Excitation energy transfer between two carotinoids

Questions
#1

Dear all, I try to calculate EET between two carotinoids, the input I use is

$rem
   JOBTYPE               SP
   METHOD                CAM-B3LYP
   BASIS                 cc-pvdz
   STS_DC                TRANS
   SCF_GUESS             FRAGMO
   SYM_IGNORE            TRUE
   SCF_PRINT_FRGM        TRUE
   STS_DC_BSSE           0
   STS_TRANS_DONOR       1-3
   STS_TRANS_ACCEPTOR    1-3
   CIS_N_ROOTS           6
   RPA                   true
   CIS_SINGLETS          TRUE
   CIS_TRIPLETS          FALSE

$end

As a result I get the following output

                                              Dipole-Dipole
              Coulomb (eV)    Exchange (eV)  Interaction (eV)
           ---------------  ---------------  ---------------
 ( 1, 1):     0.0821364763  -5.92857161E-05      0.163275372
 ( 1, 2):   0.000849430442  -1.19920821E-05    -0.0335324991
 ( 1, 3):    -0.0282492014   2.96991299E-05     -0.011503185
 ( 2, 1):     -0.033654202   7.87564419E-05    -0.0203956518
 ( 2, 2):    -0.0134022876   2.00656371E-05    0.00905941245
 ( 2, 3):     0.0273009376  -4.73924655E-05   0.000723470518
 ( 3, 1):     0.0213574712   2.01927833E-06     0.0472192075
 ( 3, 2):   -0.00345989093   2.14313877E-06    -0.0100915624
 ( 3, 3):   -0.00374718561  -4.29683266E-06   -0.00335846409
--------------------------------------------------------------
My questions are (1) what does the negative cuplings mean? (2) Am I using right keywords?

Thank you!
#2

I’m not sure, but typically only the magnitude of the coupling affects the rate (e.g., in Fermi’s Golden Rule it’s the square of the coupling that appears); sign tells you about orientation. See this paper from Q-Chem’s EET group,
https://doi.org/10.1063/1.3467882
where in Fig. 9 it’s the absolute value of the coupling that the authors plot.

1 Like
#3

Thanks a lot! However it is a bit suspicious to me that the sign was not discussed at all. If there is any chance to refer to the sign discussion I would really appriciate that. Thanks again!

#4

All of that code comes from Chao-Ping Hsu’s group at Academia Sinica; see, e.g., this review article: DOI 10.1002/qua.24528
You could try contacting the PI directly.