What is the difference between actual energy vs scf energy in an orca scan

Question

Always at the end of the output of a scan type calculation in orca there are two tables one with the name "The Surface Calculated using the 'Actual Energy'" and the other "The Surface Calculated using the SCF energy". Does anyone know the difference between them? It usually has the same relative energy.

output exemple:

**** RELAXED SURFACE SCAN DONE ***

                    SUMMARY OF THE CALCULATED SURFACE

----------------------------
RELAXED SURFACE SCAN RESULTS
----------------------------

Column   1: NONAME

The Calculated Surface using the 'Actual Energy'
   1.50000000 -3201.57173598
   1.55102041 -3201.57066102
   1.60204082 -3201.56781233
   1.65306122 -3201.56367690
   1.70408163 -3201.55862728
   1.75510204 -3201.55294821
   1.80612245 -3201.54686651
   1.85714286 -3201.54056344
   1.90816327 -3201.53418950

The Calculated Surface using the SCF energy
   1.50000000 -3201.54720589
   1.55102041 -3201.54612301
   1.60204082 -3201.54326595
   1.65306122 -3201.53912278
   1.70408163 -3201.53406164
   1.75510204 -3201.52836994
   1.80612245 -3201.52227300
   1.85714286 -3201.51595184
   1.90816327 -3201.50954958

Answer 1

The "actual energy" is your final energy at that particular geometry. For HF method both SCF and Actual Energies will be same (also true for many DFT functionals).

But in the case of higher level theories, which include correction on top of SCF energy, for example:- electron correlation energy correction etc.,

actual energy  =  'SCF energy' + 'correction energy'.

This is true for all other methods including DFT (especially double hybrids, where three files will be generated, "SCF energy", "Actual Energy" and "MP2 energy").

As a rule of thumb, always go with "Actual Energy" to extract your final single-point energy at that particular point.

Answer 2

The 'Actual Energy' is the final single point energy, and in contrast to the SCF energy it contains things like the dispersion correction.