mirror of https://github.com/abinit/abinit.git
61 lines
2.6 KiB
Markdown
61 lines
2.6 KiB
Markdown
---
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description: How to compute linear and non-linear optical properties in the independent-particle approximation
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authors: SS, XG, YG
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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 linear and non-linear optical properties
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in the independent-particle approximation with the Abinit package.
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## Introduction
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Optical and non-linear optical properties can be computed with different
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levels of approximation.
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The simplest (and fastest) approach relies on the independent-particle
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approximation (IPA): the electrons are supposed independent of each other when
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reacting to the optical perturbation (even if the initial computation of the
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band structure includes interactions in a mean-field sense, like with DFT).
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This approximation is also referred to as a "Sum-Over-States" approach (SOS).
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This neglects all electron-hole interaction (so no excitonic effects), but
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might provide meaningful results in many case, sometimes even quantitatively.
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A first problem is linked with the erroneous band gap of the material, but
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this can be corrected by a scissor approximation, see [[scissor@optic]].
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In Abinit one can either work in the IPA (see below), or take into account the
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excitonic effects, see [[topic:BSE]].
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In the Abinit package, there are two different utilities to compute optical
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responses in the independent-particle approximation: [[help:optic]] and
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conducti [[cite:Mazevet2010]]. They have been developed independently of each other, and thus
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overlap significantly. The first one computes the linear and non-
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linear optical properties as a function of the frequency. It provides the
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optical dielectric tensor, the second-harmonic generation (SHG) as well as the
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optical rectification tensor (or electro-optic tensor) - without the
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contribution from the nuclear displacements. For the further inclusion of the
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contribution from nuclear displacements, see [[topic:nonlinear]].
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The second utility "conducti" has more capabilities but only at the linear level,
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providing the electronic conductivity, dielectric tensor, index of refraction,
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reflectivity, absorption, the thermal conductivity, and the thermopower
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(electron transport, high temperature, Kubo-Greenwood formalism), the real as well
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as imaginary parts.
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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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* See [[tutorial:optic|The tutorial on Optic]], the utility that allows to obtain the
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frequency dependent linear optical dielectric function and the frequency
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dependent second order nonlinear optical susceptibility, in the simple
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"Sum-Over-States" approximation.
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