[lammps-users] sllod algorithm

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1

Hi Steve,

I have a question about the sllod algorithm implemented in the LAMMPS package (fix nvt/sllod). From the LAMMPS menu, non-equilibrium molecular dynamics or NEMD simulations could be realized by the fix nvt/sllod + fix deform commands.
I have run the NEMD simulation from the example files with ‘fix deform erate’, which could simulate the planar Couette flow and have a good agreement with my expectation.

However, when I simulated an oscillation shear on the fluid by ‘fix deform wiggle’, the temperature is not as the same as the temperature given in the fix nvt/sllod command. Even the velocity profile in the flow did not have a linear profile. I have checked some literature about the sllod algorithm. From the recent one (THE JOURNAL OF CHEMICAL PHYSICS 123, 114106 2005), the authors have studied both the sllod algorithm and p-sllod algorithm. The traditional sllod algorithm could be only valid for the planar Couette flow, but, the p-sllod algorithm could be used for arbitrary flows. Therefore, I have question that whether the sllod algorithm in the LAMMPS package can be used for the oscillation flow or planar extension flow?

Thanks.
Best,

2

I don't know the differences between sllod and p-sllod. But
the SLLOD in fix nvt sllod does have a term that applies
the "rate" of the deformation. That is a constant for
typical shear, but varies in time for osciallatory deformations.
We compute the correct time variation and use it in nvt/sllod.
However, and SLLOD or thermostatting is going to have
trouble keeping up with too rapid oscillations and maintaining
a linear profile.

Steve