Lennard-Jones fluid at equilibrium. Mori theory predicts this correlation under the Markovian approximation from the knowledge of the non-local shear viscosity matrix, which is given in terms of a Green–Kubo formula. However, the running Green–Kubo integral for the non-local shear viscosity does not have a plateau. By using a recently proposed correction for the Green–Kubo formula that eliminates the plateau problem [Español et al., Phys. Rev. E 99, 022126 (2019)], we unambiguously obtain the actual non-local shear viscosity. The resulting Markovian equation, being local in time, is not valid for very short times. We observe that the Markovian equation with non-local viscosity gives excellent predictions for the correlation matrix from a time at which the correlation is around 80% of its initial value. A local in space approximation for the viscosity gives accurate results only after the correlation has decayed to 40% of its initial value.
