Which V-coupling value of energy transfer is correct?

Questions
#1

Hello,

I am new to Q-Chem. I found that the software can compute the V-coupling value for energy transfer, but I am not sure whether my input is correct or how to interpret the output. I would greatly appreciate any advice.

Specifically, I am interested in the V-coupling associated with energy transfer between a photosensitizer in its T₁ state and ground-state oxygen (³O₂). This corresponds to Dexter energy transfer, relevant to photodynamic therapy:

(T₁)Ps + ³O₂ → (S₀)Ps + ¹O₂.

My input file is:

$rem
   METHOD TPSSh
   BASIS def2-TZVP
   DFT_D D4
   SOLVENT_METHOD SMD
   STS_FSD TRUE
   CIS_N_ROOTS       10
   CIS_SINGLETS      true
   CIS_TRIPLETS      true
   STS_DONOR         1-30
   STS_ACCEPTOR      31-32
$end

$smx
   solvent water
$end

$comment
   EET
$end

$molecule
   0 3
   O     -2.296744   -2.636037   -0.968211
   O      0.206036   -2.461183   -0.752196
   O     -0.302321    2.762782    0.729913
   O      2.704473   -2.257589   -0.588512
   O      4.604231    1.745639    0.881824
   C     -1.334952    0.746758    0.046143
   C     -1.192059   -0.597776   -0.324505
   C      1.225901   -0.419771   -0.111092
   C      1.101576    0.926772    0.252759
   C      0.083910   -1.242222   -0.419295
   C     -0.190619    1.581981    0.368580
   C     -2.605848    1.330528    0.127365
   C     -2.366042   -1.363398   -0.616727
   C     -3.737982    0.589971   -0.162551
   C      2.546362   -1.004797   -0.220463
   C      2.234332    1.646628    0.646742
   C     -3.606182   -0.746016   -0.530377
   C      3.508965    1.077929    0.542425
   C      3.651722   -0.233973    0.078403
   C     -5.093994    1.212293   -0.087685
   H     -2.663393    2.368238    0.418378
   H      2.100911    2.654297    1.012808
   H     -4.473697   -1.347256   -0.753019
   H      4.632226   -0.675591    0.012222
   H     -5.545497    1.222949   -1.077890
   H     -5.736109    0.625488    0.565066
   H     -5.035232    2.229329    0.285655
   H     -1.342201   -2.925586   -0.977466
   H      1.806313   -2.674694   -0.744708
   H      4.394135    2.641501    1.196817
   O      2.041183    0.109198    2.744029
   O      1.519313   -0.935044    2.262480
$end

My uncertainties are as follows:

  1. I am not sure whether to use STS_FSD or STS_FED. The manual notes that FED excludes the ground state from the analysis, but I need the ground state included for ³O₂.
  2. I specified the total system as 0 3 without explicitly defining fragments (e.g., 0 1 Ps, 0 3 O₂, which also sums to 0 3). I am not confident that this setup correctly enforces the photosensitizer in T₁ and oxygen in its triplet ground state.

The relevant portion of my output is:

                    FSD ELECTRONIC-COUPLING CALCULATION


       Fragment Spins of Ground State 
 -----------------------------------------------------
   State         S(D)        S(A)          dS
 -----------------------------------------------------
       0     0.149564    1.850436   -1.700872
 -----------------------------------------------------

 Within CIS/TDA Excited States:

       Fragment Spins of Excited State 
 -----------------------------------------------------
   State         S(D)        S(A)          dS
 -----------------------------------------------------
       1     0.258255    1.741745   -1.483491 (  0.217381)
       2     0.235453    1.764547   -1.529093 (  0.171778)
       3     0.936233    1.063767   -0.127534 (  1.573338)
       4     0.258098    1.741902   -1.483804 (  0.217067)
       5     0.235280    1.764720   -1.529441 (  0.171431)
       6     0.575434    1.424566   -0.849131 (  0.851740)
       7     0.687242    1.312758   -0.625516 (  1.075355)
       8     0.962554    1.037446   -0.074891 (  1.625980)
       9     0.822590    1.177410   -0.354819 (  1.346053)
      10     0.815321    1.184679   -0.369359 (  1.331513)
 -----------------------------------------------------

