The ReaxFFParameters class provides a parameterizable interface to the ReaxFF reactive force field. It can be initialized by passing a force field path to the constructor:

ff = ReaxFFParameters('path/to/ffield.ff')

By default, all relevant parameters will be marked as is_active==True (i.e. marked for parameterization). See the API for parameter naming conventions. Reading Legacy params Files

Outside of the ParAMS formalism, a params file is common to mark a set of paramters for optimization, and set their respective ranges. Support for these files is implemented in the ReaxFFParameters.read_paramsfile() method:

ff = ReaxFFParameters('path/to/ffield.ff')

The method will mark all matching parameters as is_active=True (and deactivate all remaining ones). Will raise an error if blocks that are not present in the force field are referenced in the params file. Note that the 4th column in the params file (delta value) will be ignored. Addition of Parameters

The ReaxFF interface allows for the addition of new parameters through the add_blocks() method. Parameter Databases and Value Suggestions

The class can suggest suitable parameter values for a number of queried parameters. See the ReaxFFParameters.params_from_db() method for more information. By default, all force fields in $AMSHOME/atomicdata/ForceFields/ReaxFF will be used to return suggestions. Users can create their own databases from fewer (or more) force fields through the ReaxFFParameters.generate_paramsdb() method. ReaxFF Conversion Functions

Outside of ParAMS, ReaxFF is parameterized with a training set defined in trainset.in and geo files. There are two functions available to help with the conversion to the ParAMS format:

trainset_to_params(trainsetfile, use_weights=True, default_sigmas=None) → scm.params.core.dataset.DataSet

Converts an a ReaxFF trainset.in file to a DataSet object.

trainsetfile : str
Path to trainset.in.
use_weights : bool

If False, all weights will be set to 1.0, and Sigma will be set to the value from trainset.in

If True, then new_weight/(new_sigma**2) == 1/(value_from_trainset_in**2).

new_sigma is taken from the standard Sigma value for the pertinent extractor, or from the default_sigmas dictionary.

default_sigmas : dict

A dictionary of the type

{ ‘energy’: sigma_energy, ‘forces’: sigma_forces, ‘charges’: sigma_charges, ‘angles’: sigma_angles,

‘distance’: sigma_distance, ‘dihedral’: sigma_dihedral }

The sigma values should be given in the classic ReaxFF units, so kcal/mol for energy, angstrom for distance, etc.

The sigma values are taken from this dictionary only if use_weights == True


ds : DataSet instance

geo_to_params(geofile: str, normal_run_settings: Union[scm.plams.core.settings.Settings, str]) → scm.params.core.jobcollection.JobCollection

Convert a ReaxFF geo file to a JobCollection instance.

  • Each entry’s ID will be based on the DESCRP line. Duplicates will not be added.
  • Will guess the settings for each job based on the RUTYPE line. Can either be SinglePoint or GeometryOptimization (optionally with MaxIterations).
geofile : str
Path to geo file.
normal_run_settings : plams.Settings, str
A plams.Settings instance representing the NORMAL RUN or the path to a control file from which the settings will be extracted

jc : JobCollection ReaxFF Interface API

class ReaxFFParameters(ffieldfile, bounds_scale=1.2, settings=None)

Interface to the ReaxFF force field format.


In addition to the ones already availabe in BaseParameters

header : dict
A dictionary with metadata. header[‘head’] contains the first line of the force field
path : str
The path to the last written ffield file.
blocks : List[str]

Strings that mark valid parameter blocks. See ReaxFF manual for more information.


This is a class attribute, meaning that an instance can contain fewer blocks.

allnames : Dict[str : List[str]]

A dictionary with BLOCK_NAME:List[PARAMETER_NAMES], where BLOCK_NAME is one of the elements from blocks. See also name_to_index() and names_in_block().


This is a class attribute, meaning that an instance can contain fewer parameters.

shape : Dict[str : List[int]]
A dictionary of BLOCK_NAME:[NBLOCKS, N_PARAMS_IN_BLOCK], where BLOCK_NAME is one of the elements from blocks, NBLOCKS is the number of BLOCK_NAME blocks and N_PARAMS_IN_BLOCK is the number of parameters per block. See ReaxFF manual for more information.

