This is a simple example of how Bayesian atom type sampling using reversible-jump Markov chain Monte Carlo (RJMCMC) [1] over SMARTS types might work.
All tools for implementation of the SMIRNOFF in OpenMM have been moved to the openforcefield repository
examples/- some toy examples - look here to get startedsmarty/- simple toolkit illustrating the use of RJMCMC to sample over SMARTS-specified atom types and SMIRKS-specified bonded and non-bonded parameter types.devtools/- continuous integration and packaging scripts and utilitiesoe_license.txt.enc- encrypted OpenEye license for continuous integration testing.travis.yml- travis-ci continuous integration fileutilities/- some utility functionality relating to the project, specifically testing the speed of ChemicalEnvironments for sampling in SMIRKY.
Install miniconda first. On osx with bash, this is:
wget https://repo.continuum.io/miniconda/Miniconda2-latest-MacOSX-x86_64.sh
bash Miniconda2-latest-MacOSX-x86_64.sh -b -p $HOME/miniconda
export PATH="$HOME/miniconda/bin:${PATH}""
You must first install the OpenEye toolkit:
pip install -i https://pypi.anaconda.org/OpenEye/simple OpenEye-toolkits
You can then use conda to install smarty:
conda config --add channels omnia
conda install -c omnia smarty
Install smarty from the smarty/ directory with:
pip install .If you modify the smarty source code (rather than the examples), reinstall with
pip install . --upgradeCheck out the example in examples/smarty/:
Atom types are specified by SMARTS matches with corresponding parameter names.
First, we start with a number of initial "base types" which are essentially indestructible (often generic) atom types, specified in atomtypes/basetypes.smarts:
% atom types
[#1] hydrogen
[#6] carbon
[#7] nitrogen
[#8] oxygen
[#9] fluorine
[#15] phosphorous
[#16] sulfur
[#17] chlorine
[#35] bromine
[#53] iodine
Note that lines beginning with % are comment lines.
We also specify a number of starting types, "initial types" which can be the same or different from the base types. These follow the same format, and atomtypes/basetypes.smarts can be reused unless alternate behavior is desired (such as starting from more sophisticated initial types).
We have two sampler options for SMARTY which differ in how focused the sampling is. The original sampler samples over all elements/patterns at once, whereas the elemental sampler focuses on sampling only one specific element. The principle of sampling is the same; the only change is in which elements we sample over. To sample only over a single element, such as oxygen, for example, we use the elemental sampler to focus on that element.
There are two options for how to change SMARTS patterns when creating new atom types.
One is using combinatorial decorators (default) and the other is using simple decorators (--decoratorbehavior=simple-decorators). However, it should be noted that we have found the simple decorators insufficient at distinguishing atomtypes even for the most simple sets of molecules.
Combinatorial Decorators
The first option (combinatorial-decorator) attempt to create the new atomtype adding an Alpha or Beta substituent to a basetype or an atomtype.
This decorators are different from the simple-decorator option and do not have atom types or bond information on it.
The new decorators are listed in AlkEthOH/atomtypes/new-decorators.smarts and parm@frosst/atomtypes/new-decorators.smarts:
% total connectivity
X1 connections-1
X2 connections-2
X3 connections-3
X4 connections-4
% total-h-count
H0 total-h-count-0
H1 total-h-count-1
H2 total-h-count-2
H3 total-h-count-3
% formal charge
+0 neutral
+1 cationic+1
-1 anionic-1
% aromatic/aliphatic
a aromatic
A aliphatic
Each decorator has a corresponding string token (no spaces allowed!) that is used to create human-readable versions of the corresponding atom types.
For example, we may find the atom type [#6]&H3 which is carbon total-h-count-3 for a C atom bonded to three hydrogens.
Simple Decorators
The second option (simple-decorators) attempts to split off a new atom type from a parent atom type by combining (via an "and" operator, &) the parent atom type with a "decorator".
The decorators are listed in AlkEthOH/atomtypes/decorators.smarts or parm@frosst/atomtypes/decorators.smarts:
% bond order
$([*]=[*]) double-bonded
$([*]#[*]) triple-bonded
$([*]:[*]) aromatic-bonded
% bonded to atoms
$(*~[#1]) hydrogen-adjacent
$(*~[#6]) carbon-adjacent
$(*~[#7]) nitrogen-adjacent
$(*~[#8]) oxygen-adjacent
$(*~[#9]) fluorine-adjacent
$(*~[#15]) phosphorous-adjacent
$(*~[#16]) sulfur-adjacent
$(*~[#17]) chlorine-adjacent
$(*~[#35]) bromine-adjacent
$(*~[#53]) iodine-adjacent
% degree
D1 degree-1
D2 degree-2
D3 degree-3
D4 degree-4
D5 degree-5
D6 degree-6
% valence
v1 valence-1
v2 valence-2
v3 valence-3
v4 valence-4
v5 valence-5
v6 valence-6
% total-h-count
H1 total-h-count-1
H2 total-h-count-2
H3 total-h-count-3
% aromatic/aliphatic
a atomatic
A aliphatic
This option also has the corresponding string tokens.
