Calculation of dispersion energy in Gaussian 09
The value of the empirical dispersion correction is printed when the print level is turned up using #p in the route line. For any method that contains an empirical dispersion correction, search for R6Disp or Dispersion energy, where other parts of the line will vary depending on the type of correction (-D2, -D3, or -D3(BJ)):

R6Disp:  Grimme-D2 Dispersion energy=       -0.0174233223 Hartrees.


This line is not printed with # or #n at the start of the route section.

For wavefunction methods that include dispersion via electron correlation, the dispersion contribution is non-separable. For a method like B2PLYP-D3, the printed "Dispersion energy" is the empirical correction, not the MP2 contribution!