Parameter Naming Conventions:

Naming follows the tables as documented in the ReaxFF manual.
The name string is generated from the table’s Name in Eq column.
All atom-specific parameter names will start with the atom prefix, followed by the name: At1.At2.At3:NAME. For example, the name of the first parameter in the atoms block for a Hydrogen will be H:r_0^sigma.
See below for a full list of names.
Each parameter in the ReaxFF interface has the following additional attributes: block, block_index, equation, description, atoms_reversible. For easy filitering of parameters, see get(). For conversions between block indices and name strings, see the blocks, name_to_index() and names_in_block().

class Parameter(block, block_index, atoms, bounds_scale=0, *a, **kw)
__init__(block, block_index, atoms, bounds_scale=0, *a, **kw)

Initialize self. See help(type(self)) for accurate signature.

__init__(ffieldfile, bounds_scale=1.2, settings=None)

Initialize the class instance, reading a ffied from ffieldfile.

ffieldfile : str
Path to the force field file.
bounds_scale : float >= 0

Apply arbitrary bounds, by providing a factor which will determine lower/upper bounds by b = x0 ± (bounds_scale-1)*abs(x0).


Bounds for any x0 == 0 will be set to +-1.

settings : optional, Settings
A plams.Settings instance that will be added to the output of get_engine(). Must have the input.ReaxFF keys defined.
get_engine(parameters=None, path=None, write=True)


When called without path, will store a ffield file in a temporary directory for as long as the returned Engine instance is referenced.

Returns:A ReaxFF Engine class matching the passed params, or the current set of parameters if None.
write(file=None, parameters=None)

Writes the current parameters to file.


When called without file, will store the ffield file in a temporary directory.
Use the path attribute to get the file path.

get_constraints() → List[scm.params.parameterinterfaces.base.Constraint]

Returns a list of physically reasonable Constraints for this instance to be passed to the Optimization.

Will constrain the covalent radii and bond lengths \(r_0\) for the \(\sigma, \pi, \pi\pi\) bonds to \(r_0^\sigma >= r_0^\pi >= r_0^\pi\pi\) and the Van der Waals radius \(r_\mathrm{VdW}\) to \(r_\mathrm{VdW}\) >= r_0^sigma`.


Reads a legacy params file, sets all matching parameters to is_active=True (i.e. flags them as paramters to be fitted), and adjusts each parameter’s ranges to the ones from paramsfile.

add_blocks(params: List[str], allow_duplicates=False)

Adds new parameters to the current instance.
The addition happens block-wise by providing a list of strings, where each string represents the addition of one block. Strings must have the form At1.At2.At3.At4, where At represents the chemical symbol of the desired element (separated by dots) and the number of elements determines the block to be added (1 for the atomic block, 2 for bonds, 3 for angles, 4 for torsions). For example,

>>> ffield.add_blocks(['C.O', 'C.O.H'])

adds the C-O bonds block and the C-O-H angles block to the ffield instance. Off-diagonals and hydrogen-bonds can be added by prefixing a string with OFD: and HBD: respectively:

>>> ffield.add_blocks(['OFD:C.O', 'HBD:O.H.C'])

The above will add the C-O off-diagonal and O-H-C hydrogen-bond block.


The following is of note when adding new blocks:

  • The addition of multiatomic blocks to a force field that does not yet contain all respective elements will automatically add the atomic block for that element. E.g., the addition of C-O to a force field that does not yet contain parameters for oxygen also implies the addition of O
  • Parameters added by this method have a value of 0. and a range of (-1, 1)
  • Already present blocks will not be overwritten, however, a duplicate block can be added by setting allow_duplicates=True
classmethod generate_paramsdb(paths=['$AMSHOME'], dbfile=None)

Generates a parameter database based on all force field files found in paths and stores it in dbfile.

paths : List[str]
When generating the database, each entry in paths can be either a directory, or a full path to a force field file. If a directory, will scan recursively and consider all files with the .ff ending.
dbfile : optional, str
Stores the generated database in dbfile. Defaults to $AMSHOME/scripting/scm/params/data/reaxffdb.gz.
classmethod params_from_db(params: List[str], dbfile=None, **subst_atoms) → List[collections.namedtuple]

Given a list of n parameter queries in params, scans a force field database stored in dbfile and returns n named tuples, which hold all parameters matching the query.

params : List[str]

Scans the data base for all entries in params. Each element is a string with either of the following syntaxes:

  • ‘BLOCK:At1.At2.At3.At4:INDEX’ or
  • ‘At1.At2.At3.At4:NAME’

where At1.At2.At3.At4 are chemical symbols (one to four). For the general block, this is replaced by None.

In the former case, BLOCK has to be any of {‘GEN’, ‘ATM’, ‘BND’, ‘OFD’, ‘ANG’, ‘TOR’, ‘HBD’} referring to the General, Atoms, Bonds, Off-Diagonals, Angles, Torsions, Hydrogen-Bonds blocks respectively. And INDEX is an integer specifying the parameter number for the block (starting with 0).

