mirror of https://github.com/abinit/abinit.git
71 lines
3.6 KiB
Markdown
71 lines
3.6 KiB
Markdown
---
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description: How to compute phonon frequencies and modes, IR and Raman spectra, Born effective charges, IR reflectivity ...
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authors: MT
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---
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<!--- This is the source file for this topics. Can be edited. -->
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This page gives hints on how to compute phonon frequencies and modes, IR and Raman spectra, Born effective
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charges, IR reflectivity with the ABINIT package.
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## Introduction
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The computation of the second-order derivative of the total energy with
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respect to atomic displacements at an arbitrary wavevector, using
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[[topic:DFPT]], opens the possibility to compute the dynamical matrix at that
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wavevector, and hence, to compute the phonon eigenfrequency and
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eigendisplacements. When the wavevector is (0,0,0), usually denoted as the
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Gamma point, the combination of the atomic displacements and electric field
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type perturbations opens also the access to Born effective charges, electronic
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(for frequencies lower than the electronic band gap) dielectric constants, and
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then, to infra-red reflectivity of materials (in the infinite lifetime
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approximation). See [[cite:Gonze1997a]] and [[cite:Baroni2001]] for the presentation of the theory
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of DFPT, and [[cite:Gonze2024]] for the specificities for metals.
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In ABINIT, with one dataset for a fixed wavevector (see [[topic:q-points]]),
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one can compute all such second-order derivatives. ABINIT will already perform
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some post-processing treatment of the second-order derivatives (e.g.
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computation of the dynamical matrix, and corresponding eigenenergies and
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eigendisplacements), although the most extended post-processing treatment is
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provided by ANADDB. Thus, there is some overlap of the two executables, with
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some common input variables. Usually, the action of an input variable with the
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same name in the two executables is very similar, although there are some
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input variables that govern more options in ANADDB then in ABINIT, because of
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the previously mentioned difference in capabilities. In the database of input
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variables, the input variables related to ABINIT or ANADDB are clearly
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distinguished.
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The band-by-band decomposition of the Born effective charge tensors can be
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computed thanks to [[prtbbb]]. The related localization tensor (see
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[[cite:Veithen2002]] can also be computed.
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Phonon calculations are arbitrary q-points can be done under finite electric
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field ([[topic:Berry]]).
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It will be the easiest to discover the capabilities of these two executables
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through the [[tutorial:rf1]] of the tutorial.
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See [[topic:DFPT]] for the general information about DFPT, [[topic:q-points]]
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for the specification of q-points, and [[topic:PhononBands]] for the
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computation of full phonon bands.
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!!! important
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More than 1500 phonon band structures for insulators, computed with ABINIT, are now available
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on the [Materials Project web site](https://materialsproject.org), accompanied with derived
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thermodynamic quantities, Born effective charges, and dielectric tensor [[cite:Petretto2018a]].
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The DDB file can be downloaded automatically with |AbiPy| starting from the materials project
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identifier. For futher information, please consult the |DdbFileNb|.
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## Related Input Variables
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{{ related_variables }}
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## Selected Input Files
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{{ selected_input_files }}
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## Tutorials
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* [[tutorial:rf1|The tutorial Response-Function 1 (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.
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