The energy of stabilization of a donor-acceptor interaction is given as the E(2) value in this NBO report:
SECOND ORDER PERTURBATION THEORY ANALYSIS OF FOCK MATRIX IN NBO BASIS
Threshold for printing: 0.01 kcal/mol
E(2) E(j)-E(i) F(i,j)
Donor NBO (i) Acceptor NBO (j) kcal/mol a.u. a.u.
within unit 1
1. BD ( 1) C 1- C 2 204. RY*( 1) O 3 1.86 1.86 0.053
1. BD ( 1) C 1- C 2 1308. BD*( 1) N 7- C 8 5.31 1.46 0.079
152. LP ( 1) O20 1237. BD*( 1) N69- H74 8.25 1.68 0.105
140. CR ( 1) C80 1110. RY*( 3) C83 1.32 13.77 0.120
It would be really nice if the E(2) value could be depicted graphically. A point in a color spectrum corresponding to the value could appear in the overlap of the donor PNBO and the acceptor PNBO. PNBOs are better for showing overlap than the NBOs. Donor acceptor interactions are directional, so a particular interaction is specified by an ordered pair of NBO IDs, but there is no conflict with an interaction in the reverse direction since in how these things work there won't be one. If the mouse pointer was placed on one of the overlaps, the numeric E(2) value associated with the color would be shown. The ability to show the overlaps from a particular donor to all its acceptors and show overlaps to a particular acceptor from all its donors is highly desirable. A threshold of E(2) value would further subset which overlaps were shown.
Also, it is desirable that the pairwise steric exchange energies (another NBO report) receive a similar treatment. Both directions exist in this case, but the value should be the same in both cases so the same approach (showing a color in the PNBO overlap) would work.
As it stands these values have to be looked up from a long text report and a graphical depiction would be so much more convenient.
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