qrunch.chemistry.calculators.configuration_interaction_calculator

Ground state energy calculator using (Pair) Configuration Interaction.

Note that the ground_state_problem may restrict the orbital space - in which case this is not a full configuration interaction (FCI) calculation but a CASCI calculation. However, we consider this a FCI calculation in the provided orbital space, and in case of a restricted orbital space the inactive energy contribution associated with the CAS is included in the energy_correction of the ground_state_problem.

The Pair Configuration Interaction (pCI) is a version of the configuration interaction (CI) where only pair excitations are included in the calculation. The Orbital Optimized Pair Full Configuration Interaction (oo-pFCI) is the orbital optimized version. Furthermore, a second-order correction to the pCI energy can be applied to account for the neglected excitations.

Classes

`ConfigurationInteractionGroundStateCalculator`	Class for performing configuration interaction calculations.
`OrbitalOptimizedPairConfigurationInteractionGroundStateCalculator`	Class for performing orbital-optimized pair configuration interaction calculations.
`PairConfigurationInteractionGroundStateCalculator`	Class for performing configuration interaction calculations with paired electrons.
`SecondOrderCorrectedPairConfigurationInteractionGroundStateCalculator`	Class for second-order corrected pair configuration interaction calculations.

class ConfigurationInteractionGroundStateCalculator

Bases: object

Class for performing configuration interaction calculations.

__init__(options: ConfigurationInteractionGroundStateProblemCalculatorOptions | None = None) → None

Initialize an instance of ConfigurationInteractionGroundStateCalculator.

Parameters:: options (ConfigurationInteractionGroundStateProblemCalculatorOptions | None) – Options to use for the calculation. None results in default options.
Return type:: None

calculate(problem: RestrictedGroundStateProblem | UnrestrictedGroundStateProblem) → GroundStateProblemCalculatorResult

calculate(problem: RestrictedReactionPathProblem | UnrestrictedReactionPathProblem) → ReactionPathProblemCalculatorResult

Solve the configuration interaction (CI) calculation.

Note that the problem may restrict the orbital space - in which case this is not a FCI calculation but a CASCI calculation. However, we consider this a FCI calculation in the provided orbital space, and in case of a restricted orbital space the inactive energy contribution associated with the CAS is included in the energy_correction of the problem.

The Hamiltonian for all geometries is assumed to be real.

Parameters:: problem – The problem to calculate the ground state energy / energies for.

class OrbitalOptimizedPairConfigurationInteractionGroundStateCalculator

Bases: object

Class for performing orbital-optimized pair configuration interaction calculations.

__init__(options: OrbitalOptimizerOptions | None = None, basin_hopping_options: BasinHoppingOptions | None = None) → None

Initialize an instance of OrbitalOptimizedPairConfigurationInteractionGroundStateCalculator.

Parameters:

options (OrbitalOptimizerOptions | None) – Options to use for the calculation. None results in default options.
basin_hopping_options (BasinHoppingOptions | None) – Options to use for basin hopping.

Return type:

None

calculate(problem: RestrictedGroundStateProblem | UnrestrictedGroundStateProblem) → GroundStateProblemCalculatorResult

calculate(problem: RestrictedReactionPathProblem | UnrestrictedReactionPathProblem) → ReactionPathProblemCalculatorResult

Solve the orbital-optimized pair configuration interaction (pCI) calculation.

Note that the problem may restrict the orbital space - in which case this is not a oo-pFCI calculation but a oo-pCASCI calculation. However, we consider this a FCI calculation in the provided orbital space, and in case of a restricted orbital space the inactive energy contribution associated with the CAS is included in the energy_correction of the problem.

The Hamiltonian for all geometries is assumed to be real.

Parameters:: problem – The problem to calculate the ground state energy / energies for.

class PairConfigurationInteractionGroundStateCalculator

Bases: object

Class for performing configuration interaction calculations with paired electrons.

__init__() → None

Initialize an instance of PairConfigurationInteractionGroundStateCalculator.

Return type:: None

calculate(problem: RestrictedGroundStateProblem | UnrestrictedGroundStateProblem) → GroundStateProblemCalculatorResult

calculate(problem: RestrictedReactionPathProblem | UnrestrictedReactionPathProblem) → ReactionPathProblemCalculatorResult

Solve the pair full configuration interaction (pFCI) calculation.

The Pair Configuration Interaction is a version of the configuration interaction where only pair excitations are included in the calculation.

Note that the problem may restrict the orbital space - in which case this is not a pFCI calculation but a pCASCI calculation. However, we consider this a FCI calculation in the provided orbital space, and in case of a restricted orbital space the inactive energy contribution associated with the CAS is included in the energy_correction of the problem.

The Hamiltonian for all geometries is assumed to be real.

Parameters:: problem – The problem to calculate the ground state energy / energies for.

class SecondOrderCorrectedPairConfigurationInteractionGroundStateCalculator

Bases: object

Class for second-order corrected pair configuration interaction calculations.

__init__(calculator: OrbitalOptimizedPairConfigurationInteractionGroundStateCalculator | PairConfigurationInteractionGroundStateCalculator) → None

Initialize an instance of SecondOrderCorrectedPairConfigurationInteractionGroundStateCalculator.

Parameters:: calculator (OrbitalOptimizedPairConfigurationInteractionGroundStateCalculator | PairConfigurationInteractionGroundStateCalculator) – The (possibly orbital optimized) pair configuration interaction calculator.
Return type:: None

calculate(problem: RestrictedGroundStateProblem | UnrestrictedGroundStateProblem) → GroundStateProblemCalculatorResult

calculate(problem: RestrictedReactionPathProblem | UnrestrictedReactionPathProblem) → ReactionPathProblemCalculatorResult

Solve the (orbital-optimized) pair configuration interaction (pCI) calculation with a second-order correction.

Note that the ground_state_problem may restrict the orbital space - in which case this is not a oo-pFCI calculation but a oo-pCASCI calculation. However, we consider this a FCI calculation in the provided orbital space, and in case of a restricted orbital space the inactive energy contribution associated with the CAS is included in the energy_correction of the ground_state_problem.

The Hamiltonian for all geometries is assumed to be real.

Parameters:: problem – The problem to calculate the ground state energy / energies for.