               Fragment Spins of Transition Densities and
            FSD Couplings Between Ground and Excited States
 --------------------------------------------------------------------------------
    States     S12(D)     S12(A)       dS12    Coupling(eV)   FSD-dS1    FSD-dS2
 --------------------------------------------------------------------------------
    0    1  -0.018143   0.018143  -0.036285      0.2746709  -1.706768  -1.477594
    0    2  -0.006089   0.006089  -0.012177      0.1408457  -1.701731  -1.528235
    0    3   0.004742  -0.004742   0.009484    -0.01249373  -1.700929  -0.127476
    0    4  -0.001072   0.001072  -0.002144     0.02320875  -1.700893  -1.483783
    0    5   0.026552  -0.026552   0.053104     -0.6388357  -1.715989  -1.514324
    0    6   0.076665  -0.076665   0.153329     -0.4153414  -1.727633  -0.822370
    0    7  -0.058739   0.058739  -0.117478       0.265195  -1.713556  -0.612832
    0    8   0.012239  -0.012239   0.024478    -0.03862859  -1.701240  -0.074523
    0    9  -0.092387   0.092387  -0.184775      0.3443387  -1.725775  -0.329915
    0   10   0.041865  -0.041865   0.083730     -0.1654571  -1.706116  -0.364114
 --------------------------------------------------------------------------------

