occ::qm Namespace Reference

quantum mechanics/quantum chemistry functionality including Hartree-Fock and more More...

Namespaces
namespace	basis_sets
namespace	block
namespace	cc
namespace	cint
namespace	cosx
namespace	guess
namespace	impl
namespace	orb

Classes
class	ADIIS
	ADIIS (Augmented Direct Inversion in Iterative Subspace) Based on Hu & Yang, J. More...
struct	AutoAuxResult
	Statistics about the auto auxiliary basis generation. More...
class	CanonicalOrthogonalizer
class	CDIIS
class	ConvergenceAccelerator
	Encapsulates SCF convergence acceleration strategies (CDIIS, EDIIS, ADIIS) More...
class	CoulombMetric
	Factorization of a density-fitting Coulomb metric V = (P|Q). More...
class	DFIntegrals
	Builds metric-folded density-fitting "B" tensors for correlated methods. More...
class	EDIIS
struct	Energy
struct	FockBuildProperties
	What a method guarantees about its Fock build, so the SCF driver can decide whether to accumulate F += G(ΔD) instead of rebuilding from H each cycle. More...
class	GradientEvaluator
struct	Guess
	The starting point a guess produces. More...
struct	GuessRequest
	What a guess needs to know about the system. More...
class	HartreeFock
class	HessianEvaluator
	Evaluates molecular Hessian matrices (second derivatives of energy) More...
class	IntegralEngine
class	IntegralEngineDF
struct	JKPair
struct	JKTriple
class	MOIntegralEngine
	Lightweight holder of molecular-orbital information for post-HF methods, plus a brute-force single MO electron-repulsion integral evaluator kept as a reference/testing utility. More...
struct	MolecularOrbitals
class	MP2
struct	Oniom
struct	OrbitalSmearing
struct	PointChargePotential
	Plain external point charges (vacuum Coulomb). More...
class	PostHFMethod
struct	SCF
struct	SCFContext
struct	SCFConvergenceSettings
class	SCFMethodBase
class	ScopedRangeSeparation
	Applies a range-separation parameter for the duration of a scope, and puts back whatever was there before however the scope is left. More...
class	SplitRIJ
	Split-RI-J: Coulomb matrix via Hermite Gaussian basis (Neese 2003) More...
struct	Wavefunction
struct	WolfPointChargePotential
	Wolf-summed periodic point charges. More...

Concepts
concept	ExternalPotential
	Concept for an external-potential model: a self-contained engine that produces a one-electron potential matrix V_ext and the nuclear–external interaction energy when handed an SCF procedure (HF/DFT/etc.).
concept	SCFMethod
concept	DensityFittingMethod
concept	PointChargeMethod

Typedefs
using	PointChargeList = std::vector< occ::core::PointCharge >
using	DispersionGradientFunc = std::function< std::pair< double, Mat3N >(const AOBasis &, const MolecularOrbitals &, int)>
	Callback that computes a dispersion energy and nuclear gradient for the given basis / orbitals / charge.
using	HessianMatrix = Mat
using	ShellPairList = std::vector< std::vector< size_t > >

Enumerations
enum class	FittingKind { JK , Correlation }
enum class	DispersionType { None , D4 }
enum class	GuessKind {   Auto , Core , Soad , Sap ,   AtomicScf }
	Where the SCF starts from. More...
enum class	CoulombMethod { Traditional , SplitRIJ }
	Method for computing Coulomb matrix in density fitting. More...
enum class	DiisStrategy { CDIIS , EDIIS_CDIIS , ADIIS_CDIIS }
	Strategy for DIIS extrapolation during SCF. More...
enum class	SpinComponent { Total , Alpha , Beta }

