qiskit.chemistry.algorithms.pes_samplers.HarmonicPotential¶

class HarmonicPotential(molecule)[source]¶

Implements a 1D Harmonic potential.

Input units are Angstroms (distance between the two atoms), and output units are Hartrees (molecular energy).

Parameters: molecule (Molecule) – the underlying molecule.
Raises: ValueError – Only implemented for diatomic molecules

__init__(molecule)[source]¶

Parameters: molecule (Molecule) – the underlying molecule.
Raises: ValueError – Only implemented for diatomic molecules

Methods

`__init__`(molecule)	type molecule `Molecule`
`dissociation_energy`([scaling])	Returns the estimated dissociation energy for the current fit.
`eval`(x)	After fitting the data to the fit function, predict the energy at a point x.
`fit`(xdata, ydata[, initial_vals, bounds_list])	Fits a potential to computed molecular energies.
`fit_function`(x, k, r_0, m_shift)	Functional form of the potential.
`fundamental_frequency`()	Returns the fundamental frequency for the current fit (in s^-1).
`get_equilibrium_geometry`([scaling])	Returns the interatomic distance corresponding to minimal energy.
`get_maximum_trusted_level`([n])	Returns the maximum energy level for which the particular implementation still provides a good approximation of reality.
`get_minimal_energy`([scaling])	Returns the smallest molecular energy for the current fit.
`get_num_modes`()	This (1D) potential represents a single vibrational mode
`get_trust_region`()	The potential will usually be well-defined (even if not useful) for arbitrary x so we return a fairly large interval here.
`process_fit_data`(xdata, ydata)	Mostly for internal use. Preprocesses the data passed to fit_to_data()
`update_molecule`(molecule)	Updates the underlying molecule.
`vibrational_energy_level`(n)	Returns the n-th vibrational energy level for the current fit (in Hartrees).
`wave_number`()	Returns the wave number for the current fit (in cm^-1).

dissociation_energy(scaling=1.0)[source]¶

Returns the estimated dissociation energy for the current fit.

Parameters: scaling (float) – Scaling to change units. (Default is 1.0 for Hartrees)
Return type: float
Returns: estimated dissociation energy

eval(x)[source]¶

After fitting the data to the fit function, predict the energy at a point x.

Parameters: x (float) – value to evaluate surface in
Return type: float
Returns: value of potential in point x

fit(xdata, ydata, initial_vals=None, bounds_list=None)[source]¶

Fits a potential to computed molecular energies.

Parameters

xdata (List[float]) – interatomic distance points (Angstroms)
ydata (List[float]) – molecular energies (Hartrees)
initial_vals (Optional[List[float]]) – Initial values for fit parameters. None for default. Order of parameters is k, r_0 and m_shift (see fit_function implementation)
bounds_list (Optional[Tuple[List[float], List[float]]]) – Bounds for the fit parameters. None for default. Order of parameters is k, r_0 and m_shift (see fit_function implementation)

Return type

None

static fit_function(x, k, r_0, m_shift)[source]¶

Functional form of the potential.

Parameters

x (float) – x parameter of harmonic potential functional form
k (float) – k parameter of harmonic potential functional form
r_0 (float) – r_0 parameter of harmonic potential functional form
m_shift (float) – m parameter of harmonic potential functional form

Return type

float

Returns

harmonic potential functional form

fundamental_frequency()[source]¶

Returns the fundamental frequency for the current fit (in s^-1).

Return type: float
Returns: fundamental frequency for the current fit

get_equilibrium_geometry(scaling=1.0)[source]¶

Returns the interatomic distance corresponding to minimal energy.

Parameters: scaling (float) – Scaling to change units. (Default is 1.0 for Angstroms)
Return type: float
Returns: geometry corresponding to minimal energy

get_maximum_trusted_level(n=0)¶

Returns the maximum energy level for which the particular implementation still provides a good approximation of reality. Default value of 100. Redefined where needed (see e.g. Morse).

Parameters: n (int) – vibronic mode
Return type: float
Returns: maximum_trusted_level setted

get_minimal_energy(scaling=1.0)[source]¶

Returns the smallest molecular energy for the current fit.

Parameters: scaling (float) – Scaling to change units. (Default is 1.0 for Hartrees)
Return type: float
Returns: smallest molecular energy for the current fit

get_num_modes()¶

This (1D) potential represents a single vibrational mode

Return type: int

get_trust_region()¶

The potential will usually be well-defined (even if not useful) for arbitrary x so we return a fairly large interval here. Redefine in derived classes if needed.

Return type: Tuple[float, float]

classmethod process_fit_data(xdata, ydata)[source]¶

Mostly for internal use. Preprocesses the data passed to fit_to_data(): so that only the points around the minimum are fit (which gives more accurate vibrational modes).

Parameters

xdata (List[float]) – xdata to be considered
ydata (List[float]) – ydata to be considered

Return type

Tuple[list, list]

Returns

the processed data that fit better to a harmonic potential

update_molecule(molecule)[source]¶

Updates the underlying molecule.

Parameters: molecule (Molecule) – chemistry molecule
Raises: ValueError – Only implemented for diatomic molecules
Return type: Molecule

vibrational_energy_level(n)[source]¶

Returns the n-th vibrational energy level for the current fit (in Hartrees).

Parameters: n (int) – vibrational mode
Return type: float
Returns: vibrational energy level for the current fit

wave_number()[source]¶

Returns the wave number for the current fit (in cm^-1).

Return type: int
Returns: wave number for the current fit