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.
Examples: 
>>> # [1] Coupled-cluster singles and doubles calculation with psi code
>>> energy('ccsd')

>>> # [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')

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

>>> # [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)

>>> # [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)

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

>>> # [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)