pyscf.ci package

Submodules

pyscf.ci.addons module

pyscf.ci.addons.convert_to_gcisd(myci)

pyscf.ci.cisd module

Solve CISD equation H C = C e where e = E_HF + E_CORR

class pyscf.ci.cisd.CISD(mf, frozen=None, mo_coeff=None, mo_occ=None)

Bases: StreamObject

restricted CISD

Attributes:

verboseint

Print level. Default value equals to Mole.verbose

max_memoryfloat or int

Allowed memory in MB. Default value equals to Mole.max_memory

conv_tolfloat

converge threshold. Default is 1e-9.

max_cycleint

max number of iterations. Default is 50.

max_spaceint

Davidson diagonalization space size. Default is 12.

directbool

AO-direct CISD. Default is False.

async_iobool

Allow for asynchronous function execution. Default is True.

frozenint or list

If integer is given, the inner-most orbitals are frozen from CI amplitudes. Given the orbital indices (0-based) in a list, both occupied and virtual orbitals can be frozen in CI calculation.

>>> mol = gto.M(atom = 'H 0 0 0; F 0 0 1.1', basis = 'ccpvdz')
>>> mf = scf.RHF(mol).run()
>>> # freeze 2 core orbitals
>>> myci = ci.CISD(mf).set(frozen = 2).run()
>>> # freeze 2 core orbitals and 3 high lying unoccupied orbitals
>>> myci.set(frozen = [0,1,16,17,18]).run()

Saved results

convergedbool

CISD converged or not

e_corrfloat

CISD correlation correction

e_totfloat

Total CCSD energy (HF + correlation)

ci :

CI wavefunction coefficients

amplitudes_to_cisdvec(c0, c1, c2)

ao2mo(mo_coeff=None)

as_scanner()

Generating a scanner/solver for CISD PES.

The returned solver is a function. This function requires one argument “mol” as input and returns total CISD energy.

The solver will automatically use the results of last calculation as the initial guess of the new calculation. All parameters assigned in the CISD and the underlying SCF objects (conv_tol, max_memory etc) are automatically applied in the solver.

Note scanner has side effects. It may change many underlying objects (_scf, with_df, with_x2c, …) during calculation.

Examples:

>>> from pyscf import gto, scf, ci
>>> mol = gto.M(atom='H 0 0 0; F 0 0 1')
>>> ci_scanner = ci.CISD(scf.RHF(mol)).as_scanner()
>>> e_tot = ci_scanner(gto.M(atom='H 0 0 0; F 0 0 1.1'))
>>> e_tot = ci_scanner(gto.M(atom='H 0 0 0; F 0 0 1.5'))

async_io = True

cisd(ci0=None, eris=None)

cisdvec_to_amplitudes(civec, nmo=None, nocc=None, copy=True)

contract(civec, eris)

Application of CISD hamiltonian onto civec.

Args:

myci : CISD (inheriting) object civec : numpy array, same length as a CI vector. eris : ccsd._ChemistsERIs (inheriting) object (poss diff for df)

Contains the various (pq|rs) integrals needed.

Returns:

numpy array, same length as a CI vector.

conv_tol = 1e-09

density_fit()

direct = False

dump_chk(ci=None, frozen=None, mo_coeff=None, mo_occ=None)

dump_flags(verbose=None)

property e_tot

from_fcivec(fcivec, norb=None, nelec=None)

get_e_hf(mo_coeff=None)

get_frozen_mask()

Get boolean mask for the restricted reference orbitals.

In the returned boolean (mask) array of frozen orbital indices, the element is False if it corresonds to the frozen orbital.

get_init_guess(eris=None, nroots=1, diag=None)

MP2 energy and MP2 initial guess(es) for CISD coefficients.

Kwargs:

erisccsd._ChemistsERIs (inheriting) object (poss diff for df)

Contains the various (pq|rs) integrals needed.

nrootsinteger

Number of CISD solutions to be found.

diagnumpy array (1D)

e.g. CISD Hamiltonian diagonal in Slater determinant space with HF energy subtracted.

