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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 examples demonstrate 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)
#> [0.2572294096557424 0.26468341549614366 0.32774610065955756]

ExcitationInput

Fields

All of the fields in SingleInput and the following:

n_states

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

  • Type: int
  • Default: 3
tda

Whether to use the Tamm-Dancoff Approximation. Setting this to True will make the calculation faster but less accurate.

  • Type: bool
  • Default: False
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: str
  • Default: "mixed"

ThermodynamicsResult

Fields

All of the fields in SingleResult and the following:

excitation_energies

The excitation energy for each calculated excitation.

  • Type: Array[EnergyQuantity]
transition_dipole_moments

The transition dipole moment for each calculated excitation.

  • Type: List[Tuple[DipoleMomentQuantity, DipoleMomentQuantity, DipoleMomentQuantity]]
oscillator_strengths

The oscillator strength for a each calculated excitation.

  • Type: Array[float]
s_squared_values

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

  • Type: Array[float]