Set the solute and solvent selections

The solute and solvent are defined in ComplexMixtures as lists (vectors) of the indexes of the atoms of the system. The solute and solvent information is stored in the Selection structure. For example, if the solute is a molecule formed by the first 5 atoms of the system, it would be defined as:

indexes = [ 1, 2, 3, 4, 5 ]
solute = Selection(indexes,nmols=1)

The atom names can be also provided such that some of the output files contain more information on the atomic contributions. In this case the syntax is:

indexes = [ 1, 2, 3, 4, 5 ]
names = [ "H1", "H2", "H3", "H4", "C" ]
solute = Selection(indexes,names,nmols=1)

Using PDBTools

PDBTools is a package we developed to read and write PDB files, which provides a simple selection tool. It is installed as a dependency of ComplexMixtures. Given a PDB file of the simulated system, the solute can be defined as, for example,

using PDBTools
atoms = PDBTools.readPDB("system.pdb")
protein = PDBTools.select(atoms,"protein")
solute = Selection(protein,nmols=1)

If the solvent is, for instance, water, the indexes of the water molecules can be obtained with:

water = PDBTools.select(atoms,"water")
solvent = Selection(water,natomspermol=3)

or, alternatively, a more compact syntax can be used, for example:

water = PDBTools.select("system.pdb","resname TIP3P")
solvent = Selection(water,natomspermol=3)

or even providing just the names of the input file and selection, which will run PDBTools in background:

solvent = Selection("sytem.pdb","water",water,natomspermol=3)

Using VMD

VMD is a very popular and powerful package for visualization of simulations. It contains a very versatile library to read topologies and trajectory files, and a powerful selection syntax. We provide here a wrapper to VMD which allows using its capabilities.

For example, the solute can be defined with:

indexes, names = VMDselect("./system.gro","protein",vmd="/usr/bin/vmd")
solute = Selection(indexes,names,nmols=1)

The main advantage here is that all the file types that VMD supports are supported. But VMD needs to be installed and is run in background, and it takes a few seconds.