qrunch.chemistry.ground_state_problem.calculators.pair_configuration_interaction_calculators

Ground state energy calculator using Pair Full CI.

The Pair Full Configuration Interaction (pFCI) is a version of the full configuration interaction (FCI) where only pair excitations are included in the calculation. The Orbital Optimized Pair Full Configuration Interaction (oo-pFCI) is the orbital optimized version.

Module Attributes

DEFAULT_OPTIONS

The default options for the Orbital Optimizer minimizer.

Functions

`build_pair_bit_string_integers`(...)	Generate all pair excitation bitstrings from the electronic configuration.
`generate_pair_excitations`(reference, ...)	Generate all pair excitation bitstrings.
`log_scipy_result`(result)	Log details from scipy OptimizeResult in a readable format.

Classes

`BasinHoppingOptions`	Options for SciPy basinhopping global optimization.
`OrbitalOptimizedPairConfigurationInteractionGroundStateProblemCalculator`	Class for performing orbital-optimized pair full configuration interaction calculations.
`OrbitalOptimizerOptions`	The default options for SciPy minimizer.
`PairConfigurationInteractionGroundStateProblemCalculator`	Class for performing pair full configuration interaction calculations.
`SecondOrderCorrectedPairConfigurationInteractionGroundStateProblemCalculator`	Class for second-order corrected pair full configuration interaction calculations.

class BasinHoppingOptions

Bases: DataclassPublicAPI

Options for SciPy basinhopping global optimization.

All fields are immutable (frozen=True) so an instance can be safely reused.

Parameters:

number_of_macro_iterations – How many basin hopping steps to perform. (default=3)
temperature – Controls accept probability for worse solutions. (default=0.01)
stepsize – Size of random displacement. (default=0.05)
number_of_successive_failures – Stop if no improvement after this many steps. (default=4)
seed – RNG seed for reproducibility. (default=None)
display – Verbosity. (default=True)
active – Activate Basin Hopping. (default=True)

__init__(*, number_of_macro_iterations: int = 3, temperature: float = 0.01, stepsize: float = 0.05, number_of_successive_failures: int = 4, seed: int | None = None, display: bool = True, active: bool = True) → None

Parameters:

number_of_macro_iterations (int)
temperature (float)
stepsize (float)
number_of_successive_failures (int)
seed (int | None)
display (bool)
active (bool)

Return type:

None

active: bool = True

display: bool = True

number_of_macro_iterations: int = 3

number_of_successive_failures: int = 4

seed: int | None = None

stepsize: float = 0.05

temperature: float = 0.01

DEFAULT_OPTIONS = OrbitalOptimizerOptions(relative_error_tolerance=1e-06, max_iterations_per_parameter=20000, jacobian_step_size=1e-08, display=True): The default options for the Orbital Optimizer minimizer.

class OrbitalOptimizedPairConfigurationInteractionGroundStateProblemCalculator

Bases: object

Class for performing orbital-optimized pair full configuration interaction calculations.

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

Initialize an instance of OrbitalOptimizedPairConfigurationInteractionGroundStateProblemCalculator.

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(ground_state_problem: RestrictedGroundStateProblem | UnrestrictedGroundStateProblem) → GroundStateProblemCalculatorResult

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

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 the ground state problem is assumed to be real.

Parameters:: ground_state_problem (RestrictedGroundStateProblem | UnrestrictedGroundStateProblem) – The Ground state problem to calculate energy for.
Return type:: GroundStateProblemCalculatorResult

class OrbitalOptimizerOptions

Bases: DataclassPublicAPI

The default options for SciPy minimizer.

All fields are immutable (frozen=True) so an instance can be safely reused.

Parameters:

relative_error_tolerance – Convergence tolerance (default=1.0e-6)
max_iterations_per_parameter – Maximum number of iterations per parameter. (default=20000)
jacobian_step_size – Jacobian step size (default=1e-8)
display – (default=True)

__init__(*, relative_error_tolerance: float = 1e-06, max_iterations_per_parameter: int = 20000, jacobian_step_size: float = 1e-08, display: bool = True) → None

Parameters:

relative_error_tolerance (float)
max_iterations_per_parameter (int)
jacobian_step_size (float)
display (bool)

Return type:

None

display: bool = True

jacobian_step_size: float = 1e-08

max_iterations_per_parameter: int = 20000

relative_error_tolerance: float = 1e-06

class PairConfigurationInteractionGroundStateProblemCalculator

Bases: object

Class for performing pair full configuration interaction calculations.

__init__() → None

Initialize an instance of PairConfigurationInteractionGroundStateProblemCalculator.

Return type:: None

calculate(ground_state_problem: RestrictedGroundStateProblem | UnrestrictedGroundStateProblem) → GroundStateProblemCalculatorResult

Solve the pair full configuration interaction (pFCI) calculation.

Note that the ground_state_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 ground_state_problem.

The Hamiltonian for the ground state problem is assumed to be real.

Parameters:: ground_state_problem (RestrictedGroundStateProblem | UnrestrictedGroundStateProblem) – The Ground state problem to calculate energy for.
Return type:: GroundStateProblemCalculatorResult

class SecondOrderCorrectedPairConfigurationInteractionGroundStateProblemCalculator

Bases: object

Class for second-order corrected pair full configuration interaction calculations.

__init__(calculator: OrbitalOptimizedPairConfigurationInteractionGroundStateProblemCalculator | PairConfigurationInteractionGroundStateProblemCalculator) → None

Initialize an instance of OrbitalOptimizedPairConfigurationInteractionGroundStateProblemCalculator.

Parameters:: calculator (OrbitalOptimizedPairConfigurationInteractionGroundStateProblemCalculator | PairConfigurationInteractionGroundStateProblemCalculator) – The pair full configuration interaction calculator.
Return type:: None

calculate(ground_state_problem: RestrictedGroundStateProblem | UnrestrictedGroundStateProblem) → GroundStateProblemCalculatorResult

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

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 the ground state problem is assumed to be real.

Parameters:: ground_state_problem (RestrictedGroundStateProblem | UnrestrictedGroundStateProblem) – The Ground state problem to calculate energy for.
Return type:: GroundStateProblemCalculatorResult

build_pair_bit_string_integers(electronic_configuration: MolecularElectronConfiguration) → list[int]

Generate all pair excitation bitstrings from the electronic configuration.

Parameters:: electronic_configuration (MolecularElectronConfiguration) – The electronic configuration.
Return type:: list[int]

generate_pair_excitations(reference: int, total_length: int) → list[int]

Generate all pair excitation bitstrings.

The pair excitation bitstrings are generated as integers from the reference integer provided. It should represent a binary string composed of two identical halves.

Parameters:

reference (int) – Reference bitstring as integer.
total_length (int) – Total bit length of the binary string; must be even.

Return type:

list[int]

log_scipy_result(result: OptimizeResult) → None

Log details from scipy OptimizeResult in a readable format.

Parameters:: result (OptimizeResult) – The scipy OptimizeResult.
Return type:: None