               Fragment Spins of Transition Densities and
            FSD Couplings Between Excited States
 --------------------------------------------------------------------------------
    States     S12(D)     S12(A)       dS12    Coupling(eV)   FSD-dS1    FSD-dS2
 --------------------------------------------------------------------------------
    1    2  -0.022584   0.022584  -0.045168     -0.1213628  -1.455695  -1.556889
    1    3   0.091768  -0.091768   0.183535    -0.04416684  -1.507894  -0.103130
    1    4  -0.027672   0.027672  -0.055344     -0.3078439  -1.428304  -1.538991
    1    5   0.033478  -0.033478   0.066956      0.3268944  -1.435677  -1.577254
    1    6   0.058255  -0.058255   0.116509     -0.1236803  -1.504212  -0.828410
    1    7  -0.053195   0.053195  -0.106390     0.09026335  -1.496486  -0.612521
    1    8  -0.009792   0.009792  -0.019585     0.01156735  -1.483763  -0.074619
    1    9   0.096739  -0.096739   0.193478     -0.1405041  -1.515736  -0.322574
    1   10   0.004786  -0.004786   0.009571   -0.007877437  -1.483573  -0.369276
    2    3   0.146756  -0.146756   0.293513    -0.01277733  -1.588078  -0.068549
    2    4   0.010671  -0.010671   0.021343     -0.1178988  -1.537566  -1.475332
    2    5  -0.001250   0.001250  -0.002499     -0.2091495  -1.526762  -1.531772
    2    6   0.011266  -0.011266   0.022532     -0.0147303  -1.529839  -0.848385
    2    7   0.089148  -0.089148   0.178297    -0.08774905  -1.563003  -0.591607
    2    8  -0.006464   0.006464  -0.012928    0.004981156  -1.529208  -0.074777
    2    9   0.135311  -0.135311   0.270622     -0.1244424  -1.588459  -0.295453
    2   10   0.015156  -0.015156   0.030313    -0.01684149  -1.529885  -0.368567
    3    4  -0.000938   0.000938  -0.001875  -0.0003839019  -0.127531  -1.483807
    3    5   0.036994  -0.036994   0.073989     0.01853574  -0.123639  -1.533335
    3    6   0.096087  -0.096087   0.192173     0.08916712  -0.079546  -0.897119
    3    7  -0.061024   0.061024  -0.122048    -0.09065213  -0.099230  -0.653820
    3    8   0.014851  -0.014851   0.029703     -0.1849485  -0.140900  -0.061526
    3    9   0.021478  -0.021478   0.042956     0.09341853  -0.119686  -0.362666
    3   10  -0.007445   0.007445  -0.014890    -0.03538849  -0.126620  -0.370272
    4    5  -0.052060   0.052060  -0.104119    -0.03688322  -1.400032  -1.613213
    4    6  -0.065880   0.065880  -0.131759     0.01950065  -1.510071  -0.822865
    4    7  -0.085399   0.085399  -0.170797     0.02482829  -1.516544  -0.592777
    4    8   0.248861  -0.248861   0.497721    -0.06249048  -1.641894   0.083198
    4    9   0.061526  -0.061526   0.123053    -0.02670689  -1.497061  -0.341563
    4   10  -0.041143   0.041143  -0.082286     0.02201707  -1.489847  -0.363316
    5    6   0.132030  -0.132030   0.264061    -0.00803021  -1.619906  -0.758666
    5    7   0.135449  -0.135449   0.270898    -0.01510652  -1.604409  -0.550548
    5    8  -0.066649   0.066649  -0.133297     0.01271638  -1.541555  -0.062777
    5    9  -0.068416   0.068416  -0.136832     0.01988441  -1.545170  -0.339090
    5   10  -0.005675   0.005675  -0.011351    0.002209949  -1.529552  -0.369248
    6    7   0.376985  -0.376985   0.753971    -0.01611253  -1.499539   0.024892
    6    8   0.097690  -0.097690   0.195380    -0.02588126  -0.895641  -0.028381
    6    9  -0.169734   0.169734  -0.339469     0.06025904  -1.021886  -0.182064
    6   10   0.001801  -0.001801   0.003601   -0.001498964  -0.849158  -0.369332
    7    8  -0.023385   0.023385  -0.046769    0.006892199  -0.629461  -0.070947
    7    9   0.175978  -0.175978   0.351956    -0.05436798  -0.867252  -0.113083
    7   10  -0.012383   0.012383  -0.024766     0.01586526  -0.627889  -0.366986
    8    9   0.008235  -0.008235   0.016471    0.001998137  -0.073926  -0.355785
    8   10   0.069647  -0.069647   0.139294     0.02915074  -0.019442  -0.424809
    9   10   0.042201  -0.042201   0.084401     0.02522624  -0.277375  -0.446803
 --------------------------------------------------------------------------------

                          END OF FSD CALCULATION

My interpretation is that State 0 corresponds to S₀ of the photosensitizer plus T₁ of O₂. However, none of the excited states seem to represent T₁ of the photosensitizer, since none of the fragment spin values approach S = 2.

How should I correctly set up the calculation so that the photosensitizer T₁ and O₂ (³O₂) are properly captured?

THANKS!

#2

I’m not an expert here, but it seems that you may need a method that requires you to specify charge and spin states explicitly for both fragments. See the “Diabatic Methods” (such as “1+1 approach”), here:
https://manual.q-chem.com/latest/topic_dc.html

#3

@jherbert , thanks. I am right now trying to run it but for the input

$rem
   METHOD TPSSh
   BASIS def2-TZVP
   DFT_D D4
   SOLVENT_METHOD SMD
   SCF_PRINT_FRGM       FALSE
   SCF_GUESS            FRAGMO
   STS_DC               TRUE
   POINT_GROUP_SYMMETRY FALSE
$end

