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# Energy

`energy`(name[, bypass_scf, molecule])

  Function to compute the single-point electronic energy.

  Returns: | (float) Total electronic energy in Hartrees. SAPT returns interaction energy.
  PSI variables: |

  - `CURRENT ENERGY`
  - `CURRENT REFERENCE ENERGY`
  - `CURRENT CORRELATION ENERGY`

  name | calls method
  --- | ---
  scf | Hartree–Fock (HF) or density functional theory (DFT) [manual]
  dcft | density cumulant functional theory [manual]
  mcscf | multiconfigurational self consistent field (SCF)
  mp2 | 2nd-order Moller-Plesset perturbation theory (MP2) [manual]
  df-mp2 | MP2 with density fitting [manual]
  conv-mp2 | conventional MP2 (non-density-fitting) [manual]
  mp3 | 3rd-order Moller-Plesset perturbation theory (MP3) [manual]
  mp2.5 | average of MP2 and MP3 [manual]
  mp4(sdq) | 4th-order MP perturbation theory (MP4) less triples [manual]
  mp4 | full MP4 [manual]
  mpn | nth-order Moller–Plesset (MP) perturbation theory [manual]
  zaptn | nth-order z-averaged perturbation theory (ZAPT) [manual]
  omp2 | orbital-optimized second-order MP perturbation theory [manual]
  omp3 | orbital-optimized third-order MP perturbation theory [manual]
  omp2.5 | orbital-optimized MP2.5 [manual]
  ocepa | orbital-optimized coupled electron pair approximation [manual]
  cepa0 | coupled electron pair approximation, equiv. linear. CCD [manual]
  cepa(0) | coupled electron pair approximation variant 0 [manual]
  cepa(1) | coupled electron pair approximation variant 1 [manual]
  cepa(3) | coupled electron pair approximation variant 3 [manual]
  acpf | averaged coupled-pair functional [manual]
  aqcc | averaged quadratic coupled cluster [manual]
  qcisd | quadratic CI singles doubles (QCISD) [manual]
  cc2 | approximate coupled cluster singles and doubles (CC2) [manual]
  ccsd | coupled cluster singles and doubles (CCSD) [manual]
  bccd | Brueckner coupled cluster doubles (BCCD) [manual]
  qcisd(t) | QCISD with perturbative triples [manual]
  ccsd(t) | CCSD with perturbative triples (CCSD(T)) [manual]
  fno-df-ccsd(t) | CCSD(T) with density fitting and frozen natural orbitals [manual]
  bccd(t) | BCCD with perturbative triples [manual]
  cc3 | approximate CC singles, doubles, and triples (CC3) [manual]
  ccenergy | expert full control over ccenergy module
  cisd | configuration interaction (CI) singles and doubles (CISD) [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
  gaussian-2 (g2) | gaussian-2 composite method [manual]
  sapt0 | 0th-order symmetry adapted perturbation theory (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]
  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]

  name | calls method (aliases to name = ‘scf’)
  --- | ---
  hf | HF
  rhf | HF with restricted reference
  uhf | HF with unrestricted reference
  rohf | HF with restricted open-shell reference
  rscf | HF or DFT with restricted reference
  uscf | HF or DFT with unrestricted reference
  roscf | HF or DFT with restricted open-shell reference