Newly proposed atom types are added to the end of the list. After a new atom type is proposed, all molecules are reparameterized using the new set of atom types. Atom type matching proceeds by trying to see if each SMARTS match can be applied working from top to bottom of the list. This means the atom type list is hierarchical, with more general types appearing at the top of the list and more specific subtypes appearing at the bottom.
If a proposed type matches zero atoms, the RJMCMC move is rejected.
Currently, the acceptance criteria does not include the full Metropolis-Hastings acceptance criteria that would include the reverse probability. This needs to be added in.
The input option --element allows a user to specify which atoms types to sample based on atomic number. The default input is 0 (corresponding to no specified atomic number) and will attempt to match all atom types. If an element number is given (i.e. --element=1 for hydrogen) only atoms with that atomic number are considered. Specifying an element number does not affect any other smarty behavior.
Finally, here is a complete list of input options for smarty. Under usage all bracketed parameters are optional.
Usage: Sample over atom types, optionally attempting to match atom types in a reference typed set of molecules.
usage: smarty --basetypes smartsfile --initialtypes smartsfile
--decorators smartsfile --molecules molfile
[--element atomicnumber --substitutions smartsfile --reference molfile
--decoratorbehavior combinatorial-decorators/simple-decorators
--iterations niterations --temperature temperature --trajectory trajectorfile
--plot plotfile]
example:
python smarty --basetypes=atomtypes/basetypes.smarts --initialtypes=atomtypes/initialtypes.smarts \
--decorators=atomtypes/decorators.smarts --substitutions=atomtypes/substitutions.smarts \
--molecules=molecules/zinc-subset-tripos.mol2.gz --reference=molecules/zinc-subset-parm@frosst.mol2.gz \
--iterations 1000 --temperature=0.1
Options:
--version show program's version number and exit
-h, --help show this help message and exit
-e ELEMENT, --element=ELEMENT
By default the element value is 0 corresponding to
sampling all atomtypes. If another atomic number is
specified only atoms with that atomic number are
sampled (i.e. --element=8 will only sample atomtypes
for oxygen atoms).
-b BASETYPES, --basetypes=BASETYPES
Filename defining base or generic atom types as SMARTS
atom matches; these are indestructible and normally
are elemental atom types.
-f BASETYPES, --initialtypes=BASETYPES
Filename defining initial (first) atom types as SMARTS
atom matches.
-d DECORATORS, --decorators=DECORATORS
Filename defining decorator atom types as SMARTS atom
matches.
-s SUBSTITUTIONS, --substitutions=SUBSTITUTIONS
Filename defining substitution definitions for SMARTS
atom matches (OPTIONAL).
-r REFMOL, --reference=REFMOL
Reference typed molecules for computing likelihood
(must match same molecule and atom ordering in
molecules file) (OPTIONAL).
-m MOLECULES, --molecules=MOLECULES
Small molecule set (in any OpenEye compatible file
format) containing 'dG(exp)' fields with experimental
hydration free energies.
-i ITERATIONS, --iterations=ITERATIONS
MCMC iterations.
-t TEMPERATURE, --temperature=TEMPERATURE
Effective temperature for Monte Carlo acceptance,
indicating fractional tolerance of mismatched atoms
(default: 0.1). If 0 is specified, will behave in a
greedy manner.
-l TRAJECTORY_FILE, --trajectory=TRAJECTORY_FILE
Name for trajectory file output, trajectory saves only
changes to the list of 'atomtypes' for each iteration.
If the file already exists, it is overwritten.
-p PLOT_FILE, --plot=PLOT_FILE
Name for output file of a plot of the score versus
time. If not specified, none will be written. If
provided, needs to use a file extension suitable for
matplotlib/pylab. Currently requires a trajectory file
to be written using -l or --trajectory.
-x DECORATOR_BEHAVIOR, --decoratorbehavior=DECORATOR_BEHAVIOR
Choose between simple-decorators or combinatorial-
decorators (default = combinatorial-decorators).
Check out examples in examples/smirky/:
This tool can sample any chemical environment type relevant to SMIRNOFFs, that is atoms, bonds, angles, and proper and improper torsions, one at a time Scoring is analous to smarty (explained above), but uses a SMIRNOFF with existing parameters as a reference insteady of atomtyped molecules.
Input for this tool can require up to four different file types
- MOLECULES - any file that are readable in openeye, mol2, sdf, oeb, etc.
- ODDSFILES - File with the form "smarts odds" for the different decorator or bond options
- SMARTS - .smarts file type with the form "smarts/smirks label/typename"
- REFERENCE - a SMIRNOFF file with reference atoms, bonts, angles, torsions, and impropers
Usage: Sample over fragment types (atoms, bonds, angles, torsions, or impropers)
optionally attempting to match created types to an established SMIRNOFF.