Returns:

Tuple of float and numpy array or tuple of float and list of numpy arrays (if nroots > 1) MP2 energy and initial guess(es) for CISD coefficients.

get_nmo()

get_nocc()

kernel(ci0=None, eris=None)

Kernel function is the main driver of a method. Every method should define the kernel function as the entry of the calculation. Note the return value of kernel function is not strictly defined. It can be anything related to the method (such as the energy, the wave-function, the DFT mesh grids etc.).

level_shift = 0.001

lindep = 1e-14

make_diagonal(eris)

Return diagonal of CISD hamiltonian in Slater determinant basis.

Note that a constant has been substracted of all elements. The first element is the HF energy (minus the constant), the next elements are the diagonal elements with singly excited determinants (<D_i^a|H|D_i^a> within the constant), then doubly excited determinants (<D_ij^ab|H|D_ij^ab> within the constant).

Args:

myci : CISD (inheriting) object eris : ccsd._ChemistsERIs (inheriting) object (poss diff for df)

Contains the various (pq|rs) integrals needed.

Returns:

numpy array (size: (1, 1 + #single excitations from HF det

• #double excitations from HF det))

Diagonal elements of hamiltonian matrix within a constant, see above.

make_rdm1(civec=None, nmo=None, nocc=None, ao_repr=False)

Spin-traced one-particle density matrix in MO basis (the occupied-virtual blocks from the orbital response contribution are not included).

dm1[p,q] = <q_alpha^dagger p_alpha> + <q_beta^dagger p_beta>

The convention of 1-pdm is based on McWeeney’s book, Eq (5.4.20). The contraction between 1-particle Hamiltonian and rdm1 is E = einsum(‘pq,qp’, h1, rdm1)

make_rdm2(civec=None, nmo=None, nocc=None, ao_repr=False)

Spin-traced two-particle density matrix in MO basis

dm2[p,q,r,s] = sum_{sigma,tau} <p_sigma^dagger r_tau^dagger s_tau q_sigma>

Note the contraction between ERIs (in Chemist’s notation) and rdm2 is E = einsum(‘pqrs,pqrs’, eri, rdm2)

max_cycle = 50

max_space = 12

property nmo

property nocc

property nstates

nuc_grad_method()

reset(mol=None)

to_fcivec(cisdvec, norb=None, nelec=None, frozen=None)

trans_rdm1(cibra, ciket, nmo=None, nocc=None)

Spin-traced one-particle transition density matrix in MO basis.

dm1[p,q] = <q_alpha^dagger p_alpha> + <q_beta^dagger p_beta>

The convention of 1-pdm is based on McWeeney’s book, Eq (5.4.20). The contraction between 1-particle Hamiltonian and rdm1 is E = einsum(‘pq,qp’, h1, rdm1)

vector_size()

The size of the vector which was returned from amplitudes_to_cisdvec()

class pyscf.ci.cisd.CISD_Scanner(ci)

Bases: SinglePointScanner

class pyscf.ci.cisd.RCISD(mf, frozen=None, mo_coeff=None, mo_occ=None)

Bases: CISD

pyscf.ci.cisd.amplitudes_to_cisdvec(c0, c1, c2)

pyscf.ci.cisd.as_scanner(ci)

Generating a scanner/solver for CISD PES.

The returned solver is a function. This function requires one argument “mol” as input and returns total CISD energy.

The solver will automatically use the results of last calculation as the initial guess of the new calculation. All parameters assigned in the CISD and the underlying SCF objects (conv_tol, max_memory etc) are automatically applied in the solver.

Note scanner has side effects. It may change many underlying objects (_scf, with_df, with_x2c, …) during calculation.

Examples:

>>> from pyscf import gto, scf, ci
>>> mol = gto.M(atom='H 0 0 0; F 0 0 1')
>>> ci_scanner = ci.CISD(scf.RHF(mol)).as_scanner()
>>> e_tot = ci_scanner(gto.M(atom='H 0 0 0; F 0 0 1.1'))
>>> e_tot = ci_scanner(gto.M(atom='H 0 0 0; F 0 0 1.5'))

pyscf.ci.cisd.cisdvec_to_amplitudes(civec, nmo, nocc, copy=True)

pyscf.ci.cisd.contract(myci, civec, eris)

Application of CISD hamiltonian onto civec.

