
Copyright (C) 2003-2021 ABINIT group (XG)
This file is distributed under the terms of the
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or http://www.gnu.org/copyleft/gpl.txt .
For the initials of contributors, see ~abinit/doc/developers/contributors.txt .

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This README is in the Infos/Theory directory of the abinit package.
It has the aim to described the purpose and content of this "Theory"
directory.

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0. Introduction

There is a gap between the theory, as published in the scientific
papers, on which a code like ABINIT is build, and the documentation
that can be contained in the different routines. Indeed,
scientific papers cannot refer to specific routines to describe
where and how the formulas are implemented, while the information
that can be put in a routine cannot conveniently have the
mathematical format that is required to represent formulas.

The documentation
that you will find in this directory has precisly the aim to
bridge the gap. In the future, we hope to be able
to set up a system of hyperlinks that will connect
the routines, the theory files, and the scientific
papers.

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1. Classification of theory documents

First, we will describe two types of theory documents, that are
included in this directory :
- those of which the sources are available (e.g. a .tex file)
- those of which the sources are not available (e.g. a .pdf or .ps file)
The documents of the first type (.tex) are much more flexible, of course,
can have hyperlinks, and can be maintained.
Note that the compiled version of the .tex documents
can be prepared automatically by typing
make theory
in the ~abinit/doc directory.

There are other theory documents, not present in this directory.
Indeed, one does not have often the time to generate
a nice .tex file. Handwritten documents can still be a valuable
source of information about the code. Conference presentations
(e.g. in PowerPoint) can be also quite interesting. So,
it was decided to constitute a library of documents that would
also include some scanned hand-written documents and
ppt presentations.
Still, such documents can be very large, and the direct
inclusion within the ABINIT package is not be worth.
We consider these to form a third class of documents.
Such documents are available on the ABINIT community Web site :
http:// ...

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2. List of documents



2.1. .tex in the Theory directory

2.1.1. geometry.tex

ABINIT data structures and their theoretical justifications
Geometric considerations
Describes real space and reciprocal space conventions,
as well as symmetry operations

2.1.2. 1WF.tex

ABINIT data structures and their theoretical justifications
Representation and conversion of one wavefunction

2.1.3. set_WFs.tex

ABINIT data structures and their theoretical justifications
Representation and conversion of the set of wavefunctions

2.1.4. noncol.tex

Non colinear magnetism



2.2. Other documents in the Theory directory

2.2.1. gwa.pdf

The GW formalism : basic equations, and conventions

2.2.2. vanderbilt-anaddb-notes.pdf

Systematic treatment of crystal displacements, strains and
polarization. Discussion notes by D. Vanderbilt.

2.2.3. elasticity-oganov.pdf

Elastic constants, definitions and some discussion by A. Oganov.

2.2.4. elasticity-hamann_oganov_040611.pdf

A note written by Don Hamann to A. Oganov. More info should be provided.



2.3. Documents on the community Web site

2.3.1. The ppt presentations of the 1st ABINIT developer
workshop, Louvain-la-Neuve, November 6-8, 2002.
(see the index of the community Web site)

2.3.2. SpinOrbit.XG.pdf

Handwritten notes on the implementation of the spin-orbit
(by XGonze, scanned by Y. Suzukawa and M. Mikami)

2.3.3. SpinOrbit.FJ.pdf

Handwritten notes on the implementation of the spin-orbit,
(by FJollet, scanned by Y. Suzukawa and M. Mikami)
in French

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