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| How to compute phonon frequencies and modes, IR and Raman spectra, Born effective charges, IR reflectivity ... | MT |
This page gives hints on how to compute phonon frequencies and modes, IR and Raman spectra, Born effective charges, IR reflectivity with the ABINIT package.
Introduction
The computation of the second-order derivative of the total energy with respect to atomic displacements at an arbitrary wavevector, using topic:DFPT, opens the possibility to compute the dynamical matrix at that wavevector, and hence, to compute the phonon eigenfrequency and eigendisplacements. When the wavevector is (0,0,0), usually denoted as the Gamma point, the combination of the atomic displacements and electric field type perturbations opens also the access to Born effective charges, electronic (for frequencies lower than the electronic band gap) dielectric constants, and then, to infra-red reflectivity of materials (in the infinite lifetime approximation). See cite:Gonze1997a and cite:Baroni2001 for the presentation of the theory of DFPT, and cite:Gonze2024 for the specificities for metals.
In ABINIT, with one dataset for a fixed wavevector (see topic:q-points), one can compute all such second-order derivatives. ABINIT will already perform some post-processing treatment of the second-order derivatives (e.g. computation of the dynamical matrix, and corresponding eigenenergies and eigendisplacements), although the most extended post-processing treatment is provided by ANADDB. Thus, there is some overlap of the two executables, with some common input variables. Usually, the action of an input variable with the same name in the two executables is very similar, although there are some input variables that govern more options in ANADDB then in ABINIT, because of the previously mentioned difference in capabilities. In the database of input variables, the input variables related to ABINIT or ANADDB are clearly distinguished.
The band-by-band decomposition of the Born effective charge tensors can be computed thanks to prtbbb. The related localization tensor (see cite:Veithen2002 can also be computed.
Phonon calculations are arbitrary q-points can be done under finite electric field (topic:Berry).
It will be the easiest to discover the capabilities of these two executables through the tutorial:rf1 of the tutorial.
See topic:DFPT for the general information about DFPT, topic:q-points for the specification of q-points, and topic:PhononBands for the computation of full phonon bands.
!!! important
More than 1500 phonon band structures for insulators, computed with ABINIT, are now available
on the [Materials Project web site](https://materialsproject.org), accompanied with derived
thermodynamic quantities, Born effective charges, and dielectric tensor [[cite:Petretto2018a]].
The DDB file can be downloaded automatically with |AbiPy| starting from the materials project
identifier. For futher information, please consult the |DdbFileNb|.
Related Input Variables
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Selected Input Files
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Tutorials
- tutorial:rf1 presents the basics of DFPT calculations within ABINIT. The example given is the study of dynamical and dielectric properties of AlAs (an insulator): phonons at Gamma, dielectric constant, Born effective charges, LO-TO splitting, phonons in the whole Brillouin zone. The creation of the "Derivative Data Base" (DDB) is presented.