Calculators#

The evaluation of correlation energy and spectrum of a coupled system is handled by calculator objects. These calculators use different internal representations of the response functions of the polarizable objects that build up the coupled system.

CasidaCalculator#

class strongcoca.calculators.CasidaCalculator(coupled_system, broadening=NoArtificialBroadening, name='CasidaCalculator')[source]#

Instances of this class enable the calculation of correlation energy and spectrum of a coupled system, all polarizable objects in which have an internal representation in the form of a Casida matrix.

The calculations are done for discrete excitations, and continuous spectra calculated with this calculator use the given broadening.

Parameters:

  • coupled_system (CoupledSystem) – Coupled system for which to carry out calculations.

  • broadening (Broadening) – Artificial broadening used for the continuous response; defaults to no broadening.

  • name (str) – Name of response.

Examples

The following code snippet shows the calculation of the correlation energy for a simple demo system:

>>> from strongcoca import CoupledSystem, PolarizableUnit
>>> from strongcoca.response import build_random_casida
>>> from strongcoca.calculators import CasidaCalculator
>>>
>>> # construct coupled system
>>> response = build_random_casida(n_states=2, name='Tiger', random_seed=42)
>>> pu1 = PolarizableUnit(response, [0, 0, 0], name='Cheetah')
>>> pu2 = PolarizableUnit(response, [3, 0, 0], name='Leopard')
>>> cs = CoupledSystem([pu1, pu2])
>>>
>>> # set up calculator
>>> calc = CasidaCalculator(cs)
>>>
>>> # ... and compute the correlation energy
>>> calc.get_correlation_energy()
-0.050798240...
property excitations: Excitations#

Excitations as Excitations.

PolarizabilityCalculator#

class strongcoca.calculators.PolarizabilityCalculator(coupled_system, imaginary_frequencies, units='eV', name='PolarizabilityCalculator')[source]#

Instances of this class enable the calculation of correlation energy and spectrum of a coupled system, all polarizable objects in which have an internal representation in the form of a polarizability tensor.

Spectra calculated with this calculator derive broadening from the underlying polarizable units. Any additional or separate broadening is not added.

Parameters:

  • coupled_system (CoupledSystem) – Coupled system for which to carry out calculations.

  • imaginary_frequencies (Union[ndarray, Sequence[float]]) – Frequency grid along imaginary axis used for correlation energy calculation; eV by default, optionally atomic units (see units).

  • units (str) –

    eV to specify energies in eV or au to specify inputs in atomic units.

    This parameter determines whether conversion should be performed during initialization and has no effect on instance methods and variables.

  • name (str) – Name of response.

Examples

The following code snippet shows the calculation of the correlation energy for a simple demo system:

>>> import numpy as np
>>> from strongcoca import CoupledSystem, PolarizableUnit
>>> from strongcoca.response import build_random_casida
>>> from strongcoca.calculators import PolarizabilityCalculator
>>>
>>> # construct coupled system
>>> response = build_random_casida(n_states=2)
>>> pu1 = PolarizableUnit(response, [0, 0, 0])
>>> pu2 = PolarizableUnit(response, [2, 0, 0])
>>> cs = CoupledSystem([pu1, pu2])
>>>
>>> # set up calculator
>>> calc = PolarizabilityCalculator(cs, np.linspace(0, 10, 100))
>>>
>>> # ... and compute the correlation energy
>>> calc.get_correlation_energy()
-0.72084000362...
property coupling_matrix: ndarray#

The coupling matrix

\[\boldsymbol{T}_{ij} = \frac{3\boldsymbol{r}^{(ij)}(\boldsymbol{r}^{(ij)})^\text{T}}{\left|r^{(ij)}\right|^5} - \frac{1}{\left|r^{(ij)}\right|^3}\]

as a matrix where the rows and columns each correspond to the system index \(i\) or \(j\) and the Cartesian direction.

This quantity is calculated on first use and then buffered.