$smx
   solvent water
$end

$comment
   EET calculation
$end

$molecule
  0 1
--
   0 3, 0 1
   O     -2.296744   -2.636037   -0.968211
   O      0.206036   -2.461183   -0.752196
   O     -0.302321    2.762782    0.729913
   O      2.704473   -2.257589   -0.588512
   O      4.604231    1.745639    0.881824
   C     -1.334952    0.746758    0.046143
   C     -1.192059   -0.597776   -0.324505
   C      1.225901   -0.419771   -0.111092
   C      1.101576    0.926772    0.252759
   C      0.083910   -1.242222   -0.419295
   C     -0.190619    1.581981    0.368580
   C     -2.605848    1.330528    0.127365
   C     -2.366042   -1.363398   -0.616727
   C     -3.737982    0.589971   -0.162551
   C      2.546362   -1.004797   -0.220463
   C      2.234332    1.646628    0.646742
   C     -3.606182   -0.746016   -0.530377
   C      3.508965    1.077929    0.542425
   C      3.651722   -0.233973    0.078403
   C     -5.093994    1.212293   -0.087685
   H     -2.663393    2.368238    0.418378
   H      2.100911    2.654297    1.012808
   H     -4.473697   -1.347256   -0.753019
   H      4.632226   -0.675591    0.012222
   H     -5.545497    1.222949   -1.077890
   H     -5.736109    0.625488    0.565066
   H     -5.035232    2.229329    0.285655
   H     -1.342201   -2.925586   -0.977466
   H      1.806313   -2.674694   -0.744708
   H      4.394135    2.641501    1.196817
--
   0 3, 0 1
   O      2.041183    0.109198    2.744029
   O      1.519313   -0.935044    2.262480
$end

Q-Chem yields error:

 Q-Chem fatal error occurred in module libgen/rem_setup.C, line 543:
 DFT is not supported for direct coupling method. Please read the manual for futher instructions
 Please submit a crash report at q-chem.com/reporter

Damn… I really need this V-coupling to conclude the paper ! :upside_down_face:

#4

I think it’s that the XC component was never implemented. Try METHOD = HF.

#5

Oh, well… HF :sweat_smile: Doesn’t sound too reliable, does it?
I’ve already done this:

$rem
METHOD HF
BASIS def2-TZVP
DFT_D D4
SOLVENT_METHOD SMD
SCF_PRINT_FRGM       FALSE
SCF_GUESS            FRAGMO
STS_DC               TRUE
POINT_GROUP_SYMMETRY FALSE
$end

$smx
solvent water
$end

$comment
EET calculation
$end

$molecule
0 1
--
0 3, 0 1
O     -2.296744   -2.636037   -0.968211
O      0.206036   -2.461183   -0.752196
O     -0.302321    2.762782    0.729913
O      2.704473   -2.257589   -0.588512
O      4.604231    1.745639    0.881824
C     -1.334952    0.746758    0.046143
C     -1.192059   -0.597776   -0.324505
C      1.225901   -0.419771   -0.111092
C      1.101576    0.926772    0.252759
C      0.083910   -1.242222   -0.419295
C     -0.190619    1.581981    0.368580
C     -2.605848    1.330528    0.127365
C     -2.366042   -1.363398   -0.616727
C     -3.737982    0.589971   -0.162551
C      2.546362   -1.004797   -0.220463
C      2.234332    1.646628    0.646742
C     -3.606182   -0.746016   -0.530377
C      3.508965    1.077929    0.542425
C      3.651722   -0.233973    0.078403
C     -5.093994    1.212293   -0.087685
H     -2.663393    2.368238    0.418378
H      2.100911    2.654297    1.012808
H     -4.473697   -1.347256   -0.753019
H      4.632226   -0.675591    0.012222
H     -5.545497    1.222949   -1.077890
H     -5.736109    0.625488    0.565066
H     -5.035232    2.229329    0.285655
H     -1.342201   -2.925586   -0.977466
H      1.806313   -2.674694   -0.744708
H      4.394135    2.641501    1.196817
--
0 3, 0 1
O      2.041183    0.109198    2.744029
O      1.519313   -0.935044    2.262480
$end

