Force constant models¶
ForceConstantPotential¶

class
hiphive.
ForceConstantPotential
(cs, parameters)[source]¶ A finalized force constant model. Can produce force constants for any structure compatible with the structure for which the model was set up.
Parameters:  cs (ClusterSpace object) – The cluster space the model is based upon
 parameters (array) – The fitted paramteres

get_force_constants
(atoms)[source]¶ Return the force constants of a compatible structure.
Parameters: atoms (ASE Atoms object) – input structure Returns: Return type: ForceConstants object

orbit_data
¶ list – list of dictionaries containing detailed information for each orbit, e.g. cluster radius and force constant

primitive_structure
¶ ASE Atoms object – structure of the lattice
ForceConstantCalculator¶

class
hiphive.calculators.
ForceConstantCalculator
(fcs)[source]¶ This class provides an ASE calculator that can be used in conjunction with integrators and optimizers with the atomic simulation environment (ASE). To initialize an object of this class one must provide the ideal atomic configuration along with a compatible force constant model.
Parameters:  atoms_ideal (ASE Atoms object) – ideal (reference) configuration (i.e. without displacements)
 fcs (ForceConstants object) – the ForceConstants object must be compatible with the ideal (reference) configuration

calculate
(atoms=None, properties=['energy'], system_changes=['positions', 'numbers', 'cell', 'pbc', 'initial_charges', 'initial_magmoms'])[source]¶

compute_energy_and_forces
()[source]¶ Compute energy and forces.
Returns: energy and forces Return type: float, list of 3dimensional vectors

implemented_properties
= ['energy', 'forces']¶
ForceConstants¶

class
hiphive.
ForceConstants
(fc_dict=None, cluster_groups=None, fc_list=None, atoms=None)[source]¶ Container class for force constants.
Either specify fc_dict or both cluster_groups and fc_list.
Parameters:  fc_dict (dict) – dict which holds all force constants with clusters as keys and the respective force constant as value
 cluster_groups (list) – list of groups of clusters, clusters in the same group should have identical force constants.
 fc_list (list) – list of force constants, one force constant for each cluster group
 atoms (ASE Atoms object) – supercell corresponding to the fcs

_fc_dict
¶ dict – dictionary that holds all force constants with clusters as keys and the respective force constant as value

assert_acoustic_sum_rules
(order=None, tol=1e06)[source]¶ Asserts that acoustic sum rules are enforced for fcs
Parameters:  order (int, Optional) – specifies which order to check, if None all are checked
 tol (float) – numeric tolerance for checking sum rules
Raises: This method raise an assertion error if sum rules are not enforced.

atoms
¶ ASE Atoms object – supercell corresponding to force constants

clusters
¶

get_fc_array
(order)[source]¶ Return force constants in array format for specified order.
Parameters: order (int) – force constants for this order will be returned Returns: NumPy array with shape (N,)*order + (3,)*order where N is the number of atoms Return type: NumPy array

get_fc_dict
(order=None, permutations=False)[source]¶ Return force constant dictionary for one specific order.
Parameters:  order (int) – fcs returned for this order
 permutations (bool) – if True returns all permutations of cluster, else only force constants for sorted cluster
Returns: dictionary with keys corresponding to clusters and values to the respective force constant
Return type: dict

natoms
¶ int – Number of atoms (maximum index in a cluster +1)

orders
¶ list – List of the orders for which force constants exists

print_cluster
(cluster: tuple)[source]¶ Prints ForceConstants[cluster] in a nice format.
Parameters: cluster (tuple) – tuple of ints indicating the sites belonging to the cluster

static
read
(f)[source]¶ Load a ForceConstants instance from file
Parameters: f (string or file object) – name of input file (string) or stream to load from (file object)

sparse
¶ bool – If True the object was initialized with sparse data
Constraints¶

hiphive.
enforce_rotational_sum_rules
(cs, parameters, sum_rules, **kwargs)[source]¶ Enforces rotational sum rules by projecting parameters.
Note
The interface to this function might change in future releases.
Parameters:  cs (ClusterSpace) – the underlying cluster space
 parameters (array) – parameters to be constrained
 sum_rules (list of str) – type of sum rules to enforce; possible values: ‘Huang’, ‘BornHuang’
 ridge_alpha (float) – hyperparameter to the ridge regression algorithm; keyword argument passed to the optimizer; larger values specify stronger regularization, i.e. less correction but higher stability [default: 1e6]
 iterations (int) – number of iterations to run the projection since each step projects the solution down to each nullspace in serial; keyword argument passed to the optimizer [default: 10]
Returns: constrained parameters
Return type: array
Examples
The rotational sum rules can be enforced to the parameters before constructing a force constant potential as illustrated by the following snippet:
cs = ClusterSpace(reference_structure, cutoffs) sc = StructureContainer(cs) # add structures to structure container opt = Optimizer(sc.get_fit_data()) opt.train() new_params = enforce_rotational_sum_rules(cs, opt.parameters, sum_rules=['Huang', 'BornHuang']) fcp = ForceConstantPotential(cs, new_params)