Compute Phonon Linewidth and Thermal Conductivity

With the irreducible derivatives at second and third order computed with the methods described in the chapter Compute Irreducible Derivatives, we can predict the phonon linewidth and thermal conductivity using perturbation theory.

Phonon Linewidth

Here we continue the NaCl example from Compute Irreducible Derivatives.

First, we need to prepare a configuration file config.yml for the pm-conductivity command:

config.yml

structure: structure.yml
load_fi2: fi_order2.hdf5
load_fi3: fi_order3.hdf5
mesh: [11, 11, 11]
band:
  - ['0 0 0', '1/2 1/2 0']
  - ['-1/2 1/2 0', '0 0 0']
  - ['0 0 0', '1/2 1/2 1/2']
band_label:
  - $\Gamma$
  - X
  - $\Gamma$
  - L

where:

structure.yml contains structure of NaCl;
fi_order2.hdf5 is the HDF5 data file for the FourierInterpolation class at second order;
fi_order3.hdf5 is the HDF5 data file for the FourierInterpolation class at third order.

In this example, we use the FourierInterpolation object of a \(4\hat{\mathbf{1}}\) FTG (\(4 \times 4 \times 4\)) at second order and the FourierInterpolation object of a \(2\hat{\mathbf{1}}\) FTG (\(2 \times 2 \times 2\)) at third order. We interpolate the phonons and phonon interactions to the mesh of \(11\hat{\mathbf{1}}\) (\(11 \times 11 \times 11\)), and compute the linewidth along the K-path \(\Gamma \to X \to \Gamma \to L\).

Execute the following command the compute the phonon linewidth:

pm-conductivity --config config.yml --save-gamma

Thermal Conductivity

Using the same NaCl example, we can prepare a configuration file config.yml similar to the one above:

config.yml

structure: structure.yml
load_fi2: fi_order2.hdf5
load_fi3: fi_order3.hdf5
mesh: [11, 11, 11]

Execute the following command the compute the thermal conductivity using relaxation time approximation (RTA):

pm-conductivity --config config.yml --save-kappa --mode RTA