Args:

myci : CISD (inheriting) object civec : numpy array, same length as a CI vector. eris : ccsd._ChemistsERIs (inheriting) object (poss diff for df)

Contains the various (pq|rs) integrals needed.

Returns:

numpy array, same length as a CI vector.

pyscf.ci.cisd.dot(v1, v2, nmo, nocc)

pyscf.ci.cisd.from_fcivec(ci0, norb, nelec, frozen=None)

Extract CISD coefficients from FCI coefficients

pyscf.ci.cisd.kernel(myci, eris, ci0=None, max_cycle=50, tol=1e-08, verbose=4)

Run CISD calculation.

Args:

myci : CISD (inheriting) object eris : ccsd._ChemistsERIs (inheriting) object (poss diff for df)

Contains the various (pq|rs) integrals needed.

Kwargs:

ci0(List of) numpy array(s) (if None it will set)

Initial guess for CISD coeffs.

max_cycleinteger

Maximum number of iterations to converge to CISD solution. If not converged before, calculation stops without having converged.

tolfloat

Convergence tolerance.

verboseinteger

Level of output (roughly: the higher, the more output).

Returns:

convbool

Is it converged?

ecisdList of floats or float

The lowest myci.nroots eigenvalues.

ciList of 1D arrays or 1D array

The lowest myci.nroots eigenvectors.

pyscf.ci.cisd.make_diagonal(myci, eris)

Return diagonal of CISD hamiltonian in Slater determinant basis.

Note that a constant has been substracted of all elements. The first element is the HF energy (minus the constant), the next elements are the diagonal elements with singly excited determinants (<D_i^a|H|D_i^a> within the constant), then doubly excited determinants (<D_ij^ab|H|D_ij^ab> within the constant).

Args:

myci : CISD (inheriting) object eris : ccsd._ChemistsERIs (inheriting) object (poss diff for df)

Contains the various (pq|rs) integrals needed.

Returns:

numpy array (size: (1, 1 + #single excitations from HF det

• #double excitations from HF det))

Diagonal elements of hamiltonian matrix within a constant, see above.

pyscf.ci.cisd.make_rdm1(myci, civec=None, nmo=None, nocc=None, ao_repr=False)

Spin-traced one-particle density matrix in MO basis (the occupied-virtual blocks from the orbital response contribution are not included).

dm1[p,q] = <q_alpha^dagger p_alpha> + <q_beta^dagger p_beta>

The convention of 1-pdm is based on McWeeney’s book, Eq (5.4.20). The contraction between 1-particle Hamiltonian and rdm1 is E = einsum(‘pq,qp’, h1, rdm1)

pyscf.ci.cisd.make_rdm2(myci, civec=None, nmo=None, nocc=None, ao_repr=False)

Spin-traced two-particle density matrix in MO basis

dm2[p,q,r,s] = sum_{sigma,tau} <p_sigma^dagger r_tau^dagger s_tau q_sigma>

Note the contraction between ERIs (in Chemist’s notation) and rdm2 is E = einsum(‘pqrs,pqrs’, eri, rdm2)

pyscf.ci.cisd.overlap(cibra, ciket, nmo, nocc, s=None)

Overlap between two CISD wavefunctions.

Args:

s2D array

The overlap matrix of non-orthogonal one-particle basis

pyscf.ci.cisd.t1strs(norb, nelec)

Compute the FCI strings (address) for CIS single-excitation amplitudes and the signs of the coefficients when transferring the reference from physics vacuum to HF vacuum.

pyscf.ci.cisd.tn_addrs_signs(norb, nelec, n_excite)

Compute the FCI strings (address) for CIS n-excitation amplitudes and the signs of the coefficients when transferring the reference from physics vacuum to HF vacuum.

