# compute_hnemd¶

This keyword is used to calculate the thermal conductivity using the homogeneous non-equilibrium molecular dynamics (HNEMD) method [Fan2019]. The results are written to the kappa.out output file.

## Syntax¶

compute_hnemd <output_interval> <Fe_x> <Fe_y> <Fe_z>


The first parameter is the output interval.

The next three parameters are the $$x$$, $$y$$, and $$z$$ components of the external driving force $$\boldsymbol{F}_e$$ in units of Å-1.

Usually, there should be only one nonzero component of $$\boldsymbol{F}_e$$. According to Eq. (8) of [Fan2019]:

• Using a nonzero $$x$$ component of $$\boldsymbol{F}_e$$, one can obtain the $$xx$$, $$yx$$ and $$zx$$ components of the thermal conductivity tensor.

• Using a nonzero $$y$$ component of $$\boldsymbol{F}_e$$, one can obtain the $$xy$$, $$yy$$ and $$zy$$ components of the thermal conductivity tensor.

• Using a nonzero $$z$$ component of $$\boldsymbol{F}_e$$, one can obtain the $$xz$$, $$yz$$ and $$zz$$ components of the thermal conductivity tensor.

## Examples¶

### Example 1¶

compute_hnemd 1000 0.00001 0 0


This means that

• you want to calculate the thermal conductivity using the HNEMD method;

• the thermal conductivity will be averaged and output every 1000 steps (the heat current is sampled for every step);

• the external driving force is along the $$x$$ direction and has a magnitude of $$10^{-5}$$ Å-1.

Note that one should control the temperature when using this keyword. Otherwise, the system will be heated up by the external driving force.

Important: For this purpose, the Nose-Hoover chain thermostat is recommended. The Langevin thermostat cannot be used for this purpose because it will affect the dynamics of the system.

### Example 2¶

compute_hnemd 1000 0 0.00001 0


This is similar to the above example, but the external driving force is applied along the $$y$$ direction.