WIP: Backbone of a tutorial

src/Advanced.rst

@@ -0,0 +1,14 @@
+Advanced Section
+================
+
+These pages provide introduction tutorials for people familiar with molecular
+simulation who want to "get things done" in LAMMPS
+
+..
+   From G.Clavier:
+   WIP: This section might use or refer to more of the material in the How-to
+   section of the manual
+
+.. toctree::
+   :maxdepth: 1
+

src/Beginner.rst

@@ -0,0 +1,15 @@
+Beginner Section
+================
+
+These pages provide introduction tutorials for people unfamiliar with molecular
+simulation softwares and practice.
+
+.. toctree::
+   :maxdepth: 1
+
+   file_format
+   setting_up_simulations
+   running_and_post_processing
+   variables_computes_fixes
+   averages_and_on_the_fly_computation
+   visualising_trajectories

src/Confirmed.rst

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+Confirmed Section
+=================
+
+These pages provide introduction tutorials for people who have a good knowledge
+of LAMMPS and want to go deeper in setting complicated simulation environment
+or Python coupling.
+
+.. 
+   From G.Clavier:
+   WIP: This section might get technical but given the current state of LAMMPS
+   questions in the forum, this is not the most pressing matter IMO.
+
+.. toctree::
+   :maxdepth: 1
+

src/Learning_MD.rst

@@ -5,3 +5,54 @@ Learning Molecular Dynamics with LAMMPS (version |version|)
 LAMMPS is a classical molecular dynamics simulation code focusing on
 materials modeling.
 
+Quoting the first paragraph of the overview section of the manual_:
+
+  LAMMPS is a classical molecular dynamics (MD) code that models ensembles of
+  particles in a liquid, solid, or gaseous state. It can model atomic,
+  polymeric, biological, solid-state (metals, ceramics, oxides), granular,
+  coarse-grained, or macroscopic systems using a variety of interatomic
+  potentials (force fields) and boundary conditions. It can model 2d or 3d
+  systems with sizes ranging from only a few particles up to billions.
+
+In this tutorials, you will find step-by-step guides that aim at giving you
+some fundamental comprehension of the code, basic input/output manipulation and
+visualization of your simulation in order to give you some autonomy in the use
+of the LAMMPS software. This does not replace proper teaching of statistical
+mechanics and direct adivising from skilled users close to you and your work
+environment but should give you some basic understanding to start your learning
+of molecular simulation.
+
+These tutorials assume you are familiar with text file manipulation, basic
+command-line use and your computer environment. They also assume you already
+have LAMMPS executable installed. If not, contact your IT departement or follow
+the `installation guide <https://docs.lammps.org/Install.html>`_ from the
+manual. If necessary, also see `how to run LAMMPS executable dedicated
+section. <https://docs.lammps.org/Run_head.html>`_ LAMMPS usage is generally
+easier on UNIX like systems (Linux distributions, macOS) so most examples will
+assume this type of environment. On Windows systems, you can set-up WSL to be
+in an equivalent environment.
+
+As for now the tutorial is organised in three main sections, mainly:
+
+1. Beginner: for people who have no experience whatsoever with molecular
+   simulation codes
+2. Advanced: for people with some familiarity with molecular simulation that
+   want to know how to do more refined things in LAMMPS.
+3. Confirmed: Detailed discussions on the howto examples from the manual.
+
+****************
+Table of content
+****************
+
+.. toctree::
+   :maxdepth: 2
+   :numbered: 2
+   :caption: Table of content
+   :name: tutorialtoc
+   :includehidden:
+
+   Beginner
+   Advanced
+   Confirmed
+
+.. _manual: https://docs.lammps.org

src/averages_and_on_the_fly_computation.rst

@@ -0,0 +1,4 @@
+=====================================================
+Using averages and computing values during simulation
+=====================================================
+

