qrunch.chemistry.calculators.coupled_cluster_calculator

Ground state energy calculator using coupled cluster theory.

Note that the ground_state_problem may restrict the orbital space, in which case this is not a standard coupled cluster calculation but a calculation with a truncated orbital space. In case of a restricted orbital space the inactive energy contribution associated with the active space is included in the ground_state_problem.

Classes

CoupledClusterGroundStateCalculator

Class for performing coupled cluster calculations (CCSD or CCSD(T)).

CoupledClusterGroundStateProblemCalculatorOptions

Options to use for coupled cluster ground state calculations.
class CoupledClusterGroundStateCalculator

Bases: object

Class for performing coupled cluster calculations (CCSD or CCSD(T)).

__init__(method: Literal['ccsd', 'ccsd_t'] | None = None, options: CoupledClusterGroundStateProblemCalculatorOptions | None = None) → None

Initialize an instance of CoupledClusterGroundStateCalculator.

Parameters:

  • method (Literal['ccsd', 'ccsd_t'] | None) – The coupled cluster method to use. Supported values are “ccsd” and “ccsd_t”. If None, defaults to “ccsd”.

  • options (CoupledClusterGroundStateProblemCalculatorOptions | None) – Options to use for the calculation. None results in default options.

Return type:

None

calculate(problem: GeneralGroundStateProblem) → GroundStateProblemCalculatorResult
calculate(problem: ReactionPathProblem) → ReactionPathProblemCalculatorResult

Solve the coupled cluster problem.

Note that the ground_state_problem may restrict the orbital space, in which case this is not a standard coupled cluster calculation but a calculation with a truncated orbital space. In case of a restricted orbital space the inactive energy contribution associated with the active space is included in the ground_state_problem.

The Hamiltonian for all geometries is assumed to be real.

Parameters:

problem (RestrictedGroundStateProblem | LazyRestrictedGroundStateProblem | UnrestrictedGroundStateProblem | LazyUnrestrictedGroundStateProblem | RestrictedReactionPathProblem | UnrestrictedReactionPathProblem) – The problem to calculate the ground state energy / energies for.

Return type:

GroundStateProblemCalculatorResult | ReactionPathProblemCalculatorResult

class CoupledClusterGroundStateProblemCalculatorOptions

Bases: DataclassPublicAPI

Options to use for coupled cluster ground state calculations.

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

Parameters:

  • canonicality_tolerance – Maximum allowed absolute value of any off-diagonal element of the Fock matrix. Must be set according to SCF convergence thresholds. Default tolerance is set according to default SCF convergence. (default=1e-6)

  • verbose – Verbosity level for the underlying PySCF coupled cluster calculation. Higher values produce more output. (default=0)

__init__(*, canonicality_tolerance: float = 1e-06, verbose: int = 0) → None
Parameters:

  • canonicality_tolerance (float)

  • verbose (int)

Return type:

None

canonicality_tolerance: float = 1e-06
verbose: int = 0