# The compute hnemd keyword

## Purpose

The compute_hnemd keyword is used to calculate the RTC (running thermal conductivity) using HNEMD method.

## Grammar

• This keyword has 4 parameters and looks like the following:
compute_hnemd output_interval Fe_x Fe_y Fe_z


The first parameter is the output interval. The next three parameters are the $x$, $y$, $z$ components of the external driving force $\vec{F}_{\rm e}$ in units of $Å^{-1}$.

## Examples

### Example 1

• An example of the keyword is:
compute_hnemd 1000 0.00001 0 0


This means that (1) you want to calculate the thermal conductivity using the HNEMD method; (2) the RTC will be averaged and output every 1000 steps (the heat current is sampled for every step); (3) the external driving force is along the $x$ direction and has a magnitude of $10^{-5} Å^{-1}$. The results will be written into a file named kappa.out in the same folder where you put your run.in file in. Note that one should control the temperature when using this keyword. Otherwise, the system will be heated up by the external driving force.