Functions
AutoAuxResult	generate_auto_aux (const AOBasis &basis, double threshold=1e-7, std::optional< int > max_l=std::nullopt)
	Generate automatic auxiliary basis using pivoted Cholesky decomposition Based on Lehtola, J.
Vec	chelpg_charges (const Wavefunction &wfn)
template<SpinorbitalKind kind, typename TA >
TA::Scalar	expectation (const TA &left, const TA &right)
template<typename TA >
TA::Scalar	expectation (SpinorbitalKind sk, const TA &left, const TA &right)
std::string	resolve_fitting_basis (const std::string &orbital_basis_name, FittingKind kind)
int	cosx_nbf_crossover ()
std::string_view	guess_kind_name (GuessKind kind)
const std::vector< std::pair< std::string, GuessKind > > &	guess_kind_names ()
	The names a user may write, and what each selects.
std::optional< GuessKind >	guess_kind_from_string (std::string_view name)
	Parse a guess name. Returns nothing for an unrecognised one.
bool	minimal_basis_covers (const gto::AOBasis &basis)
	Whether the shipped minimal basis has shells for every atom in basis.
GuessKind	select_guess (GuessKind requested, const gto::AOBasis &basis)
	Resolve Auto into a concrete kind; anything else passes through unchanged, so an explicit request is honoured even where it is a poor choice.
Guess	build_guess (GuessKind kind, const GuessRequest &request)
	Build kind for request.
template<typename T >
	ScopedRangeSeparation (T &, double) -> ScopedRangeSeparation< T >
void	from_json (const nlohmann::json &J, Energy &energy)
void	to_json (nlohmann::json &J, const Energy &energy)
std::pair< Mat, Vec >	merge_molecular_orbitals (const Mat &, const Mat &, const Vec &, const Vec &, bool sort_by_energy=false)
AOBasis	merge_basis_sets (const AOBasis &, const AOBasis &)
std::vector< occ::core::Atom >	merge_atoms (const std::vector< occ::core::Atom > &, const std::vector< occ::core::Atom > &)
Vec	mulliken_partition (const AOBasis &basis, const MolecularOrbitals &mo, Eigen::Ref< const Mat > op)
constexpr bool	supports_incremental_fock_build (const FockBuildProperties &properties)
	F can only be accumulated when the build is linear and the core Hamiltonian is fixed; screening decides whether it is worth doing.
template<SpinorbitalKind sk, Shell::Kind kind>
Mat	shellblock_norm (const AOBasis &basis, const Mat &matrix) noexcept
template<SpinorbitalKind kind>
constexpr std::pair< size_t, size_t >	matrix_dimensions (size_t nbf)
constexpr std::pair< size_t, size_t >	matrix_dimensions (SpinorbitalKind kind, size_t nbf)

Variables
template<typename T >
constexpr bool	is_scf_method_v = SCFMethod<T>
template<typename T >
constexpr bool	supports_density_fitting_v = DensityFittingMethod<T>
template<typename T >
constexpr bool	supports_point_charges_v = PointChargeMethod<T>

Detailed Description

quantum mechanics/quantum chemistry functionality including Hartree-Fock and more

Typedef Documentation

DispersionGradientFunc

using occ::qm::DispersionGradientFunc = typedef std::function<std::pair<double, Mat3N>( const AOBasis &, const MolecularOrbitals &, int)>

Callback that computes a dispersion energy and nuclear gradient for the given basis / orbitals / charge.

Used to inject corrections (e.g. XDM) that live in libraries above occ_qm, so occ_qm need not depend on them.

HessianMatrix

using occ::qm::HessianMatrix = typedef Mat

PointChargeList

typedef std::vector< occ::core::PointCharge > occ::qm::PointChargeList

ShellPairList

using occ::qm::ShellPairList = typedef std::vector<std::vector<size_t> >

Enumeration Type Documentation

CoulombMethod

enum class occ::qm::CoulombMethod

strong

Method for computing Coulomb matrix in density fitting.

Enumerator
Traditional	libcint 3-center integrals (default)
SplitRIJ	MMD kernels using Hermite basis (no atomics)

DiisStrategy

enum class occ::qm::DiisStrategy

strong

Strategy for DIIS extrapolation during SCF.

Enumerator
CDIIS	Standard commutator DIIS only.
EDIIS_CDIIS	EDIIS early, switch to CDIIS when error is small.
ADIIS_CDIIS	ADIIS early, switch to CDIIS when error is small (recommended)

DispersionType

enum class occ::qm::DispersionType

strong

Enumerator
None
D4

FittingKind

enum class occ::qm::FittingKind

strong

Enumerator
JK
Correlation

GuessKind

enum class occ::qm::GuessKind

strong

Where the SCF starts from.

Every kind here ends in the same place – diagonalise a Fock matrix built from something cheaper than the answer – and differs only in what that something is. See <occ/qm/initial_guess.h> for how each is built.

This lives apart from the rest of the guess API, and depends on nothing, so that input handling can name a guess without taking on a dependency on the SCF itself.

Enumerator
Auto	Choose per system; see select_guess.
Core	No guess: diagonalise the bare core Hamiltonian. Always available, and always the worst starting point that still converges.
Soad	Superposition of atomic densities: tabulated ground-state occupations spread over a minimal basis, projected into the orbital basis. Cheap and good, but only for elements the shipped minimal basis covers.
Sap	Superposition of atomic potentials: a fitted effective potential per element added to the core Hamiltonian. Covers every element, but has no sound treatment of effective core potentials.
AtomicScf	Superposition of converged isolated-atom densities, one small SCF per element in this calculation's own basis. Costs more than the others and works wherever the orbital basis does, ECPs included.

SpinComponent

enum class occ::qm::SpinComponent

strong

Enumerator
Total
Alpha
Beta

Function Documentation

build_guess()

Guess occ::qm::build_guess	(	GuessKind	kind,
		const GuessRequest &	request
	)

Build kind for request.