  name | calls method DFT [manual]
  --- | ---
  b2plyp | B2PLYP Double Hybrid Exchange-Correlation Functional
  b2plyp-d | B2PLYP Double Hybrid Exchange-Correlation Functional w/ Grimme’s -D2 Dispersion Correction
  b2plyp-d3 | B2PLYP Double Hybrid Exchange-Correlation Functional w/ Grimme’s -D3 (zero-damping) Dispersion Correction
  b2plyp-d3bj | B2PLYP Double Hybrid Exchange-Correlation Functional w/ Grimme’s -D3 (BJ-damping) Dispersion Correction
  b3lyp | B3LYP Hybrid-GGA Exchange-Correlation Functional
  b3lyp-chg | B3LYP Hybrid-GGA Exchange-Correlation Functional w/ Chai and Head-Gordon Dispersion Correction
  b3lyp-d | B3LYP Hybrid-GGA Exchange-Correlation Functional w/ Grimme’s -D2 Dispersion Correction
  b3lyp-d1 | B3LYP Hybrid-GGA Exchange-Correlation Functional w/ Grimme’s -D1 Dispersion Correction
  b3lyp-d3 | B3LYP Hybrid-GGA Exchange-Correlation Functional w/ Grimme’s -D3 (zero-damping) Dispersion Correction
  b3lyp-d3bj | B3LYP Hybrid-GGA Exchange-Correlation Functional w/ Grimme’s -D3 (BJ-damping) Dispersion Correction
  b3_x | Becke88 GGA Exchange (B3LYP weighting)
  b88_x | Becke88 GGA Exchange
  b97-0 | B97-0 Hybrid-GGA Exchange-Correlation Functional
  b97-1 | B97-1 Hybrid-GGA Exchange-Correlation Functional
  b97-2 | B97-2 Hybrid-GGA Exchange-Correlation Functional
  b97-d | B97-D Pure-GGA Exchange-Correlation Functional w/ Grimme’s -D2 Dispersion Correction
  b97-d3 | B97-D Pure-GGA Exchange-Correlation Functional w/ Grimme’s -D3 (zero-damping) Dispersion Correction
  b97-d3bj | B97-D Pure-GGA Exchange-Correlation Functional w/ Grimme’s -D3 (BJ-damping) Dispersion Correction
  blyp | BLYP GGA Exchange-Correlation Functional
  blyp-d | BLYP GGA Exchange-Correlation Functional w/ Grimme’s -D2 Dispersion Correction
  blyp-d1 | B3LYP Hybrid-GGA Exchange-Correlation Functional w/ Grimme’s -D1 Dispersion Correction
  blyp-d3 | BLYP GGA Exchange-Correlation Functional w/ Grimme’s -D3 (zero-damping) Dispersion Correction
  blyp-d3bj | BLYP GGA Exchange-Correlation Functional w/ Grimme’s -D3 (BJ-damping) Dispersion Correction
  bp86 | BP86 GGA Exchange-Correlation Functional
  bp86-d | BP86 GGA Exchange-Correlation Functional w/ Grimme’s -D2 Dispersion Correction
  bp86-d1 | B3LYP Hybrid-GGA Exchange-Correlation Functional w/ Grimme’s -D1 Dispersion Correction
  bp86-d3 | BP86 GGA Exchange-Correlation Functional w/ Grimme’s -D3 (zero-damping) Dispersion Correction
  bp86-d3bj | BP86 GGA Exchange-Correlation Functional w/ Grimme’s -D3 (BJ-damping) Dispersion Correction
  dsd-blyp | DSD-BLYP Dispersion-corrected SCS Double Hybrid XC Functional w/ Grimme’s -D2 Dispersion Correction
  dsd-pbep86 | DSD-PBEP86 Dispersion-corrected SCS Double Hybrid XC Functional (opt. for -D2) w/ Grimme’s -D2 Dispersion Correction
  dsd-pbepbe | DSD-PBEPBE Dispersion-corrected SCS Double Hybrid XC Functional w/ Grimme’s -D2 Dispersion Correction
  ft97 | FT97 GGA Exchange-Correlation Functional
  ft97b_x | Filitov and Theil 1997 Exchange
  ft97_c | FT97 Correlation (Involves Ei functions)
  hcth | HCTH Pure-GGA Exchange-Correlation Functional
  hcth120 | HCTH120 Pure-GGA Exchange-Correlation Functional
  hcth120-d3 | HCTH120 Pure-GGA Exchange-Correlation Functional w/ Grimme’s -D3 (zero-damping) Dispersion Correction
  hcth120-d3bj | HCTH120 Pure-GGA Exchange-Correlation Functional w/ Grimme’s -D3 (BJ-damping) Dispersion Correction
  hcth147 | HCTH147 Pure-GGA Exchange-Correlation Functional
  hcth407 | HCTH407 Pure-GGA Exchange-Correlation Functional
  hf+d | w/ Podeszwa and Szalewicz Dispersion Correction
  lyp_c | LYP Correlation
  m05 | Heavily Parameterized Hybrid Meta-GGA XC Functional
  m05-2x | Heavily Parameterized Hybrid Meta-GGA XC Functional
  m05-2x-d3 | Heavily Parameterized Hybrid Meta-GGA XC Functional w/ Grimme’s -D3 (zero-damping) Dispersion Correction
  m05-d3 | Heavily Parameterized Hybrid Meta-GGA XC Functional w/ Grimme’s -D3 (zero-damping) Dispersion Correction
  p86_c | P86 Correlation (PZ81 LSDA + P86 GGA)
  pbe | PBE GGA Exchange-Correlation Functional
  pbe-d | PBE GGA Exchange-Correlation Functional w/ Grimme’s -D2 Dispersion Correction
  pbe-d1 | PBE GGA Exchange-Correlation Functional w/ Grimme’s -D1 Dispersion Correction
  pbe-d3 | PBE GGA Exchange-Correlation Functional w/ Grimme’s -D3 (zero-damping) Dispersion Correction
  pbe-d3bj | PBE GGA Exchange-Correlation Functional w/ Grimme’s -D3 (BJ-damping) Dispersion Correction
  pbe0 | PBE0 Hybrid GGA Exchange-Correlation Functional
  pbe0-2 | PBE0-2 Double Hydrid Exchange-Correlation Functional
  pbe0-d | PBE0 Hybrid GGA Exchange-Correlation Functional w/ Grimme’s -D2 Dispersion Correction
  pbe0-d3 | PBE0 Hybrid GGA Exchange-Correlation Functional w/ Grimme’s -D3 (zero-damping) Dispersion Correction
  pbe0-d3bj | PBE0 Hybrid GGA Exchange-Correlation Functional w/ Grimme’s -D3 (BJ-damping) Dispersion Correction
  pbesol_x | PBEsol GGA Exchange Hole (Parameter Free)
  pbe_c | PBE Correlation
  pbe_x | PBE GGA Exchange Hole (Parameter Free)
  pw91 | PW91 GGA Exchange-Correlation Functional
  pw91_c | PW91 Correlation
  pw91_x | PW91 Parameterized GGA Exchange
  pw92_c |
  pz81_c | PZ81 Correlation
  rpbe_x | RPBE GGA Exchange Hole (Parameter Free)
  sogga | Second Order GGA Exchange-Correlation Functional
  sogga_x | Second Order GGA Exchange Hole (Parameter Free)
  svwn | SVWN3 (RPA) LSDA Functional
  s_x | Slater LSDA Exchange
  vwn3rpa_c | VWN3 (RPA) LSDA Correlation
  vwn3_c | VWN3 LSDA Correlation
  vwn5rpa_c | VWN5 (RPA) LSDA Correlation
  vwn5_c | VWN5 LSDA Correlation
  dldf | Dispersionless Hybrid Meta-GGA XC Functional
  dldf+d | Dispersionless Hybrid Meta-GGA XC Functional w/ Podeszwa and Szalewicz Dispersion Correction
  dldf+d09 | Dispersionless Hybrid Meta-GGA XC Functional w/ Podeszwa and Szalewicz Dispersion Correction
  wb88_x | B88 Short-Range GGA Exchange (HJS Model)
  wb97 | Parameterized LRC B97 GGA XC Functional
  wb97x | Parameterized Hybrid LRC B97 GGA XC Functional
  wb97x-2(lp) | Double Hybrid LRC B97 GGA XC Functional (Large Pople parametrization)
  wb97x-2(tqz) | Double Hybrid LRC B97 GGA XC Functional (TQZ parametrization)
  wb97x-d | Parameterized Hybrid LRC B97 GGA XC Functional with Dispersion w/ Chai and Head-Gordon Dispersion Correction
  wblyp | BLYP SR-XC Functional (HJS Model)
  wpbe | PBE SR-XC Functional (HJS Model)
  wpbe0 | PBE0 SR-XC Functional (HJS Model)
  wpbe_x | PBE Short-Range GGA Exchange (HJS Model)
  wpbesol | PBEsol SR-XC Functional (HJS Model)
  wpbesol0 | PBEsol0 SR-XC Functional (HJS Model)
  wpbesol_x | PBEsol Short-Range GGA Exchange (HJS Model)
  wsvwn | LSDA SR-XC Functional
  ws_x | Slater Short-Range LSDA Exchange