For all files left blank, they will be taken from this module's
data/odds_files/ subdirectory.
usage smirky --molecules molfile --typetag fragmentType
[--atomORbases AtomORbaseFile --atomORdecors AtomORdecorFile
--atomANDdecors AtomANDdecorFile --bondORbase BondORbaseFile
--bondANDdecors BondANDdecorFile --atomIndexOdds AtomIndexFile
--bondIndexOdds BondIndexFile --replacements substitutions
--initialFragments initialFragments --SMIRNOFF referenceSMIRNOFF
--temperature float --verbose verbose
--iterations iterations --output outputFile]
example:
smirky -molecules AlkEthOH_test_filt1_ff.mol2 --typetag Angle
Options:
--version show program's version number and exit
-h, --help show this help message and exit
-m MOLECULES, --molecules=MOLECULES
Small molecule set (in any OpenEye compatible file
format) containing 'dG(exp)' fields with experimental
hydration free energies. This filename can also be an
option in this module's data/molecules sub-directory
-T TYPETAG, --typetag=TYPETAG
type of fragment being sampled, options are 'VdW',
'Bond', 'Angle', 'Torsion', 'Improper'
-e ODDFILES, --atomORbases=ODDFILES
Filename defining atom OR bases and associated
probabilities. These are combined with atom OR
decorators in SMIRKS, for example in
'[#6X4,#7X3;R2:2]' '#6' and '#7' are atom OR bases.
(OPTIONAL)
-O ODDFILES, --atomORdecors=ODDFILES
Filename defining atom OR decorators and associated
probabilities. These are combined with atom bases in
SMIRKS, for example in '[#6X4,#7X3;R2:2]' 'X4' and
'X3' are ORdecorators. (OPTIONAL)
-A ODDFILES, --atomANDdecors=ODDFILES
Filename defining atom AND decorators and associated
probabilities. These are added to the end of an atom's
SMIRKS, for example in '[#6X4,#7X3;R2:2]' 'R2' is an
AND decorator. (OPTIONAL)
-o ODDFILES, --bondORbase=ODDFILES
Filename defining bond OR bases and their associated
probabilities. These are OR'd together to describe a
bond, for example in '[#6]-,=;@[#6]' '-' and '=' are
OR bases. (OPTIONAL)
-a ODDFILES, --bondANDdecors=ODDFILES
Filename defining bond AND decorators and their
associated probabilities. These are AND'd to the end
of a bond, for example in '[#6]-,=;@[#7]' '@' is an
AND decorator.(OPTIONAL)
-D ODDSFILE, --atomOddsFile=ODDSFILE
Filename defining atom descriptors and probabilities
with making changes to that kind of atom. Options for
descriptors are integers corresponding to that indexed
atom, 'Indexed', 'Unindexed', 'Alpha', 'Beta', 'All'.
(OPTIONAL)
-d ODDSFILE, --bondOddsFile=ODDSFILE
Filename defining bond descriptors and probabilities
with making changes to that kind of bond. Options for
descriptors are integers corresponding to that indexed
bond, 'Indexed', 'Unindexed', 'Alpha', 'Beta', 'All'.
(OPTIONAL)
-s SMARTS, --substitutions=SMARTS
Filename defining substitution definitions for SMARTS
atom matches. (OPTIONAL).
-f SMARTS, --initialtypes=SMARTS
Filename defining initial (first) fragment types as
'SMIRKS typename'. If this is left blank the
initial type will be a generic form of the given
fragment, for example '[*:1]~[*:2]' for a bond
(OPTIONAL)
-r REFERENCE, --smirff=REFERENCE
Filename defining a SMIRNOFF force fielce used to
determine reference fragment types in provided set of
molecules. It may be an absolute file path, a path
relative to the current working directory, or a path
relative to this module's data subdirectory (for built
in force fields). (OPTIONAL)
-i ITERATIONS, --iterations=ITERATIONS
MCMC iterations.
-t TEMPERATURE, --temperature=TEMPERATURE
Effective temperature for Monte Carlo acceptance,
indicating fractional tolerance of mismatched atoms
(default: 0.1). If 0 is specified, will behave in a
greedy manner.
-p OUTPUT, --output=OUTPUT
Filename base for output information. This same base
will be used for all output files created. If None
provided then it is set to 'typetag_temperature'
(OPTIONAL).
-v VERBOSE, --verbose=VERBOSE
If True prints minimal information to the commandline
during iterations. (OPTIONAL)
``
## The SMIRNOFF force field format
The SMIRNOFF force field format is documented [here](https://github.com/openforcefield/openforcefield/blob/master/The-SMIRNOFF-force-field-format.md).
It was previously avaialbe in this repository, but has been moved.
SMIRNOFF99Frosst, a version of SMIRNOFF mirroring the parameters found in the parm@Frosst force field, is now housed in its own [repository](https://github.com/openforcefield/smirnoff99Frosst).
`forcefield.py` and other modules required to implement the SMIRNOFF format for simulations in OpenMM have also been moved. These scripts and examples on how to use them can be found at [openforcefield/openforcefield](https://github.com/openforcefield/openforcefield).
## References
[1] Green PJ. Reversible jump Markov chain Monte Carlo computation and Bayesian model determination. Biometrika 82:711, 1995.
http://dx.doi.org/10.1093/biomet/82.4.711