mirror of https://github.com/abinit/abinit.git
50 lines
2.3 KiB
Markdown
50 lines
2.3 KiB
Markdown
---
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description: How to perform a Tdep calculation
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authors: FBottin, JBouchet
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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 perform thermodynamic, elastic and transport properties calculations including explicit temperature effects with the ABINIT package.
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* User guide: [[pdf:aTDEP_Guide|aTDEP_Guide]]
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* Theory: [[pdf:aTDEP_Paper|aTDEP_Paper]] corresponding to the article [[cite:Bottin2020]]
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## Introduction
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The Temperature Dependent Effective Potential (TDEP) method
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has been developped by O. Hellman *et al.* [[cite:Hellman2011]],
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[[cite:Hellman2013]], [[cite:Hellman2013a]] in 2011 and the |aTDEP| implementation
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in ABINIT has been performed and used for the first time in 2015 by
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J. Bouchet and F. Bottin [[cite:Bouchet2015]], [[cite:Bouchet2017]].
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The capture of thermal effects in solid state physic is a long standing
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issue and several stand-alone or post-process computational codes are
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available. Using different theoretical frameworks, they propose to provide
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some thermodynamic quantities involving the so called anharmonic effects.
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|aTDEP| calculation can produce almost all the temperature-dependent
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thermodynamic quantities you want, from a single *ab initio*
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molecular dynamic (AIMD) trajectory and by means of a Graphical User
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Interface (GUI) very easy to use ([[https://github.com/abinit/abiout|AGATE]]).
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The original TDEP method [[cite:Hellman2011]] is implemented in ABINIT.
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In particular, various algorithms can be used to obtain the Interatomic Force Constants (IFC).
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The 2nd-order (and soon 3rd-order) IFCs are produced self-consistently using a least-square
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method fitting the AIMD forces on a model Hamiltonian function of the displacements.
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Numerous thermodynamic quantities can be computed starting from the
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2nd order IFCs. The 1st one is the phonon spectra, from which a large
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number of other quantities flow : internal energy, entropy, free energy, specific heat...
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The elastic constants and other usual elastic moduli (the bulk,
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shear and Young moduli) can be also produced at this level. Using the 3rd
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order IFCs, we could extract the Gruneisen parameter, the thermal
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expansion, the sound velocities... and in particular, how to take into account
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the anisotropy of the system within.
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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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