  name | calls method in Kallay’s MRCC program [manual]
  --- | ---
  mrccsd | CC through doubles
  mrccsdt | CC through triples
  mrccsdtq | CC through quadruples
  mrccsdtqp | CC through quintuples
  mrccsdtqph | CC through sextuples
  mrccsd(t) | CC through doubles with perturbative triples
  mrccsdt(q) | CC through triples with perturbative quadruples
  mrccsdtq(p) | CC through quadruples with pertubative quintuples
  mrccsdtqp(h) | CC through quintuples with pertubative sextuples
  mrccsd(t)_l |
  mrccsdt(q)_l |
  mrccsdtq(p)_l |
  mrccsdtqp(h)_l |
  mrccsdt-1a | CC through doubles with iterative triples (cheapest terms)
  mrccsdtq-1a | CC through triples with iterative quadruples (cheapest terms)
  mrccsdtqp-1a | CC through quadruples with iterative quintuples (cheapest terms)
  mrccsdtqph-1a | CC through quintuples with iterative sextuples (cheapest terms)
  mrccsdt-1b | CC through doubles with iterative triples (cheaper terms)
  mrccsdtq-1b | CC through triples with iterative quadruples (cheaper terms)
  mrccsdtqp-1b | CC through quadruples with iterative quintuples (cheaper terms)
  mrccsdtqph-1b | CC through quintuples with iterative sextuples (cheaper terms)
  mrcc2 | approximate CC through doubles
  mrcc3 | approximate CC through triples
  mrcc4 | approximate CC through quadruples
  mrcc5 | approximate CC through quintuples
  mrcc6 | approximate CC through sextuples
  mrccsdt-3 | CC through doubles with iterative triples (all but the most expensive terms)
  mrccsdtq-3 | CC through triples with iterative quadruples (all but the most expensive terms)
  mrccsdtqp-3 | CC through quadruples with iterative quintuples (all but the most expensive terms)
  mrccsdtqph-3 | CC through quintuples with iterative sextuples (all but the most expensive terms)

  Parameters:

  - name (string) –

    `'scf'` || `'df-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.

  Parameters: | bypass_scf (boolean) – `'on'` || `'off'` Indicates whether, for name values built atop of scf calculations, the scf step is skipped. Suitable when special steps are taken to get the scf to converge in an explicit preceeding scf step.
  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('mp4')

      >>> # [4] Converge scf as singlet, then run detci as triplet upon singlet reference
      >>> molecule H2 {\\n0 1\\nH\\nH 1 0.74\\n}
      >>> energy('scf')
      >>> H2.set_multiplicity(3)
      >>> energy('detci', bypass_scf=True)

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