qiskit.chemistry.MP2Info¶

class MP2Info(qmolecule, threshold=1e-12)[source]¶

A utility class for Moller-Plesset 2nd order (MP2) information

Each double excitation given by [i,a,j,b] has a coefficient computed using

coeff = -(2 * Tiajb - Tibja)/(oe[b] + oe[a] - oe[i] - oe[j])

where oe[] is the orbital energy

and an energy delta given by

e_delta = coeff * Tiajb

All the computations are done using the molecule orbitals but the indexes used in the excitation information passed in and out are in the block spin orbital numbering as normally used by the chemistry module.

A utility class for MP2 info

Parameters

qmolecule (QMolecule) – QMolecule from chemistry driver
threshold (float) – Computed coefficients and energy deltas will be set to zero if their value is below this threshold

__init__(qmolecule, threshold=1e-12)[source]¶

A utility class for MP2 info

Parameters

qmolecule (QMolecule) – QMolecule from chemistry driver
threshold (float) – Computed coefficients and energy deltas will be set to zero if their value is below this threshold

Methods

`__init__`(qmolecule[, threshold])	A utility class for MP2 info
`mp2_get_term_info`(excitation_list[, …])	With a reduced active space the set of used excitations can be less than allowing all available excitations.
`mp2_terms`([freeze_core, orbital_reduction])	Gets the set of MP2 terms for the molecule taking into account index adjustments due to frozen core and/or other orbital reduction

Attributes

`mp2_delta`	Get the MP2 delta energy correction for the molecule
`mp2_energy`	Get the MP2 energy for the molecule

property mp2_delta¶

Get the MP2 delta energy correction for the molecule

Returns: The MP2 delta energy
Return type: float

property mp2_energy¶

Get the MP2 energy for the molecule

Returns: The MP2 energy
Return type: float

mp2_get_term_info(excitation_list, freeze_core=False, orbital_reduction=None)[source]¶

With a reduced active space the set of used excitations can be less than allowing all available excitations. Given a (sub)set of excitations in the space this will return a list of correlation coefficients and a list of correlation energies ordered as per the excitation list provided.

Parameters

excitation_list (list) – A list of excitations for which to get the coeff and e_delta
freeze_core (bool) – Whether core orbitals are frozen or not
orbital_reduction (list) – An optional list of ints indicating removed orbitals

Returns

List of coefficients and list of energy deltas

Return type

Tuple(list, list)

Raises

ValueError – Excitation not present in mp2 terms

mp2_terms(freeze_core=False, orbital_reduction=None)[source]¶

Gets the set of MP2 terms for the molecule taking into account index adjustments due to frozen core and/or other orbital reduction

Parameters

freeze_core (bool) – Whether core orbitals are frozen or not
orbital_reduction (list) – An optional list of ints indicating removed orbitals

Returns

A dictionary of excitations where the key is a string in the form: from_to_from_to e.g. 0_4_6_10 and the value is a tuple of (coeff, e_delta)

Return type

dict