Force constant models

ForceConstantPotential

class hiphive.ForceConstantPotential(cs, parameters)

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)

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

static read(f)

Load a ForceConstantPotential object from a pickle file.

Parameters:f (str or file object) – name of input file (str) or stream to load from (file object) Returns:the original object as stored in the file Return type:ForceConstantPotential object

write(f)

Write a ForceConstantPotential instance to a pickle file.

Parameters:f (str or file object) – name of input file (str) or stream to write to (file object)

ForceConstantCalculator

class hiphive.calculators.ForceConstantCalculator(fcs)

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'])

compute_energy_and_forces()

Compute energy and forces.

Returns:energy and forces Return type:float, list of 3-dimensional vectors

implemented_properties = ['energy', 'forces']

ForceConstants

class hiphive.ForceConstants(fc_dict=None, cluster_groups=None, fc_list=None, atoms=None)

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=1e-06)

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)

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)

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)

Prints ForceConstants[cluster] in a nice format.

Parameters:cluster (tuple) – tuple of ints indicating the sites belonging to the cluster

static read(f)

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

write(f)

Write a ForceConstants instance to a file.

Parameters:f (str or file object) – name of input file (str) or stream to write to (file object)

Constraints

hiphive.enforce_rotational_sum_rules(cs, parameters, sum_rules, **kwargs)

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’, ‘Born-Huang’
• 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: 1e-6]
• 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', 'Born-Huang'])
fcp = ForceConstantPotential(cs, new_params)