Single-Point Energy — energy()

psi4.energy(name[, molecule, return_wfn, restart_file])[source]

Function to compute the single-point electronic energy.

Returns:float – Total electronic energy in Hartrees. SAPT & EFP return interaction energy.
Returns:(float, Wavefunction) – energy and wavefunction when return_wfn specified.
PSI variables:
Parameters:
  • name (string) –

    'scf' || 'mp2' || 'ci5' || etc.

    First argument, usually unlabeled. Indicates the computational method to be applied to the system.

  • molecule (molecule) –

    h2o || etc.

    The target molecule, if not the last molecule defined.

  • return_wfn (boolean) –

    'on' || \(\Rightarrow\) 'off' \(\Leftarrow\)

    Indicate to additionally return the Wavefunction calculation result as the second element (after float energy) of a tuple.

  • restart_file (string) –

    ['file.1, file.32] || ./file || etc.

    Binary data files to be renamed for calculation restart.
name calls method
efp effective fragment potential (EFP) [manual]
scf Hartree–Fock (HF) or density functional theory (DFT) [manual]
hf HF self consistent field (SCF) [manual]
hf3c HF with dispersion, BSSE, and basis set corrections [manual]
pbeh3c PBEh with dispersion, BSSE, and basis set corrections [manual]
dcft density cumulant functional theory [manual]
mp2 2nd-order Møller–Plesset perturbation theory (MP2) [manual] [details]
mp3 3rd-order Møller–Plesset perturbation theory (MP3) [manual] [details]
fno-mp3 MP3 with frozen natural orbitals [manual]
mp2.5 average of MP2 and MP3 [manual] [details]
mp4(sdq) 4th-order MP perturbation theory (MP4) less triples [manual]
fno-mp4(sdq) MP4 (less triples) with frozen natural orbitals [manual]
mp4 full MP4 [manual] [details]
fno-mp4 full MP4 with frozen natural orbitals [manual]
mpn nth-order Møller–Plesset (MP) perturbation theory [manual]
zaptn nth-order z-averaged perturbation theory (ZAPT) [manual]
omp2 orbital-optimized second-order MP perturbation theory [manual]
scs-omp2 spin-component scaled OMP2 [manual]
scs(n)-omp2 a special version of SCS-OMP2 for nucleobase interactions [manual]
scs-omp2-vdw a special version of SCS-OMP2 (from ethene dimers) [manual]
sos-omp2 spin-opposite scaled OMP2 [manual]
sos-pi-omp2 A special version of SOS-OMP2 for pi systems [manual]
omp3 orbital-optimized third-order MP perturbation theory [manual]
scs-omp3 spin-component scaled OMP3 [manual]
scs(n)-omp3 a special version of SCS-OMP3 for nucleobase interactions [manual]
scs-omp3-vdw a special version of SCS-OMP3 (from ethene dimers) [manual]
sos-omp3 spin-opposite scaled OMP3 [manual]
sos-pi-omp3 A special version of SOS-OMP3 for pi systems [manual]
omp2.5 orbital-optimized MP2.5 [manual]
lccsd, cepa(0) coupled electron pair approximation variant 0 [manual] [details]
fno-lccsd, fno-cepa(0) CEPA(0) with frozen natural orbitals [manual]
cepa(1) coupled electron pair approximation variant 1 [manual]
fno-cepa(1) CEPA(1) with frozen natural orbitals [manual]
cepa(3) coupled electron pair approximation variant 3 [manual]
fno-cepa(3) CEPA(3) with frozen natural orbitals [manual]
acpf averaged coupled-pair functional [manual]
fno-acpf ACPF with frozen natural orbitals [manual]
aqcc averaged quadratic coupled cluster [manual]
fno-aqcc AQCC with frozen natural orbitals [manual]
qcisd quadratic CI singles doubles (QCISD) [manual]
fno-qcisd QCISD with frozen natural orbitals [manual]
lccd Linear CCD [manual] [details]
fno-lccd LCCD with frozen natural orbitals [manual]
olccd orbital optimized LCCD [manual]
cc2 approximate coupled cluster singles and doubles (CC2) [manual]
ccd coupled cluster doubles (CCD) [manual]
ccsd coupled cluster singles and doubles (CCSD) [manual] [details]
bccd Brueckner coupled cluster doubles (BCCD) [manual]
fno-ccsd CCSD with frozen natural orbitals [manual]
qcisd(t) QCISD with perturbative triples [manual]
fno-qcisd(t) QCISD(T) with frozen natural orbitals [manual]
ccsd(t) CCSD with perturbative triples (CCSD(T)) [manual] [details]
ccsd(at) CCSD with asymmetric perturbative triples (CCSD(AT)) [manual] [details]
bccd(t) BCCD with perturbative triples [manual]
fno-ccsd(t) CCSD(T) with frozen natural orbitals [manual]
cc3 approximate CC singles, doubles, and triples (CC3) [manual]
ccenergy expert full control over ccenergy module
dfocc expert full control over dfocc module
cisd configuration interaction (CI) singles and doubles (CISD) [manual] [details]
fno-cisd CISD with frozen natural orbitals [manual]
cisdt CI singles, doubles, and triples (CISDT) [manual]
cisdtq CI singles, doubles, triples, and quadruples (CISDTQ) [manual]
cin nth-order CI [manual]
fci full configuration interaction (FCI) [manual]
detci expert full control over detci module
casscf complete active space self consistent field (CASSCF) [manual]
rasscf restricted active space self consistent field (RASSCF) [manual]
mcscf multiconfigurational self consistent field (SCF) [manual]
psimrcc Mukherjee multireference coupled cluster (Mk-MRCC) [manual]
dmrg-scf density matrix renormalization group SCF [manual]
dmrg-caspt2 density matrix renormalization group CASPT2 [manual]
dmrg-ci density matrix renormalization group CI [manual]
sapt0 0th-order symmetry adapted perturbation theory (SAPT) [manual]
ssapt0 0th-order SAPT with special exchange scaling [manual]
fisapt0 0th-order functional and/or intramolecular SAPT [manual]
sapt2 2nd-order SAPT, traditional definition [manual]
sapt2+ SAPT including all 2nd-order terms [manual]
sapt2+(3) SAPT including perturbative triples [manual]
sapt2+3 SAPT including all 3rd-order terms [manual]
sapt2+(ccd) SAPT2+ with CC-based dispersion [manual]
sapt2+(3)(ccd) SAPT2+(3) with CC-based dispersion [manual]
sapt2+3(ccd) SAPT2+3 with CC-based dispersion [manual]
sapt2+dmp2 SAPT including all 2nd-order terms and MP2 correction [manual]
sapt2+(3)dmp2 SAPT including perturbative triples and MP2 correction [manual]
sapt2+3dmp2 SAPT including all 3rd-order terms and MP2 correction [manual]
sapt2+(ccd)dmp2 SAPT2+ with CC-based dispersion and MP2 correction [manual]
sapt2+(3)(ccd)dmp2 SAPT2+(3) with CC-based dispersion and MP2 correction [manual]
sapt2+3(ccd)dmp2 SAPT2+3 with CC-based dispersion and MP2 correction [manual]
sapt0-ct 0th-order SAPT plus charge transfer (CT) calculation [manual]
sapt2-ct SAPT2 plus CT [manual]
sapt2+-ct SAPT2+ plus CT [manual]
sapt2+(3)-ct SAPT2+(3) plus CT [manual]
sapt2+3-ct SAPT2+3 plus CT [manual]
sapt2+(ccd)-ct SAPT2+(CCD) plus CT [manual]
sapt2+(3)(ccd)-ct SAPT2+(3)(CCD) plus CT [manual]
sapt2+3(ccd)-ct SAPT2+3(CCD) plus CT [manual]
adc 2nd-order algebraic diagrammatic construction (ADC) [manual]
eom-cc2 EOM-CC2 [manual]
eom-ccsd equation of motion (EOM) CCSD [manual]
eom-cc3 EOM-CC3 [manual]
Examples: 
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>>> # [1] Coupled-cluster singles and doubles calculation with psi code
>>> energy('ccsd')