If the excitation level is not compatible with the number of electrons and holes, empty lists are returned for the addresses and signs.

pyscf.ci.cisd.to_fcivec(cisdvec, norb, nelec, frozen=None)

Convert CISD coefficients to FCI coefficients

pyscf.ci.cisd.trans_rdm1(myci, cibra, ciket, nmo=None, nocc=None)

Spin-traced one-particle transition density matrix in MO basis.

dm1[p,q] = <q_alpha^dagger p_alpha> + <q_beta^dagger p_beta>

The convention of 1-pdm is based on McWeeney’s book, Eq (5.4.20). The contraction between 1-particle Hamiltonian and rdm1 is E = einsum(‘pq,qp’, h1, rdm1)

pyscf.ci.gcisd module

General spin-orbital CISD

pyscf.ci.gcisd.CISD

alias of GCISD

class pyscf.ci.gcisd.GCISD(mf, frozen=None, mo_coeff=None, mo_occ=None)

Bases: CISD

amplitudes_to_cisdvec(c0, c1, c2)

ao2mo(mo_coeff=None)

cisdvec_to_amplitudes(civec, nmo=None, nocc=None, copy=True)

contract(civec, eris)

Application of CISD hamiltonian onto civec.

Args:

myci : CISD (inheriting) object civec : numpy array, same length as a CI vector. eris : ccsd._ChemistsERIs (inheriting) object (poss diff for df)

Contains the various (pq|rs) integrals needed.

Returns:

numpy array, same length as a CI vector.

from_fcivec(fcivec, nelec, orbspin, frozen=None)

from_rcisdvec(civec, nocc=None, orbspin=None)

Convert the (spin-separated) CISD coefficient vector to GCISD coefficient vector

from_ucisdvec(civec, nocc=None, orbspin=None)

Convert the (spin-separated) CISD coefficient vector to GCISD coefficient vector

get_init_guess(eris=None, nroots=1, diag=None)

MP2 energy and MP2 initial guess(es) for CISD coefficients.

Kwargs:

erisccsd._ChemistsERIs (inheriting) object (poss diff for df)

Contains the various (pq|rs) integrals needed.

nrootsinteger

Number of CISD solutions to be found.

diagnumpy array (1D)

e.g. CISD Hamiltonian diagonal in Slater determinant space with HF energy subtracted.

Returns:

Tuple of float and numpy array or tuple of float and list of numpy arrays (if nroots > 1) MP2 energy and initial guess(es) for CISD coefficients.

make_diagonal(eris)

Return diagonal of CISD hamiltonian in Slater determinant basis.

Note that a constant has been substracted of all elements. The first element is the HF energy (minus the constant), the next elements are the diagonal elements with singly excited determinants (<D_i^a|H|D_i^a> within the constant), then doubly excited determinants (<D_ij^ab|H|D_ij^ab> within the constant).

Args:

myci : CISD (inheriting) object eris : ccsd._ChemistsERIs (inheriting) object (poss diff for df)

Contains the various (pq|rs) integrals needed.

Returns:

numpy array (size: (1, 1 + #single excitations from HF det

• #double excitations from HF det))

Diagonal elements of hamiltonian matrix within a constant, see above.

make_rdm1(civec=None, nmo=None, nocc=None, ao_repr=False)

One-particle density matrix in the molecular spin-orbital representation (the occupied-virtual blocks from the orbital response contribution are not included).

dm1[p,q] = <q^dagger p> (p,q are spin-orbitals)

The convention of 1-pdm is based on McWeeney’s book, Eq (5.4.20). The contraction between 1-particle Hamiltonian and rdm1 is E = einsum(‘pq,qp’, h1, rdm1)

make_rdm2(civec=None, nmo=None, nocc=None, ao_repr=False)

Two-particle density matrix in the molecular spin-orbital representation

dm2[p,q,r,s] = <p^dagger r^dagger s q>

where p,q,r,s are spin-orbitals. p,q correspond to one particle and r,s correspond to another particle. The contraction between ERIs (in Chemist’s notation) and rdm2 is E = einsum(‘pqrs,pqrs’, eri, rdm2)

spatial2spin(tx, orbspin=None)

spin2spatial(tx, orbspin=None)

to_fcivec(cisdvec, nelec, orbspin, frozen=None)

to_ucisdvec(civec, orbspin=None)

Convert the GCISD coefficient vector to UCISD coefficient vector

trans_rdm1(cibra, ciket, nmo=None, nocc=None)

One-particle transition density matrix in the molecular spin-orbital representation.

dm1[p,q] = <q^dagger p> (p,q are spin-orbitals)

The convention of 1-pdm is based on McWeeney’s book, Eq (5.4.20). The contraction between 1-particle Hamiltonian and rdm1 is E = einsum(‘pq,qp’, h1, rdm1)

vector_size()

