Msys is a library for inspecting and manipulating chemical structures of the sort used in molecular simulations. Its main features include:

• Efficient representation of chemical systems and forcefields;

• A powerful atom selection language;

• Command line tools for scripting common tasks;

• C++ and Python interfaces.

Msys currently supports Python 3.6+.

Building Msys

To build Msys, you'll need at a minimum the following:

• A recent gcc compiler supporting C++11; gcc 5.2 or later should work.

• Boost libraries (https://www.boost.org) version 1.67 or later. Earlier versions may also work, but a change in the naming convention for the boost python libraries means you'll have an easier time if you can use 1.67. Besides the boost headers, msys uses the following boost libraries: filesystem, system, and iostreams. In addition, you'll almost certainly want to compile the msys python bindings, which use the pybind11 library (https://pybind11.readthedocs.io/en/stable/).

• The numpy (http://www.numpy.org) headers for each python version you want to support.

• Scons (https://scons.org), a build tool, available through pip install.

• sconsutils, a set of extensions to Scons. A copy has been placed in /external; add it to your PYTHONPATH before building with:

  export PYTHONPATH=external:$PYTHONPATH

Msys can make use of several optional libraries when they are explicitly enabled during compilation. These libraries are:

• lpsolve (https://sourceforge.net/projects/lpsolve/), needed for bond order and formal charge assigment.

• The InChI library (https://www.inchi-trust.org/downloads/) version 1.05.

Once you've obtained the necessary dependencies, build msys by running the scons tool at the command line:

scons -j4

This should build the msys libraries in a build subdirectory, placing scripts in build/bin and python modules in build/lib/python. If anything fails at this point, check that you have a recent enough compiler, and that the boost headers are installed in a location that is normally searched by the compiler (e.g. /usr/include or /usr/local/include).

At this point, the scripts in build/bin aren't really usable since no python bindings have been built. In order to build the python bindings for msys, run the scons tool again, specifying which python version or versions you want to build for. For example, to build for Python 3.7, assuming python3.7 is in your shell's PATH, run::

scons -j4 PYTHONVER=37

Assuming that works, you should be able to use all the scripts and programs in build/bin. Try it with

./build/bin/dms-info tests/files/two.mae

You should get a summary of the structure and forcefield information contained in the file.

The scripts and python extensions you've just built are usable from the root of the msys source directory, but need to be installed before they can be used from other locations. To install what you've built, specify install on the scons command line and add a PREFIX argument::

scons -j4 PYTHONVER=37 install PREFIX=$HOME/local
export PATH=$HOME/local/bin:$PATH
export PYTHONPATH=$HOME/local/lib/python:$PYTHONPATH

You should now be able to run the msys scripts and use the python interface.

Building with InChI Support

In order to build msys with support for generation of InChI strings, download version 1.05 of the InChI source files from here: https://www.inchi-trust.org/downloads/. The name of the file will be INCHI-1-SRC.zip. Unzip the file in external/inchi/, which should create a directory named INCHI-1-SRC in that location. If you now build msys with the MSYS_WITH_INCHI option, msys will build the inchi library from source files and link against it:

scons -j4 PYTHONVER=37 -D MSYS_WITH_INCHI=1

Assuming the build was successful, you can generate an InChI string in msys using the python interface:

PYTHONPATH=build/lib/python:$PYTHONPATH python

>>> import msys
>>> mol = msys.Load("tests/files/stereo.sdf")
>>> print(msys.InChI(mol).string)
InChI=1/2C2H2F2/c2*3-1-2-4/h2*1-2H/b2-1+;2-1-

Building with Lpsolve Support

Msys uses lpsolve in a module that determines chemically reasonable bond orders and formal charges in systems for which this information is absent, but all atoms are present. The bond order assigner is reachable from python through the msys.AssignBondOrderAndFormalCharge function, as well as through the dms-select command line tool.

To build msys with lpsolve support, download lp_solve_5.5.2.5_source.tar.gz from here:

https://sourceforge.net/projects/lpsolve/files/lpsolve/5.5.2.5/

Then unpack it into the external/lpsolve directory, creating subdirectory named lp_solve_5.5 containing the lpsolve source files. Building msys with the MSYS_WITH_LPSOLVE option should now result in the lpsolve library being built from source and linked into msys, and bond order assignment should be enabled:

scons -j4 PYTHONVER=37 -D MSYS_WITH_INCHI=1 -D MSYS_WITH_LPSOLVE=1

To test that bond order assignment is available, run the following command:

./build/bin/dms-select tests/files/jandor-bad.sdf -o assign.sdf -A

The last few lines of assign.sdf should specify formal charges on two atoms:

...
M  CHG  1  30   1
M  CHG  1  31  -1
...