# NEMD simulations Non-equilibrium molecular dynamics or NEMD simulations are typically used to measure a fluid\'s rheological properties such as viscosity. In LAMMPS, such simulations can be performed by first setting up a non-orthogonal simulation box (see the preceding Howto section). A shear strain can be applied to the simulation box at a desired strain rate by using the [fix deform](fix_deform) command. The [fix nvt/sllod](fix_nvt_sllod) command can be used to thermostat the sheared fluid and integrate the SLLOD equations of motion for the system. Fix nvt/sllod uses [compute temp/deform](compute_temp_deform) to compute a thermal temperature by subtracting out the streaming velocity of the shearing atoms. The velocity profile or other properties of the fluid can be monitored via the [fix ave/chunk](fix_ave_chunk) command. :::: note ::: title Note ::: A recent (2017) book by [(Daivis and Todd)](Daivis-nemd) discusses use of the SLLOD method and non-equilibrium MD (NEMD) thermostatting generally, for both simple and complex fluids, e.g. molecular systems. The latter can be tricky to do correctly. :::: As discussed in the previous section on non-orthogonal simulation boxes, the amount of tilt or skew that can be applied is limited by LAMMPS for computational efficiency to be 1/2 of the parallel box length. However, [fix deform](fix_deform) can continuously strain a box by an arbitrary amount. As discussed in the [fix deform](fix_deform) command, when the tilt value reaches a limit, the box is flipped to the opposite limit which is an equivalent tiling of periodic space. The strain rate can then continue to change as before. In a long NEMD simulation these box re-shaping events may occur many times. In a NEMD simulation, the \"remap\" option of [fix deform](fix_deform) should be set to \"remap v\", since that is what [fix nvt/sllod](fix_nvt_sllod) assumes to generate a velocity profile consistent with the applied shear strain rate. An alternative method for calculating viscosities is provided via the [fix viscosity](fix_viscosity) command. NEMD simulations can also be used to measure transport properties of a fluid through a pore or channel. Simulations of steady-state flow can be performed using the [fix flow/gauss](fix_flow_gauss) command. ------------------------------------------------------------------------ ::: {#Daivis-nemd} **(Daivis and Todd)** Daivis and Todd, Nonequilibrium Molecular Dynamics (book), Cambridge University Press, , (2017). :::