In the latter case, NAME refers to the string name of the desired parameter, following the same naming as in the names attribute (see Full List of Parameter Names).

dbfile: optional, str
Path to the database file to be used for the search. Defaults to a database generated from $AMSHOME/atomicdata/ForceFields/ReaxFF. See generate_paramsdb() for more information.
subst_atoms: optional keywords

Additional keywords will be interpreted as chemical elements (keys) that can be substitued by a number of other elements (values). This extends each query by matching all valid combinations of chemical elements for a specific parameter, rather than limiting it to one specific set of elements. Useful when queries should also include chemically similar elements.


>>> cls.params_from_db(['BND:C.O:0'], C=('Si', 'Ge'), O=('S',))

Will search all first entries of the bonds block considering the follwing combinaitons of elements: C.O, C.S, Ge.O, G.S, Si.O, Si.S.


Returns a list of named 4-tuples. Each element in the list corresponds to a query. Each named tuple unpacks to (query, parametername, values, atoms, sources). Elements within the tuple are stored in the respective attribute (e.g. tup.values).

query : str
String used for the query, Same as in params
parametername : str
String with the requested parameter’s name (excluding the chemical symbols prefix)
values : array
Array of all parameter values matching the query
atoms : array of str
Array of chemical elements corresponding to each returned parameter value
sources : array of str
Array of force field paths corresponding to the origin of each parameter value
classmethod block_from_db(block: str)
block : str
Should include the atoms. ‘GEN’, ‘BND:C.Cl’, ‘ANG:C.C.H’, etc.

Returns a 2-tuple containing a dictionary and a list of parameter names. The keys of the dictionary are the sources (paths to .ff files), and the values are lists of parameter values.

names_in_block(block: Union[str, int], atoms: str = '') → List[str]

Returns the names of the all parameters in block, optionally prepended by an {atoms}: string. block can either be a an int in the range of [0, 6] or any of {‘GEN’, ‘ATM’, ‘BND’, ‘OFD’, ‘ANG’, ‘TOR’, ‘HBD’} referring to the General, Atoms, Bonds, Off-Diagonals, Angles, Torsions, Hydrogen-Bonds blocks respectively.


Index numbering starts from zero

See also


classmethod name_to_index(name: str, block_as='str') → Tuple[Union[int, str], int]

Given a parameter name, returns the indices at which this name is located within the force field blocks. The name argument should be a string of At1.At2:NAME, where At are the atoms (one to four) the parameter affects.
If block_as==’str’, the returned value is a (str, int), otherwise (int, int), where the first element specifies the block and the second one the index at which this is parameter located within the block. Blocks are represented by an int in the range of [0, 6] or strings of {‘GEN’, ‘ATM’, ‘BND’, ‘OFD’, ‘ANG’, ‘TOR’, ‘HBD’} referring to the General, Atoms, Bonds, Off-Diagonals, Angles, Torsions, Hydrogen-Bonds blocks respectively.


Index numbering starts from zero.

copy_block(other_interface: scm.params.parameterinterfaces.reaxff.ReaxFFParameters, from_block: str, to_block: str = None, copy_range: bool = True, allow_duplicates=False)

Copies the values (and optionally ranges) of a whole parameter block from other_interface to this instance.

other_ff: ReaxFFParameters
Copy the parameters in the block from this other instance
from_block: str
‘BND:C.C’ or similar. It is also possible to copy the complete block, _i.e._ all values in ‘BND’ or ‘OFD’ by passing only the three-letter block name.
to_block : str or None
‘BND:C.O’ or similar. If None, set to the same value as from_block
copy_range: bool
Whether to copy the .range attribute from the other interface
get(name: str = None, atoms: str = None, block: Union[str, int] = None, index: int = None) → List[scm.params.parameterinterfaces.reaxff.ReaxFFParameters.Parameter]

Returns a list of parameters in self based on a set of filters. Filtering can be based on:

name : str
Match a all parameters with name. Can be exact in the form of At1.At2:NAME, where At are the atoms for a parameter, or fuzzy in the form of NAME, meaning that all paraemters with NAME (regardless of atoms) will be matched
atoms : str
A string of the form ‘C.H’, ‘C.C.H’, etc
block : str or int
Parameter block name (str) or index (int), matching :attr:blocks
index : int
The parameter at index within a block.
classmethod yaml_load(yamlfile, *a, **kw)