The size of the vector which was returned from amplitudes_to_cisdvec()

pyscf.ci.gcisd.amplitudes_to_cisdvec(c0, c1, c2)

pyscf.ci.gcisd.cisdvec_to_amplitudes(civec, nmo, nocc, copy=True)

pyscf.ci.gcisd.contract(myci, civec, eris)

pyscf.ci.gcisd.from_fcivec(ci0, nelec, orbspin, frozen=None)

pyscf.ci.gcisd.from_rcisdvec(civec, nocc, orbspin)

Convert the (spin-separated) CISD coefficient vector to GCISD coefficient vector

pyscf.ci.gcisd.from_ucisdvec(civec, nocc, orbspin)

Convert the (spin-separated) CISD coefficient vector to GCISD coefficient vector

pyscf.ci.gcisd.make_diagonal(myci, eris)

pyscf.ci.gcisd.make_rdm1(myci, civec=None, nmo=None, nocc=None, ao_repr=False)

One-particle density matrix in the molecular spin-orbital representation (the occupied-virtual blocks from the orbital response contribution are not included).

dm1[p,q] = <q^dagger p> (p,q are spin-orbitals)

The convention of 1-pdm is based on McWeeney’s book, Eq (5.4.20). The contraction between 1-particle Hamiltonian and rdm1 is E = einsum(‘pq,qp’, h1, rdm1)

pyscf.ci.gcisd.make_rdm2(myci, civec=None, nmo=None, nocc=None, ao_repr=False)

Two-particle density matrix in the molecular spin-orbital representation

dm2[p,q,r,s] = <p^dagger r^dagger s q>

where p,q,r,s are spin-orbitals. p,q correspond to one particle and r,s correspond to another particle. The contraction between ERIs (in Chemist’s notation) and rdm2 is E = einsum(‘pqrs,pqrs’, eri, rdm2)

pyscf.ci.gcisd.to_fcivec(cisdvec, nelec, orbspin, frozen=None)

pyscf.ci.gcisd.to_ucisdvec(civec, nmo, nocc, orbspin)

Convert the GCISD coefficient vector to UCISD coefficient vector

pyscf.ci.gcisd.trans_rdm1(myci, cibra, ciket, nmo=None, nocc=None)

One-particle transition density matrix in the molecular spin-orbital representation.

dm1[p,q] = <q^dagger p> (p,q are spin-orbitals)

The convention of 1-pdm is based on McWeeney’s book, Eq (5.4.20). The contraction between 1-particle Hamiltonian and rdm1 is E = einsum(‘pq,qp’, h1, rdm1)

pyscf.ci.ucisd module

Unrestricted CISD

pyscf.ci.ucisd.CISD

alias of UCISD

class pyscf.ci.ucisd.UCISD(mf, frozen=None, mo_coeff=None, mo_occ=None)

Bases: CISD

amplitudes_to_cisdvec(c0, c1, c2)

ao2mo(mo_coeff=None)

cisdvec_to_amplitudes(civec, nmo=None, nocc=None, copy=True)

contract(civec, eris)

Application of CISD hamiltonian onto civec.

Args:

myci : CISD (inheriting) object civec : numpy array, same length as a CI vector. eris : ccsd._ChemistsERIs (inheriting) object (poss diff for df)

Contains the various (pq|rs) integrals needed.

Returns:

numpy array, same length as a CI vector.

from_fcivec(fcivec, nmo=None, nocc=None)

get_frozen_mask()

Get boolean mask for the unrestricted reference orbitals.

In the returned boolean (mask) array of frozen orbital indices, the element is False if it corresonds to the frozen orbital.

get_init_guess(eris=None, nroots=1, diag=None)

MP2 energy and MP2 initial guess(es) for CISD coefficients.

Kwargs:

erisccsd._ChemistsERIs (inheriting) object (poss diff for df)

Contains the various (pq|rs) integrals needed.

nrootsinteger

Number of CISD solutions to be found.

diagnumpy array (1D)

e.g. CISD Hamiltonian diagonal in Slater determinant space with HF energy subtracted.

