Examples from Foyer paper¶

Contained below are the toy examples from the Usage Examples section of the foyer paper. The source code selections are listed below on this page, there are Jupyter Notebooks where you can try these examples yourself. Note that these examples are meant to showcase the abilities of foyer through simple examples. If the user would like to examine more in-depth examples using foyer with mBuild, please refer to the tutorial repository.

Below is Listing 6 from the paper, a python script to fill a $$2x2x2 nm$$ box with 100 ethane molecules. The system is then atomtyped using the OPLS-AA forcefield. There are two approaches to the same problem detailed below in this listing, the first approach uses the forcefield_files function argument from mBuild to atomptype the system (using foyer under the hood). While the second approach creates a foyer Forcefield object, which then calls its apply function, operating on the mBuild Compound to return the properly atomtyped structure. Note that in all instances when using foyer, the chemical system of interest is converted into a ParmEd Structure. Even the mBuild Compounds, when calling the save routine, are converted into a ParmEd Structure before foyer can atomtype them. The object returned by foyer after the atomtypes have been applied are ParmEd Structures. This is subject to change in later iterations of foyer.

Homogeneous fluid¶

import mbuild as mb
from mbuild.lib.molecules import Ethane
from foyer.examples.utils import example_file_path
from foyer import Forcefield

""" Applying a force field while saving from mBuild """
# Create the chemical topology
ethane_fluid = mb.fill_box(compound=Ethane(), n_compounds=100, box=[2, 2, 2])
# Apply and save the topology
ethane_fluid.save("ethane-box.top", forcefield_files=example_file_path("oplsaa_alkane.xml"))
ethane_fluid.save("ethane-box.gro")

""" Applying a force field directly with foyer """
# Create the chemical topology
ethane_fluid = mb.fill_box(compound=Ethane(), n_compounds=100, box=[2, 2, 2])
opls_alkane = Forcefield(forcefield_files=example_file_path("oplsaa_alkane.xml"))
# Apply the forcefield to atom-type
ethane_fluid = opls_alkane.apply(ethane_fluid)
# Save the atom-typed system
ethane_fluid.save("ethane-box.top", overwrite=True)
ethane_fluid.save("ethane-box.gro", overwrite=True)

Fluid on silica substrate¶

The other example listing from the text showcases the ability to create two separate chemical topologies and applying different forcefield files to each. The two parameterized systems that are generated are then combined into a single ParmEd Structure and saved to disk.

from foyer import Forcefield
from foyer.examples.utils import example_file_path
import mbuild as mb
from mbuild.examples import Ethane
from mbuild.lib.atoms import H
from mbuild.lib.bulk_materials import AmorphousSilicaBulk
from mbuild.lib.recipes import SilicaInterface
from mbuild.lib.recipes import Monolayer

# Create a silica substrate, capping surface oxygens with hydrogen
silica=SilicaInterface(bulk_silica=AmorphousSilicaBulk())
silica_substrate=Monolayer(surface=silica,chains=H(),guest_port_name="up")
# Determine the box dimensions dictated by the silica substrate
box=mb.Box(mins=[0, 0,max(silica.xyz[:,2])],maxs=silica.periodicity+ [0, 0, 4])
# Fill the box with ethane
ethane_fluid=mb.fill_box(compound=Ethane(),n_compounds=200,box=box)