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Excited states

Available since Sierra v1.5.0.

The ExcitationInput provides means to calculate excitation energies as well as transition properties for excitations from the ground state, using time-dependent linear-response theory. So far, this is incompatible with XTBMethod.

The results of a ExcitationInput calculation are stored in the ExcitationResult object.

Example

The following example demonstrates how to perform an excited-state calculation:

import sierra
from sierra.inputs import *

water = Molecule(pubchem="water")

# Perform TDDFT calculation with the B97-3c functional
tddft_inp = ExcitationInput(molecule=water, method=DFTMethod(xc="b97-3c"))
tddft_result = sierra.run(tddft_inp)
print("Excitation energies for water:")
#> Excitation energies for water:
print(tddft_result.excitation_energies)
#> [0.25722925 0.26468329 0.32774599]

ExcitationInput

Fields

method

The computational method for this call

molecule

The molecule the result is computed with

n_states

The number of states for which excitation energies and excitation properties shall be calculated.

  • Type: int
  • Default: 3
spin

The spin of the excited states to be calculated. For spin-restricted methods, the allowed values are 'singlet', 'triplet' and 'mixed', where 'mixed' will calculate singlet and triplet states. For spin-unrestricted methods, only 'mixed' is allowed.

  • Type: ExcitationSpin
  • Default: ExcitationSpin.mixed
tda

Whether to use the Tamm-Dancoff Approximation.

  • Type: bool
  • Default: False
details

Additional detail parameters to supply to the computation

Detail Fields

energy_threshold

threshold for energy convergence

  • Type: Optional[float]
result_contract
store_extras

This field determines the amount of output that is kept in the 'extras' field in addition to the requirements of the contract. 'True' will lead to storing all available information and 'False' will lead to storing no information beyond the requirements of the contract. Alternatively, a list of field names can be provided that shall be stored.

  • Type: One of: [bool, List[str]]
  • Default: False

ExcitationResult

Fields

All the fields in ExcitationInput and the following:

excitation_energies

The excitation energy for each calculated excitation.

  • Type: Array
extras

Additional key/value pairs generated during the computation.

  • Type: Mapping[str, Any]
  • Default: {}
oscillator_strengths

The oscillator strength for a each calculated excitation.

  • Type: Array
s_squared_values

The expectation value of the S^2 operator for each calculated excitation.

  • Type: Array
transition_dipole_moments

The transition dipole moment for each calculated excitation.

  • Type: Array
  • Additional Details: shape: (-1, 3)