Falls back to Core – an empty Guess – when the guess cannot be built for this system, having said why in the log. Every caller therefore gets a usable starting point.

chelpg_charges()

Vec occ::qm::chelpg_charges

(

const Wavefunction &

wfn

)

cosx_nbf_crossover()

int occ::qm::cosx_nbf_crossover

(

)

expectation() [1/2]

template<SpinorbitalKind kind, typename TA >

TA::Scalar occ::qm::expectation	(	const TA &	left,
		const TA &	right
	)

expectation() [2/2]

template<typename TA >

TA::Scalar occ::qm::expectation	(	SpinorbitalKind	sk,
		const TA &	left,
		const TA &	right
	)

from_json()

void occ::qm::from_json	(	const nlohmann::json &	J,
		Energy &	energy
	)

generate_auto_aux()

AutoAuxResult occ::qm::generate_auto_aux	(	const AOBasis &	basis,
		double	threshold = 1e-7,
		std::optional< int >	max_l = std::nullopt
	)

Generate automatic auxiliary basis using pivoted Cholesky decomposition Based on Lehtola, J.

Chem. Theory Comput. 2021, 17, 6886-6900

guess_kind_from_string()

std::optional< GuessKind > occ::qm::guess_kind_from_string ( std::string_view  name )

inline

Parse a guess name. Returns nothing for an unrecognised one.

guess_kind_name()

std::string_view occ::qm::guess_kind_name ( GuessKind  kind )

inline

guess_kind_names()

const std::vector< std::pair< std::string, GuessKind > > & occ::qm::guess_kind_names ( )

inline

The names a user may write, and what each selects.

Shared by the command line and by any other input route, so they cannot drift apart.

matrix_dimensions() [1/2]

template<SpinorbitalKind kind>

constexpr std::pair< size_t, size_t > occ::qm::matrix_dimensions ( size_t  nbf )

constexpr

matrix_dimensions() [2/2]

constexpr std::pair< size_t, size_t > occ::qm::matrix_dimensions ( SpinorbitalKind  kind, size_t  nbf  )

inlineconstexpr

merge_atoms()

std::vector< occ::core::Atom > occ::qm::merge_atoms	(	const std::vector< occ::core::Atom > &	,
		const std::vector< occ::core::Atom > &
	)

merge_basis_sets()

AOBasis occ::qm::merge_basis_sets	(	const AOBasis &	,
		const AOBasis &
	)

merge_molecular_orbitals()

std::pair< Mat, Vec > occ::qm::merge_molecular_orbitals	(	const Mat &	,
		const Mat &	,
		const Vec &	,
		const Vec &	,
		bool	sort_by_energy = false
	)

minimal_basis_covers()

bool occ::qm::minimal_basis_covers

(

const gto::AOBasis &

basis

)

Whether the shipped minimal basis has shells for every atom in basis.

build_sto3g_shells drops elements it has no entry for rather than failing, so loading the minimal basis is not itself a coverage test: an uncovered atom simply comes back carrying no shells.

mulliken_partition()

Vec occ::qm::mulliken_partition	(	const AOBasis &	basis,
		const MolecularOrbitals &	mo,
		Eigen::Ref< const Mat >	op
	)

resolve_fitting_basis()

std::string occ::qm::resolve_fitting_basis	(	const std::string &	orbital_basis_name,
		FittingKind	kind
	)

ScopedRangeSeparation()

template<typename T >

occ::qm::ScopedRangeSeparation	(	T &	,
		double
	)		-> ScopedRangeSeparation< T >

select_guess()

GuessKind occ::qm::select_guess	(	GuessKind	requested,
		const gto::AOBasis &	basis
	)

Resolve Auto into a concrete kind; anything else passes through unchanged, so an explicit request is honoured even where it is a poor choice.

Logs the reason whenever Auto picks something other than SOAD.

shellblock_norm()

template<SpinorbitalKind sk, Shell::Kind kind>

Mat occ::qm::shellblock_norm ( const AOBasis &  basis, const Mat &  matrix  )

inlinenoexcept

supports_incremental_fock_build()

constexpr bool occ::qm::supports_incremental_fock_build ( const FockBuildProperties &  properties )

constexpr

F can only be accumulated when the build is linear and the core Hamiltonian is fixed; screening decides whether it is worth doing.

to_json()

void occ::qm::to_json	(	nlohmann::json &	J,
		const Energy &	energy
	)

Variable Documentation

is_scf_method_v

template<typename T >

constexpr bool occ::qm::is_scf_method_v = SCFMethod<T>

constexpr

supports_density_fitting_v

template<typename T >

constexpr bool occ::qm::supports_density_fitting_v = DensityFittingMethod<T>

constexpr

supports_point_charges_v

template<typename T >

constexpr bool occ::qm::supports_point_charges_v = PointChargeMethod<T>

constexpr