Returns:

Tuple of float and numpy array or tuple of float and list of numpy arrays (if nroots > 1) MP2 energy and initial guess(es) for CISD coefficients.

get_nmo()

get_nocc()

make_diagonal(eris)

Return diagonal of CISD hamiltonian in Slater determinant basis.

Note that a constant has been substracted of all elements. The first element is the HF energy (minus the constant), the next elements are the diagonal elements with singly excited determinants (<D_i^a|H|D_i^a> within the constant), then doubly excited determinants (<D_ij^ab|H|D_ij^ab> within the constant).

Args:

myci : CISD (inheriting) object eris : ccsd._ChemistsERIs (inheriting) object (poss diff for df)

Contains the various (pq|rs) integrals needed.

Returns:

numpy array (size: (1, 1 + #single excitations from HF det

• #double excitations from HF det))

Diagonal elements of hamiltonian matrix within a constant, see above.

make_rdm1(civec=None, nmo=None, nocc=None, ao_repr=False)

One-particle spin density matrices dm1a, dm1b in MO basis (the occupied-virtual blocks due to the orbital response contribution are not included).

dm1a[p,q] = <q_alpha^dagger p_alpha> dm1b[p,q] = <q_beta^dagger p_beta>

The convention of 1-pdm is based on McWeeney’s book, Eq (5.4.20).

make_rdm2(civec=None, nmo=None, nocc=None, ao_repr=False)

Two-particle spin density matrices dm2aa, dm2ab, dm2bb in MO basis

dm2aa[p,q,r,s] = <q_alpha^dagger s_alpha^dagger r_alpha p_alpha> dm2ab[p,q,r,s] = <q_alpha^dagger s_beta^dagger r_beta p_alpha> dm2bb[p,q,r,s] = <q_beta^dagger s_beta^dagger r_beta p_beta>

(p,q correspond to one particle and r,s correspond to another particle) Two-particle density matrix should be contracted to integrals with the pattern below to compute energy

E = numpy.einsum(‘pqrs,pqrs’, eri_aa, dm2_aa) E+= numpy.einsum(‘pqrs,pqrs’, eri_ab, dm2_ab) E+= numpy.einsum(‘pqrs,rspq’, eri_ba, dm2_ab) E+= numpy.einsum(‘pqrs,pqrs’, eri_bb, dm2_bb)

where eri_aa[p,q,r,s] = (p_alpha q_alpha | r_alpha s_alpha ) eri_ab[p,q,r,s] = ( p_alpha q_alpha | r_beta s_beta ) eri_ba[p,q,r,s] = ( p_beta q_beta | r_alpha s_alpha ) eri_bb[p,q,r,s] = ( p_beta q_beta | r_beta s_beta )

nuc_grad_method()

to_fcivec(cisdvec, nmo=None, nocc=None)

trans_rdm1(cibra, ciket, nmo=None, nocc=None)

One-particle spin density matrices dm1a, dm1b in MO basis (the occupied-virtual blocks due to the orbital response contribution are not included).

dm1a[p,q] = <q_alpha^dagger p_alpha> dm1b[p,q] = <q_beta^dagger p_beta>

The convention of 1-pdm is based on McWeeney’s book, Eq (5.4.20).

vector_size()

The size of the vector which was returned from amplitudes_to_cisdvec()

pyscf.ci.ucisd.amplitudes_to_cisdvec(c0, c1, c2)

pyscf.ci.ucisd.cisdvec_to_amplitudes(civec, nmo, nocc, copy=True)

pyscf.ci.ucisd.contract(myci, civec, eris)

pyscf.ci.ucisd.from_fcivec(ci0, norb, nelec, frozen=None)

Extract CISD coefficients from FCI coefficients

pyscf.ci.ucisd.make_diagonal(myci, eris)

pyscf.ci.ucisd.make_rdm1(myci, civec=None, nmo=None, nocc=None, ao_repr=False)

One-particle spin density matrices dm1a, dm1b in MO basis (the occupied-virtual blocks due to the orbital response contribution are not included).

dm1a[p,q] = <q_alpha^dagger p_alpha> dm1b[p,q] = <q_beta^dagger p_beta>

The convention of 1-pdm is based on McWeeney’s book, Eq (5.4.20).