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>>> # [2] Charge-transfer SAPT calculation with scf projection from small into
>>> #     requested basis, with specified projection fitting basis
>>> set basis_guess true
>>> set df_basis_guess jun-cc-pVDZ-JKFIT
>>> energy('sapt0-ct')

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>>> # [3] Arbitrary-order MPn calculation
>>> energy('mp7')

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>>> # [4] Converge scf as singlet, then run detci as triplet upon singlet reference
>>> # Note that the integral transformation is not done automatically when detci is run in a separate step.
>>> molecule H2 {\n0 1\nH\nH 1 0.74\n}
>>> set basis cc-pVDZ
>>> set reference rohf
>>> scf_e, scf_wfn = energy('scf', return_wfn=True)
>>> H2.set_multiplicity(3)
>>> core.MintsHelper(scf_wfn.basisset()).integrals()
>>> energy('detci', ref_wfn=scf_wfn)

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>>> # [5] Run two CI calculations, keeping the integrals generated in the first one.
>>> molecule ne {\nNe\n}
>>> set basis cc-pVDZ
>>> cisd_e, cisd_wfn = energy('cisd', return_wfn=True)
>>> energy('fci', ref_wfn=cisd_wfn)

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>>> # [6] Can automatically perform complete basis set extrapolations
>>> energy("CCSD/cc-pV[DT]Z")

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>>> # [7] Can automatically perform delta corrections that include extrapolations
>>> # even with a user-defined extrapolation formula. See sample inputs named
>>> # cbs-xtpl* for more examples of this input style
>>> energy("MP2/aug-cc-pv([d,t]+d)z + d:ccsd(t)/cc-pvdz", corl_scheme=myxtplfn_2)