Class CC

• Defined in File cc.hpp

Nested Relationships

Nested Types

• Struct CC::Options

Class Documentation

class CC

CC is a derivation engine for the coupled-cluster method.

Public Types

enum class Ansatz

Values:

enumerator T

traditional ansatz

enumerator oT

traditional orbital-optimized (singles-free) ansatz

enumerator U

unitary ansatz

enumerator oU

unitary orbital-optimized (singles-free) ansatz

Public Functions

explicit CC(size_t n)

constructs CC engine with default options (traditional ansatz, screening enabled, topological optimization enabled)

Parameters:

n – coupled cluster excitation rank

explicit CC(size_t n, const Options &opts)

constructs CC engine with custom options

See also

CC::Options

Parameters:

• n – coupled cluster excitation rank

• opts – configuration options

Ansatz ansatz() const

Returns:

the type of ansatz

bool unitary() const

Returns:

true if the ansatz is unitary

bool screen() const

Returns:

whether screening is on or not

bool use_topology() const

Returns:

whether topological optimization is used in WickTheorem

std::vector<ExprPtr> t(size_t pmax = std::numeric_limits<size_t>::max(), size_t pmin = 0)

derives t amplitude equations, \( \langle P|\bar{H}|0 \rangle = 0 \)

Parameters:

• pmax – highest particle rank of the projector manifold \f \langle P | \f; the default value is to use the cluster operator rank of this engine

• pmin – lowest particle rank of the projector manifold \f \langle P | \f; the default value is 0

Returns:

vector of t amplitude equations, with element k containing equation \( \langle k |\bar{H}|0 \rangle = 0 \) for k in the [pmin,pmax] range, and null value otherwise

std::vector< ExprPtr > λ ()

derives λ amplitude equations, \( \langle 0| (1 + \hat{\Lambda}) \frac{d \bar{H}}{d \hat{T}_P} |0 \rangle = 0 \)

Returns:

vector of λ amplitude equations, with element k containing equation \( \langle 0| (1 + \hat{\Lambda}) \frac{d \bar{H}}{d \hat{T}_k} |0 \rangle = 0 \) for k in the [1,N] range; element 0 is always null

std::vector< ExprPtr > tʼ (size_t rank=1, size_t order=1, std::optional< size_t > nbatch=std::nullopt)

derives perturbed t amplitude equations

Parameters:

• rank – rank of perturbation operator. r = 1 means one-body perturbation operator

• order – order of perturbation

• nbatch – optional batching index rank for perturbation operators

Pre:

rank==1 && order==1, only first order perturbation and one-body perturbation operator is supported now

Returns:

std::vector of perturbed t amplitude equations

std::vector< ExprPtr > λʼ (size_t rank=1, size_t order=1, std::optional< size_t > nbatch=std::nullopt)

derives perturbed λ amplitude equations

Parameters:

• rank – rank of perturbation operator. r = 1 means one-body perturbation operator

• order – order of perturbation

• nbatch – optional batching index rank for perturbation operators

Pre:

rank==1 && order==1, only first order perturbation and one-body perturbation operator is supported now

Returns:

std::vector of perturbed λ amplitude equations

std::vector< ExprPtr > eom_r (nₚ np, nₕ nh)

derives right-side sigma equations for EOM-CC

Parameters:

• np – number of particle creators in R operator

• nh – number of hole creators in R operator

Returns:

vector of right side sigma equations, element 0 is always null

std::vector< ExprPtr > eom_l (nₚ np, nₕ nh)

derives left-side sigma equations for EOM-CC

Parameters:

• np – number of particle annihilators in L operator

• nh – number of hole annihilators in L operator

Returns:

vector of left side sigma equations, element 0 is always null

struct Options

Configuration options for CC class.

Public Members

Ansatz ansatz = Ansatz::T

type of CC ansatz. see CC::Ansatz

bool screen = true

if true, uses Operator level screening before applying WickTheorem. This propagates to all ref_av() calls

bool use_topology = true

if true, uses topological optimizations in WickTheorem

std::optional<size_t> hbar_comm_rank = std::nullopt

maximum order of nested commutators in H̄; must be specified if unitary ansatz is used

std::optional<size_t> pertbar_comm_rank = std::nullopt

maximum order of nested commutators in the similarity transformed perturbation operator; must be specified if unitary ansatz is used in perturbed amplitude derivation