pyscf.ci.ucisd.make_rdm2(myci, civec=None, nmo=None, nocc=None, ao_repr=False)

Two-particle spin density matrices dm2aa, dm2ab, dm2bb in MO basis

dm2aa[p,q,r,s] = <q_alpha^dagger s_alpha^dagger r_alpha p_alpha> dm2ab[p,q,r,s] = <q_alpha^dagger s_beta^dagger r_beta p_alpha> dm2bb[p,q,r,s] = <q_beta^dagger s_beta^dagger r_beta p_beta>

(p,q correspond to one particle and r,s correspond to another particle) Two-particle density matrix should be contracted to integrals with the pattern below to compute energy

E = numpy.einsum(‘pqrs,pqrs’, eri_aa, dm2_aa) E+= numpy.einsum(‘pqrs,pqrs’, eri_ab, dm2_ab) E+= numpy.einsum(‘pqrs,rspq’, eri_ba, dm2_ab) E+= numpy.einsum(‘pqrs,pqrs’, eri_bb, dm2_bb)

where eri_aa[p,q,r,s] = (p_alpha q_alpha | r_alpha s_alpha ) eri_ab[p,q,r,s] = ( p_alpha q_alpha | r_beta s_beta ) eri_ba[p,q,r,s] = ( p_beta q_beta | r_alpha s_alpha ) eri_bb[p,q,r,s] = ( p_beta q_beta | r_beta s_beta )

pyscf.ci.ucisd.overlap(cibra, ciket, nmo, nocc, s=None)

Overlap between two CISD wavefunctions.

Args:

sa list of 2D arrays

The overlap matrix of non-orthogonal one-particle basis

pyscf.ci.ucisd.to_fcivec(cisdvec, norb, nelec, frozen=None)

Convert CISD coefficients to FCI coefficients

pyscf.ci.ucisd.trans_rdm1(myci, cibra, ciket, nmo=None, nocc=None)

One-particle spin density matrices dm1a, dm1b in MO basis (the occupied-virtual blocks due to the orbital response contribution are not included).

dm1a[p,q] = <q_alpha^dagger p_alpha> dm1b[p,q] = <q_beta^dagger p_beta>

The convention of 1-pdm is based on McWeeney’s book, Eq (5.4.20).

Module contents

pyscf.ci.CISD(mf, frozen=None, mo_coeff=None, mo_occ=None)

restricted CISD

Attributes:

verboseint

Print level. Default value equals to Mole.verbose

max_memoryfloat or int

Allowed memory in MB. Default value equals to Mole.max_memory

conv_tolfloat

converge threshold. Default is 1e-9.

max_cycleint

max number of iterations. Default is 50.

max_spaceint

Davidson diagonalization space size. Default is 12.

directbool

AO-direct CISD. Default is False.

async_iobool

Allow for asynchronous function execution. Default is True.

frozenint or list

If integer is given, the inner-most orbitals are frozen from CI amplitudes. Given the orbital indices (0-based) in a list, both occupied and virtual orbitals can be frozen in CI calculation.

>>> mol = gto.M(atom = 'H 0 0 0; F 0 0 1.1', basis = 'ccpvdz')
>>> mf = scf.RHF(mol).run()
>>> # freeze 2 core orbitals
>>> myci = ci.CISD(mf).set(frozen = 2).run()
>>> # freeze 2 core orbitals and 3 high lying unoccupied orbitals
>>> myci.set(frozen = [0,1,16,17,18]).run()

Saved results

convergedbool

CISD converged or not

e_corrfloat

CISD correlation correction

e_totfloat

Total CCSD energy (HF + correlation)

ci :

CI wavefunction coefficients

pyscf.ci.GCISD(mf, frozen=None, mo_coeff=None, mo_occ=None)

pyscf.ci.QCISD(mf, frozen=None, mo_coeff=None, mo_occ=None)

restricted QCISD

pyscf.ci.RCISD(mf, frozen=None, mo_coeff=None, mo_occ=None)

pyscf.ci.RQCISD(mf, frozen=None, mo_coeff=None, mo_occ=None)

restricted QCISD

pyscf.ci.UCISD(mf, frozen=None, mo_coeff=None, mo_occ=None)