MeamElementPotential¶

class MeamElementPotential(particleType, latticeType, nearestNeighbors, alpha, beta, referenceDistance, referenceEnergy, scalingFactor, weightingFactors, rho, gamma, attrac=0.0, repuls=0.0, nn2=False, zbl=True)¶

Constructor of the potential.

Parameters:

particleType (ParticleType or ParticleIdentifier) – Identifier of the particle type.
latticeType (str) – Type of the reference structure.
nearestNeighbors (int) – Number of nearest neighbors in the reference structure.
alpha (float) – Exponential decay factor for pair potential.
beta (sequence of float) – Exponential decay factors for the background electron densities. Must be of length four.
referenceDistance (PhysicalQuantity of type length) – The nearest neighbor distance in the reference structure.
referenceEnergy (PhysicalQuantity of type energy) – The cohesive energy.
scalingFactor (float) – Scaling Factor in embedding function.
weightingFactors (sequence of float) – Weighting factors in the reference configuration. Must be of length three.
rho (float) – Element-dependent density scaling.
gamma (int) – Choice for gamma function.
attrac (float) – The attractive factor in the pair potential.
repuls (float) – The repulsive factor in the pair potential.
nn2 (bool) – Triggers second nearest neighbor formulation for symmetric pair.
zbl (bool) – Toggles zbl blending for small distances.

classmethod getAllParameterNames()¶: Return the names of all used parameters as a list.

getAllParameters()¶: Return all parameters of this potential and their current values as a <parameterName / parameterValue> dictionary.

static getDefaults()¶: Get the default parameters of this potential and return them in form of a dictionary of <parameter name, default value> key-value pairs.

getParameter(parameterName)¶: Get the current value of the parameter parameterName.

setParameter(parameterName, value)¶

Set the parameter parameterName to the given value.

Parameters:

parameterName (str) – The name of the parameter that will be modified.
value – The new value that will be assigned to the parameter parameterName.

Usage Examples¶

Define a MEAM potential for a SiO2 quartz crystal by adding particle types and interaction functions to the TremoloXPotentialSet.

# Set up lattice
vector_a = [5.4306, 0.0, 0.0]*Angstrom
vector_b = [0.0, 5.4306, 0.0]*Angstrom
vector_c = [0.0, 0.0, 5.4306]*Angstrom
lattice = UnitCell(vector_a, vector_b, vector_c)

# Define elements
elements = [Silicon, Silicon, Silicon, Silicon, Silicon, Silicon, Silicon,
            Silicon]

# Define coordinates
fractional_coordinates = [[ 0.  ,  0.  ,  0.  ],
                          [ 0.25,  0.25,  0.25],
                          [ 0.5 ,  0.5 ,  0.  ],
                          [ 0.75,  0.75,  0.25],
                          [ 0.5 ,  0.  ,  0.5 ],
                          [ 0.75,  0.25,  0.75],
                          [ 0.  ,  0.5 ,  0.5 ],
                          [ 0.25,  0.75,  0.75]]

# Set up configuration
bulk_configuration = BulkConfiguration(
    bravais_lattice=lattice,
    elements=elements,
    fractional_coordinates=fractional_coordinates
    )

# -------------------------------------------------------------
# Calculator
# -------------------------------------------------------------
potentialSet = TremoloXPotentialSet(name='MEAM_Si_2007')
potentialSet.addParticleType(ParticleType(
    symbol='Si',
    mass=28.0855*atomic_mass_unit,
    charge=None,
    sigma=None,
    sigma14=None,
    epsilon=None,
    epsilon14=None,
    atomicNumber=14,
    tags=[],
))


_option = MeamGlobalOption(
    delr=0.1*Angstrom,
    erose=2,
    wf_mixing=2,
    r_cut=4.5*Angstrom,
    augment_1st=0.0,
    embedding_negative=False,
    density_scaling=False,
)
potentialSet.addOption(_option)
_potential = MeamElementPotential(
    particleType=ParticleIdentifier('Si', []),
    latticeType='dia',
    nearestNeighbors=4,
    alpha=4.89890486934,
    beta=[3.55, 2.5, 0.0, 7.5, ],
    referenceDistance=2.35*Angstrom,
    referenceEnergy=4.63*eV,
    scalingFactor=0.58,
    weightingFactors=[1.8, 5.25, -2.61, ],
    rho=1.0,
    gamma=3,
    attrac=0.0,
    repuls=0.0,
    nn2=True,
    zbl=False,
)
potentialSet.addPotential(_potential)
_potential = MeamScreeningPotential(
    particleType1=ParticleIdentifier('Si', []),
    particleType2=ParticleIdentifier('Si', []),
    particleType3=ParticleIdentifier('Si', []),
    Cmin=1.41,
    Cmax=2.8,
)
potentialSet.addPotential(_potential)

calculator = TremoloXCalculator(parameters=potentialSet)
calculator.setVerletListsDelta(0.25*Angstrom)

bulk_configuration.setCalculator(calculator)
bulk_configuration.update()