Effective harmonic models
Using hiPhive it is straightforward to generate effective harmonic models (EHMs) from molecular dynamics (MD) trajectories. These models enable one to describe one for example the temperature dependence of the phonon dispersion as well as derived quantities such as the harmonic free energy.
In this example we look construct EHMs from MD simulations for BCC tantalum. We use cutoffs of 6.0
With increasing temperature the ability of an EHM to map the forces present in the structure decreases as evident from the root-mean-square errors over the training set:
Temperature (K)
Train RMSE (meV/A)
300
41.3
1000
148.7
2000
315.2
The phonon dispersions obtained in this fashion are shown in the following figure.
Phonon dispersions for BCC Ta from a series of effective harmonic models generated from MD trajectories recorded at different temperatures.
Source code
MD structures are generated in
examples/advanced_topics/temperature_dependent_phonons/3a_run_fcp_md.py
Effective harmonic models are constructed in
examples/advanced_topics/temperature_dependent_phonons/3b_train_ehms.py
Phonon dispersion are plotted using
examples/advanced_topics/temperature_dependent_phonons/4b_plot_ehm_phonons.py