Gaussian 16 Frequently Asked Questions

Gaussian FAQs

How can I get a breakdown of the SCF or DFT energy into all its component parts?

The full breakdown of the energy is not part of the normal output, but you can get it with two changes change to your input. First, add ExtraLinks=L608 to the route section for your calculation. Next, add input after the geometry specification to tell Link 608 what kind of calculation you are doing. The information you need is in the online G16 IOPs Reference, under the listing for IOp(3/74).

In this example, the added information is highlighted with a different color.

#P b3lyp/6-31g* ExtraLinks=L608
Gaussian Test Job 135: Fe=O perpendicular to ethene, in triplet state.

0 3
Fe X  RXFe
C1 X  RXC  Fe  90.
C2 X  RXC  Fe  90.  C1  180.
O  X  RXO  C1  90.  Fe    0.
H1 C1 RCH  C2 CCH   Fe  Angle1
H2 C1 RCH  C2 CCH   Fe -Angle1
H3 C2 RCH  C1 CCH   Fe  Angle2
H4 C2 RCH  C1 CCH   Fe -Angle2

RXFe  1.7118
RXC   0.7560
RXO   3.1306
RCH   1.1000
Angle1 110.54
Angle2 110.53
CCH   117.81

The value -5 is used in this case because this is a B3LYP calculation, and the IOp(3/74)
value corresponding to B3LYP is -5. The appropriate value for this parameter for other methods can be found in the IOps Reference or from the ouput of a previous DFT calculation run with #P on the route card, as highlighted in the partial output below:

 #P B3LYP/6-31g* ...

For Hartree-Fock energies, the value is 100, but this will not be printed in the
output because it is a default value.

What does the output from Link 608 mean?

In the output below, which is from the preceding input file, we’ve highlighted
the important parts of the output. An explanation of each term is given after the example output.

 Symmetry not used in FoFCou.
 ET = 1414.828655 EV = -3843.476430  EJ = 849.492336 EK = -74.206791 ENuc = 238.494946
A=0 I= 1 IExCor= 402 IRadAn= 4 ScaHFX= 0.200000 ScaDFX= 0.800000 0.720000 1.000000 0.810000 HFx= 0.000000 0.000000 1.000000 0.000000 0.000000 DFx= 0.000000 0.000000 1.000000 0.000000 0.000000 DFc= 0.000000 0.000000 1.000000 0.000000 0.000000 ENTVJ = -1340.660494 Ex = -74.112334 Ec = -2.536856 ETotM2e = -2251.9606613255 ETot = -1417.3096838703

These are the various components of the energy:

  • ET: Kinetic energy
  • EV: Electron-Nucleus Attraction
  • EJ: Coulomb term
  • EK: Hartree-Fock Exchange using the DFT density
  • ENuc: Nucleus-Nucleus Repulsion
  • ScaHFX: Scaling factor for the HF exchange
  • ScaDFX: Scaling factor for the DFT exchange
  • ENTVJ:ENuc + ET + EV + EJ
  • Ex: Exchange term = EK * ScaHFX + DFT-Exchange * ScaDFX
  • Ec: Correlation term
  • ETot: Total Energy (SCF Energy) = ET + EV + EJ + Ex + Ec + ENuc

Note that the value of the DFT-Exchange can be obtained using EK, ScaHFX and ScaDFX and the Ex equation shown above.

Last updated on: 14 August 2016.