Loads a parameter interface from a (compressed) human-readable yamlfile. Child classes should call super() in this method before implementing their own routines. Full List of Parameter Names

General block, no prefix
  1. p_boc1
  2. p_boc2
  3. -p_coa2
  4. p_trip4
  5. p_trip3
  6. k_c2
  7. p_ovun6
  8. p_trip2
  9. p_ovun7
  10. p_ovun8
  11. p_trip1
  12. nonb_low,swa
  13. R_cut
  14. p_fe1
  15. p_val6
  16. p_lp1
  17. p_val9
  18. p_val10
  19. p_fe2
  20. p_pen2
  21. p_pen3
  22. p_pen4
  23. p_fe3
  24. p_tor2
  25. p_tor3
  26. p_tor4
  27. p_elho only if eReaxFF is enabled
  28. p_cot2
  29. p_vdW1
  30. cutoff*100
  31. p_coa4
  32. p_ovun4
  33. p_ovun3
  34. p_val8
  35. X_soft
  36. n/a 1
  37. p_val only if eReaxFF is enabled
  38. n/a 2
  39. p_coa3
  40. n/a 3
  41. n/a 4 only if eReaxFF is enabled
Atoms block, prefix: At1:
  1. r_0^sigma
  2. Val_i
  3. n/a 1
  4. r_vdW
  5. D_ij
  6. gamma_i
  7. r_0^pi
  8. Val_i^e
  9. alpha_ij
  10. 1/gamma_w
  11. Val_j^angle
  12. p_ovun5
  13. p_i^xel2 only if eReaxFF is enabled
  14. chi_i
  15. eta_i
  16. n/a 2
  17. r_0^pipi
  18. p_lp2
  19. n/a 3
  20. p_boc4
  21. p_boc3
  22. p_boc5
  23. C_i
  24. alpha_i only if eReaxFF is enabled
  25. p_ovun2
  26. p_val3
  27. beta_i only if eReaxFF is enabled
  28. Val_i^'boc
  29. p_val5
  30. p_c1
  31. p_c2
  32. p_c3
  33. C_i only if Lg dispersion is enabled
  34. R_eij only if Lg dispersion is enabled
Bonds block, prefix: At1.At2: (equivalent to At2.At1:)
  1. D_e^sigma
  2. D_e^pi
  3. D_e^pipi
  4. p_be1
  5. p_bo5
  6. Val'_i^boc
  7. p_bo6
  8. p_ovun1
  9. p_be2
  10. p_bo3
  11. p_bo4
  12. n/a
  13. p_bo1
  14. p_bo2
  15. delta'_i
  16. p_ij^xel1 only if eReaxFF is enabled
Off-diagonals block, prefix: At1.At2: (equivalent to At2.At1:)
  1. D_ij
  2. r_vdW
  3. alpha_ij
  4. r_0^sigma
  5. r_0^pi
  6. r_0^pipi
  7. C_i,C_lg,ij only if Lg dispersion is enabled
Angles block, prefix At1.At2.At3: (equivalent to At3.At2.At1, At2 is the central atom)
  1. Theta_0,0
  2. p_val1
  3. p_val2
  4. p_coa1
  5. p_val7
  6. p_pen1
  7. p_val4
Torsions block, prefix At1.At2.At3.At4: (equivalent to At4.At3.At2.A1:)
  1. V_1
  2. V_2
  3. V_3
  4. p_tor1
  5. p_cot1
  6. n/a 1
  7. n/a 2
Hydrogen Bonds block, prefix At1.H.At2: (NOT equivalent to At2.H.At1:)
  1. r_hb^0
  2. p_hb1
  3. -p_hb2
  4. -p_hb3 Parameter Categories

To guide your selection we have split the ReaxFF parameters into three categories:

  1. Standard: Parameters which are generally safe to optimize.
  2. Expert: Parameters which require some expert knowledge/insight. Generally, these are parameters which should be handled with more care and should only be tuned at the end of the parametrization process, if at all.
  3. DoNotOptimize: Parameters which should never be activated and changed through optimization. This final category generally represents parameters which act as boolean flags or switches, are not used by the force field, or contain physical constants like atomic mass.

Please note that these categorizations are entirely empirical and based only on in-house experience and expert knowledge. They are not definitive groupings, and serve only to better inform and guide your own decisions.

The category for each ReaxFF parameter is shown in a separate column of the GUI. When scripting it can be accessed via the metadata attribute of the Parameter class e.g. p.metadata.category or p.metadata['category'].