HarmonicPotential
class HarmonicPotential(molecule)
Bases: qiskit.chemistry.algorithms.pes_samplers.potentials.potential_base.PotentialBase
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
Methods
dissociation_energy
HarmonicPotential.dissociation_energy(scaling=1.0)
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
HarmonicPotential.eval(x)
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
HarmonicPotential.fit(xdata, ydata, initial_vals=None, bounds_list=None)
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
fit_function
static HarmonicPotential.fit_function(x, k, r_0, m_shift)
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
HarmonicPotential.fundamental_frequency()
Returns the fundamental frequency for the current fit (in s^-1).
Return type
float
Returns
fundamental frequency for the current fit
get_equilibrium_geometry
HarmonicPotential.get_equilibrium_geometry(scaling=1.0)
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
HarmonicPotential.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
HarmonicPotential.get_minimal_energy(scaling=1.0)
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
HarmonicPotential.get_num_modes()
This (1D) potential represents a single vibrational mode
Return type
int
get_trust_region
HarmonicPotential.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]
process_fit_data
classmethod HarmonicPotential.process_fit_data(xdata, ydata)
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
HarmonicPotential.update_molecule(molecule)
Updates the underlying molecule.
Parameters
molecule (Molecule) – chemistry molecule
Raises
ValueError – Only implemented for diatomic molecules
Return type
Molecule
vibrational_energy_level
HarmonicPotential.vibrational_energy_level(n)
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
HarmonicPotential.wave_number()
Returns the wave number for the current fit (in cm^-1).
Return type
int
Returns
wave number for the current fit