The output is:

--------------------------------------------------------------
 Start with Direct-Coupling Calculation
--------------------------------------------------------------
 There are       78 alpha and       78 beta electrons
 There are 742 basis functions and 742 orbitals
 <S^2> = 2.0800 (5554.7292)
 <S^2> = 2.0800 (2.2825)
 <S^2> = -0.1073 (-0.1196)

 Direct-Coupling Matrix Elements (a.u.):
   DC Matrix Element    Hif =    -1.0922341746
   DC Matrix Element    Sif =     0.0003744613
   DC Matrix Element    Hii = -2657.4623839184
   DC Matrix Element    Sii =     0.9112978197
   DC Matrix Element    Hff = -2615.8025813568
   DC Matrix Element    Sff =     0.8970140667

 Effective Coupling (in eV) =    -0.0077662126
--------------------------------------------------------------

But HF… I wonder how reliable it really is. By the way, do you know someone more experienced in this topic who could suggest the best approach and how to achieve it? :slightly_smiling_face:

#6

The coupling is basically just electrostatics, I think HF should be fine. All of these methods were implemented by Zhi-Qiang You and Chao-Ping Hsu, they have a review article here:
https://doi.org/10.1002/qua.24528

#7

Alright, @jherbert ! If the input is fine, then let’s take this value for granted.
But if anyone has a different opinion, I’d be more than happy to hear it.
… and I can effectively incorporate V into this equation now, I suppose?

Equation
Equation1180×344 31.9 KB

//Edit

However. One more question - why does input below fail if multiplicity of the system is set to quintet (0 5) or triplet (0 3), but works if it is singlet (0 1)?

$rem
   METHOD HF
   BASIS def2-TZVP
   DFT_D D4
   SOLVENT_METHOD SMD
   SCF_PRINT_FRGM       FALSE
   SCF_GUESS            FRAGMO
   STS_DC               TRUE
   POINT_GROUP_SYMMETRY FALSE
$end

$smx
   solvent water
$end

$comment
   EET calculation
$end

$molecule
  0 5
--
   0 3, 0 1
   O     -2.296744   -2.636037   -0.968211
   O      0.206036   -2.461183   -0.752196
   O     -0.302321    2.762782    0.729913
   O      2.704473   -2.257589   -0.588512
   O      4.604231    1.745639    0.881824
   C     -1.334952    0.746758    0.046143
   C     -1.192059   -0.597776   -0.324505
   C      1.225901   -0.419771   -0.111092
   C      1.101576    0.926772    0.252759
   C      0.083910   -1.242222   -0.419295
   C     -0.190619    1.581981    0.368580
   C     -2.605848    1.330528    0.127365
   C     -2.366042   -1.363398   -0.616727
   C     -3.737982    0.589971   -0.162551
   C      2.546362   -1.004797   -0.220463
   C      2.234332    1.646628    0.646742
   C     -3.606182   -0.746016   -0.530377
   C      3.508965    1.077929    0.542425
   C      3.651722   -0.233973    0.078403
   C     -5.093994    1.212293   -0.087685
   H     -2.663393    2.368238    0.418378
   H      2.100911    2.654297    1.012808
   H     -4.473697   -1.347256   -0.753019
   H      4.632226   -0.675591    0.012222
   H     -5.545497    1.222949   -1.077890
   H     -5.736109    0.625488    0.565066
   H     -5.035232    2.229329    0.285655
   H     -1.342201   -2.925586   -0.977466
   H      1.806313   -2.674694   -0.744708
   H      4.394135    2.641501    1.196817
--
   0 3, 0 1
   O      2.041183    0.109198    2.744029
   O      1.519313   -0.935044    2.262480
$end

with

 Q-Chem fatal error occurred in module qparser/MoleculeInput.C, line 526:

 Incorrect fragment multiplicity defined