Diabatic coupling constant using fragment charge difference method

Questions
#1

Hello everyone,
I am trying to calculate diabatic coupling constants associated with the excited-state electron transfer between an organic molecule OPP and amine TEA. Initially both the OPP and TEA are neutral species. The electron transfer is happening between OPP* and TEA resulting in OPP-. and TEA.+ To calculate the diabatic coupling constant associated with this excited state electron transfer reaction I am using the generalized Mulliken-Hush/ fragment-charge difference method. I am using the following input file-
$molecule
0 1
C -0.32300000 0.10600000 0.00000000
C 1.03900000 0.10600000 0.00100000
C 1.80600000 1.31900000 0.00000000
C 1.03900000 2.53200000 -0.00100000
C -0.32300000 2.53200000 -0.00100000
C -1.09100000 1.31900000 -0.00100000
H -0.83000000 -0.85000000 0.00100000
H 1.54500000 -0.85000000 0.00100000
H 1.54600000 3.48800000 -0.00100000
H -0.83000000 3.48800000 -0.00200000
C 3.23700000 1.31900000 0.00100000
C 3.99300000 2.53100000 0.00100000
C 3.99300000 0.10700000 0.00200000
C 5.37100000 2.52200000 0.00100000
H 3.48600000 3.48600000 0.00000000
C 5.37100000 0.11600000 0.00200000
H 3.48600000 -0.84800000 0.00200000
C 6.08000000 1.31900000 0.00200000
H 5.90900000 3.46400000 0.00100000
H 5.90900000 -0.82600000 0.00300000
H 7.16400000 1.31900000 0.00300000
C -2.52200000 1.31900000 -0.00100000
C -3.27700000 2.53100000 -0.00100000
C -3.27800000 0.10700000 -0.00100000
C -4.65500000 2.52300000 -0.00200000
H -2.77000000 3.48700000 -0.00100000
C -4.65600000 0.11600000 -0.00100000
H -2.77100000 -0.84800000 0.00000000
C -5.36400000 1.32000000 -0.00200000
H -5.19200000 3.46500000 -0.00200000
H -5.19300000 -0.82600000 -0.00100000
H -6.44800000 1.32000000 -0.00200000
N -0.36701067 1.68824533 3.38249688
C -1.78167646 1.43704598 3.64136861
H -2.34179462 2.33860483 3.38114315
H -1.96051672 1.26456795 4.71923618
C -2.33498641 0.27781102 2.82151960
H -1.82964545 -0.66406760 3.04982681
H -3.40004212 0.13871039 3.02429624
H -2.20266756 0.47842941 1.75698920
C 0.49154282 0.73760452 4.08283178
H -0.01971576 -0.22725993 4.11126149
H 0.63617682 1.03764935 5.13704433
C 1.83817229 0.54474348 3.39784806
H 2.41307353 1.47358825 3.35519885
H 2.44097345 -0.19236685 3.93579612
H 1.68917631 0.19655591 2.37383897
C 0.00240226 3.06959004 3.67349322
H -0.42066889 3.39645644 4.64251497
H 1.08857714 3.11437128 3.78665143
C -0.40318539 4.03545695 2.56671014
H -1.48728570 4.06553962 2.42594594
H -0.07203163 5.04994315 2.80279685
H 0.04930877 3.72844691 1.62183403
$end
$rem
BASIS = 6-311G**
METHOD = CIS
CIS_N_ROOTS 20
CIS_SINGLETS true
CIS_TRIPLETS false
STS_GMH true !turns on the GMH calculation
STS_FCD true !turns on the FCD calculation
STS_DONOR 33-54 !define the donor fragment as atoms 1-6 for FCD calc.
STS_ACCEPTOR 1-32 !define the acceptor fragment as atoms 7-12 for FCD calc.
MEM_STATIC 4000
SOLVENT_METHOD = PCM
$end

$pcm
heavypoints 590
method swig
radii bondi
solver inversion
theory cpcm
$end

$solvent
dielectric 8.93
opticaldielectric 2.028
$end

Now the main part of the output that I obtained is-

 FCD ELECTRONIC-COUPLING CALCULATION


   Fragment Charges of Ground State with Nuclear Charges

State Q(D) Q(A) dQ

   0     0.044915   -0.044915    0.089829

Within CIS/TDA Excited States:

   Fragment Charges of Singlet Excited State with Nuclear Charges

State Q(D) Q(A) dQ

   1     0.039004   -0.039004    0.078009 ( -0.011820)
   2     0.036146   -0.036146    0.072292 ( -0.017537)
   3     0.048516   -0.048516    0.097032 (  0.007202)
   4     0.041332   -0.041332    0.082664 ( -0.007166)
   5     0.045929   -0.045929    0.091859 (  0.002029)
   6     0.047126   -0.047126    0.094252 (  0.004423)
   7     0.056071   -0.056071    0.112141 (  0.022312)
   8     0.032622   -0.032622    0.065243 ( -0.024586)
   9     0.055098   -0.055098    0.110195 (  0.020366)
  10     0.049150   -0.049150    0.098299 (  0.008470)
  11     0.833274   -0.833274    1.666547 (  1.576718)
  12     0.032797   -0.032797    0.065594 ( -0.024235)
  13     0.137694   -0.137694    0.275387 (  0.185558)
  14    -0.018564    0.018564   -0.037128 ( -0.126958)
  15    -0.014853    0.014853   -0.029706 ( -0.119535)
  16     0.037684   -0.037684    0.075368 ( -0.014462)
  17    -0.059937    0.059937   -0.119874 ( -0.209703)
  18     0.086026   -0.086026    0.172052 (  0.082223)
  19     0.025696   -0.025696    0.051392 ( -0.038437)
  20     0.063851   -0.063851    0.127702 (  0.037873)

The gist is that I are not sure how to interpret the fact that electron transfer seems to be favorable for a higher excited state than the first. For example here the 11th excited state features significant changes in the charges. So is e transfer happening at the 11th excited state? But this is of very high energy!
Do we still use the GMH/FCD coupling obtained for the 1st excited state or the charge transfer state?

Any comments and suggestion will be highly useful.

#2

Higher excited states will generally move more charge around but in general you would need to recompute diabatic states for each new set of adiabatic states, rather than recycling them.

#3

Thank you for your answer. Will you please elaborate this with an example? That will be so helpful.

#4

I’m simply saying that if you are referring to excited state #11, it seems like no surprise that would be moving considerable charge around. Furthermore, diabatic states constructed from one set of (low-lying) adiabatic states, and the electronic couplings computed using those diabatic states, are not going to be valid for higher-lying states.