src/file_format.rst

@@ -0,0 +1,189 @@
+================================
+Introduction to the file formats
+================================
+
+LAMMPS internally keeps track of the evolution of atomistic systems. Such a
+system is described as a `simulation box` containing an ensemble of particles
+interacting with one another according to set of rules, and each with their own
+position, velocities etc.
+
+In this section, you will learn how to create a very simple simulation box
+using LAMMPS built-in tools.
+
+Running a minimal LAMMPS input
+------------------------------
+
+In an empty directory, open a text file and copy the following text inside:
+
+.. code-block:: LAMMPS
+
+   lattice sc 1.
+   region box block 0 5 0 5 0 5
+   create_box 1 box
+   create_atoms 1 box
+
+   mass 1 1
+
+   write_data data.lmp
+   write_dump all atom dump.lammpstrj
+
+Let's save the file with the name `in.lmp`. Now in the command-line you can
+run the following command to execute LAMMPS with this input:
+
+.. code-block:: bash
+
+   lmp -i in.lmp
+
+You should see a bunch of line appear in your screen. The first one should start
+with `LAMMPS` followed by a parentheses with the specification of the version
+of the code you are using. The last line should read something like
+`Total wall time: 00:00:00`. If you've never executed LAMMPS before,
+congratulation! This is maybe your first sucessful (very simple) simulation!
+
+You will also notice that two file appeared in the directory: `data.lmp` and
+`dump.lammpstrj`. Let's start by opening the first one.
+
+Data file format
+****************
+
+The first file of the two is usually referred to as a `data file`. Its format
+is rather strict and you can see that there are general information at the
+top of the file and several sections starting with a capitalized word, a blank
+line and some numbers. Let's slowly go through all of this.
+
+The first part of the file is called `the header`. The first line of the file
+is always a comment that LAMMPS does not read but which can contain
+informations on the way the file was generated. Here we see the LAMMPS version
+and some more information like timestep and units. The following lines contain
+the number of `atoms` (125), the number of `atom types` (1) and three lines
+containing `xlo xhi` like indications. This header is simple, but generally,
+headers can contain much more informations. The first two lines are explicit,
+you define a system with 125 atoms all of which have the same caracteristics.
+The last three lines define the volume in which these atoms are contained. It
+is a box with edge coordinates starting at 0 and ending at 5 in every direction
+(x, y and z).
+
+From here starts the body of the file. The order of the sections is not important
+but all of them must come in the format:
+
+.. code-block:: LAMMPS
+
+   Section name # Capitalized, correctly spelled
+   # blank line
+   Section input # Number of line and format depend on the section.
+
+The first section you should see is the `Masses` section. In LAMMPS, masses are
+assigned to atom types so you only have one line here. All types have their own
+masses but several types can have the same mass. Types are LAMMPS way to refer
+to properties of particles that are *the same* for all particles of *the same
+type*. They are also used to determine how particles interact with one another.
+Types are not always binded to chemical species and you will see in further
+tutorials how it can be convenient to define different types for similar atoms.
+
+The `Atoms` section contains 125 lines, one per atom. The number on each line
+are ordered and are for each particle:
+* The particle ID which LAMMPS uses to refer to that particle internally
+* The type of the particle
+* The x, y and z coordinates in absolute distance value
+* The xflag, yflag and zflag values, which you can put aside for now
+
+Below you can also see the `Velocities` section which also contains 125 lines.
+Each lines gives the particle ID followed by the instantaneous velocities of
+the particles along the x, y and z axis in that order. The particle ID refers
+to the same ID as in the `Atoms` section.
+
+The format and meaning of the number in the `Atoms` and `Velocities` sections
+will depend on the `atom_style` the code is told to use. In most recents
+versions of LAMMPS, writing a data file with `write_data` will append a comment
+next to the `Atoms` section name (here `# atomic`). This helps human readers to
+know the meaning of the different number. Some formats can include more
+information like a molecule tag, particles' charges, particles' spins or
+orientation etc. For the velocities, some `atom_style` can require keeping
+track of angular momentum, angular velocities etc. You'll find a detailed
+description of each format in the `read_data section of the manual`_.
+
+As a first takeaway, remember that `data files` contain detailed informations
+on a simulation system at a given time. They are more convenient for input and
+output. Several simulation softwares allow you to export files as LAMMPS
+`data files` and take them as input. But data format are not straightforward to
+use for analyses: they are heavy and may contain useless informations. This is
+what the dump file format is for.
+
+Dump file format
+****************
+
+Following the previous sections, open the `dump.lammpstrj` file that should
+have appeared in your directory. This is a `dump file` containing a single
+`snapshot` You should see something like this:
+
+.. code-block:: LAMMPS
+
+  ITEM: TIMESTEP
+  0
+  ITEM: NUMBER OF ATOMS
+  125
+  ITEM: BOX BOUNDS pp pp pp
+  0.0000000000000000e+00 5.0000000000000000e+00
+  0.0000000000000000e+00 5.0000000000000000e+00
+  0.0000000000000000e+00 5.0000000000000000e+00
+  ITEM: ATOMS id type xs ys zs
+  1 1 0 0 0
+  2 1 0.2 0 0
+  3 1 0.4 0 0
+  4 1 0.6 0 0
+  5 1 0.8 0 0
+  ...
+
+The format is more simple compared to the data file. Each section is labeled
+with a header directly followed by the data we wanted to dump. Here we used the
+basic atom dump_style so we only have atoms' id, types and scaled coordinates
+(that is coordinates divided by box length in each dimension).
+
+You can compare the informations with the one you got from the `data file` and
+see that for now we have the same information in both files, with some
+exceptions (total number of types, masses and the velocities). Getting only the
+scaled coordinates of the atoms is a bit limited but fortunately, we can get
+much more.
+
+In your `in.lmp` file, replace the `write_dump` line with the following:
+
+.. code-block:: LAMMPS
+
+   write_dump all custom dump.lammpstrj id type x y z vx vy vz
+
+Save the file, and run the code as previously:
+
+.. code-block:: bash
+
+   lmp -i in.lmp
+
+Now the `dump.lammpstrj` file should have changed to the following:
+
+.. code-block:: LAMMPS
+
+  ITEM: TIMESTEP
+  0
+  ITEM: NUMBER OF ATOMS
+  125
+  ITEM: BOX BOUNDS pp pp pp
+  0.0000000000000000e+00 5.0000000000000000e+00
+  0.0000000000000000e+00 5.0000000000000000e+00
+  0.0000000000000000e+00 5.0000000000000000e+00
+  ITEM: ATOMS id type x y z vx vy vz
+  1 1 0 0 0 0 0 0
+  2 1 1 0 0 0 0 0
+  3 1 2 0 0 0 0 0
+  4 1 3 0 0 0 0 0
+  5 1 4 0 0 0 0 0
+  ...
+
+You now have different information in your dump file. The `custom` format allows
+you to write every properties of each atoms to the file. There are a series of
+keywords that you can use depending on the `atom_style` and values that you
+can also calculate through the use of LAMMPS computes and variables. More on
+that in later tutorials.
+
+For now on we haven't done much with our atoms. Let's see how to run an actual
+simulation.
+
+.. _read_data section of the manual: https://docs.lammps.org/read_data.html

src/running_and_post_processing.rst

@@ -0,0 +1,4 @@
+===========================
+Running and post-processing
+===========================
+