where E_{elect} is the electronic energy, E_{nuc} is the nuclear-nuclear repulsion energy, -E_{isol}
is the energy required to strip all the valence electrons off all the atoms in
the system, E_{atom} is the total heat of atomization of all the atoms in the system,
and E_{bits} is the energy from hydrogen bonds and dispersion.
These energies can be printed by adding keyword DISP.

Solvation effects

If EPS=n.nn is also present, then solvation
effects are modeled. The energy due to the stabilization of the system as
a result of the solvent is printed on the line "DIELECTRIC ENERGY". The
destabilization of the solvent due to the system is not printed. Energies
due to solvation are present in the terms E_{elect}
and E_{nuc}, that is, the solvation terms are included in these
two quantities, and cannot be separated from them. Thus, the E_{elect}
and E_{enuc} terms for a solvated system, E_{elect}(solvated)
and E_{enuc}(solvated) should be thought of as:

E_{enuc}(solvated) = E_{enuc}
+ (some other solvation terms)

The easiest way to calculate the solvation energy would be to calculate the
solvated system, then, in a separate job and using the final geometry from the
solvated calculation, do a 1SCF calculation but without solvation, then take the
difference in heats of formation.

An alternative would be to calculate the heat of formation using solvent, and
in a separate job, run the same calculation but without solvent. The
solvent effect would then be obtained by taking the difference in the two heats
of formation.

Because the "TOTAL ENERGY" includes E_{elect}
and E_{nuc}, that term also includes the solvation effects.

Single atom

For a single atom, there is no nuclear term, therefore:

ΔH_{f} = E_{elect}
- E_{isol} + E_{atom}

But E_{elect} = E_{isol} for an isolated atom,
therefore

ΔH_{f} = E_{atom}

where E_{atom} is the experimental heat of formation of the
isolated atom from the element in its standard state. For example, in nitrogen
this is half the heat required to break a N_{2} molecule into its
separated atoms. Isolated nitrogen atoms have the configuration 1s^{2}
2s^{2} 2p^{3}, and the state 4S_{u},
i.e. quartet S. Experimentally, this energy is 113 kcal/mol. This means
that all semiempirical methods predict the heats of formation of isolated atoms
with a zero error, except in those few instances when the predicted ground state
is incorrect.