The Anharmonic LAttice DYNamics (ALADYN) suite of codes and thermal properties of materials from first-principles data

We will present our work on the development of an anharmonic lattice dynamics model and its related codes.

The first code, FOrce Constants EXtraction (FOCEX) is able to extract from a force-displacement data anharmonic force constants up to rank 4. From them, a second code, THERMACOND, calculates the phonon dispersion and solves the Boltzmann equation to calculate the lattice THERMAl CONDuctivity beyond the relaxation time approximation.

Results on simple crystals such as FCC Ge and RbBr, and more complex structures such as the Pnma phase of GeSe, will be illustrated. A third code, ANharmonic FOrce MOlecular Dynamics (ANFOMOD) allows the user to use this force field to perform molecular dynamics and calculate for instance the thermal conductivity by using the Green-Kubo formula.

Finally, at high temperatures, lattice dynamical properties are described using the Self-COnsistent Phonon theory, SCOP. This code calculates, at a given temperature, the effective harmonic force constants, the related phonons and the equilibrium, eventually deformed, crystal structure and the relaxed atomic positions. It is therefore able to predict structural phase transitions in addition to thermal expansion.

These codes are now made available to the public under the GPL-3.0 licence, and can be freely downloaded from our github page.

https://github.com/KeivanS/Anharmonic-lattice-dynamics

The documentation and tutorials can be found at:

https://aladyn.readthedocs.io/en/latest/run.html