Dear All,

I am new to NTO theory but I want to use it to interpret the excited state of some radical using TD-DFT in Q-Chem.
Using OH radical as an example, at TD-B3LYP/6-31+G*, and I obtain these data

Now I have following questions:

1) For the first excited state, with TDA, there is a transition between D(4)-->S(1),
******************************************
Excited state 1: 0.2868 eV
Norm of X vector = 1.000e+00
D( 4) --> S( 1) ampl = 0.9963 beta (99.3 %)
These amplitudes account for 99.3 % of the total norm
******************************************
I am not familiar with the notation used in Q-Chem, does it means electron from the 4th doubly occupied orbitals to the first singly occupied orbitals? I think Gaussian label the orbitals in excitation in a different but I cannot check it at the moment.

2) When I try to understand what orbitals involves in this excitation by NTOs
*****************************************
Excited state 1: 0.2868 eV
e-/hole pair 1 beta : ampl = 0.9995 (99.9 %)
These amplitudes account for 99.9 % of total norm
*****************************************
I though it is a single pair of particle/hole, but I still got 2 paris from Q-Chem (Yes, I set NTO_Pairs=2) What does the second pair NTOs means here? Can I generate a single orbital plot to represent this excitation?

(MOLDEN data for the first excited state is given at the bottom of this message.)
*********************************************************************************
=======================================================
TDA excitation amplitudes in the canonical MO basis
(Print if |ampl| > 0.15)
=======================================================
Excited state 1: 0.2868 eV
Norm of X vector = 1.000e+00
D( 4) --> S( 1) ampl = 0.9963 beta (99.3 %)
These amplitudes account for 99.3 % of the total norm

Excited state 2: 4.3526 eV
Norm of X vector = 1.000e+00
D( 3) --> S( 1) ampl = 0.9962 beta (99.2 %)
These amplitudes account for 99.2 % of the total norm

...
======================================================
TDA excitation amplitudes in the NTO basis
(Print if |ampl| > 0.15)
======================================================
Excited state 1: 0.2868 eV
e-/hole pair 1 beta : ampl = 0.9995 (99.9 %)
These amplitudes account for 99.9 % of total norm

Excited state 2: 4.3526 eV
e-/hole pair 1 beta : ampl = 0.9987 (99.7 %)
These amplitudes account for 99.7 % of total norm
*********************************************************************************
[Molden Format]
[Atoms] (Angs)
H 1 1 0.00000000 0.00000000 -0.87389422
O 2 8 0.00000000 0.00000000 0.10923678
[GTO]
1 0
S 3 1.000000
1.87311370E+01 3.34946000E-02
2.82539370E+00 2.34726950E-01
6.40121700E-01 8.13757330E-01
S 1 1.000000
1.61277800E-01 1.00000000E+00

2 0
S 6 1.000000
5.48467170E+03 1.83110000E-03
8.25234950E+02 1.39501000E-02
1.88046960E+02 6.84451000E-02
5.29645000E+01 2.32714300E-01
1.68975700E+01 4.70193000E-01
5.79963530E+00 3.58520900E-01
SP 3 1.000000
1.55396160E+01 -1.10777500E-01 7.08743000E-02
3.59993360E+00 -1.48026300E-01 3.39752800E-01
1.01376180E+00 1.13076700E+00 7.27158600E-01
SP 1 1.000000
2.70005800E-01 1.00000000E+00 1.00000000E+00
SP 1 1.000000
8.45000000E-02 1.00000000E+00 1.00000000E+00
D 1 1.000000
8.00000000E-01 1.00000000E+00

[MO]
Sym=X
Ene= -0.019247
Spin=Alpha
Occup=1
1 2.244595171094e-09
2 1.202347233368e-09
3 6.562121439348e-09
4 -1.620994898729e-08
5 2.518654115467e-07
6 6.719093092119e-01
7 -3.281702598545e-09
8 -1.823339593796e-08
9 1.365268673679e-07
10 4.209455160428e-01
11 -1.954638758763e-09
12 3.324324178016e-09
13 -6.793544563555e-09
14 9.779277904069e-02
15 -7.976587650132e-10
16 1.176058144770e-09
17 1.352689272967e-09
18 9.235117075482e-10
19 4.251838662625e-10
20 -9.821464872631e-09
21 -2.838681769312e-02
Sym=X
Ene= -0.019319
Spin=Alpha
Occup=1
1 1.079167702455e-09
2 -5.024022479239e-09
3 -4.289082524842e-09
4 1.125151722107e-08
5 6.944336253452e-01
6 -2.083239287177e-07
7 3.445857140226e-09
8 1.011674587817e-08
9 4.162329647193e-01
10 -1.454626920332e-07
11 1.829529489828e-09
12 1.963486087112e-09
13 6.293459121506e-02
14 -6.089492926032e-08
15 -1.375514919526e-09
16 5.227934965527e-10
17 -1.666172033121e-10
18 1.942015710429e-10
19 -3.208510256496e-10
20 -2.856826488708e-02
21 9.373779728247e-09
Sym=X
Ene= 0.019319
Spin=Alpha
Occup=0
1 -3.779557867488e-01
2 3.181555256432e-01
3 -6.420177008741e-02
4 -1.599297015087e+00
5 -1.612566301645e-02
6 -1.985265154057e-01
7 -2.371218346794e-01
8 3.475911598180e+00
9 2.484884521578e-02
10 2.936271933316e-01
11 1.456372127384e-01
12 -1.379781955229e+00
13 -1.229014935884e-02
14 -1.260293537149e-01
15 -9.371607225185e-03
16 -3.702755873978e-01
17 -3.906978370906e-01
18 -5.972162302749e-01
19 1.842039161081e-02
20 -1.143197630743e-02
21 3.911146800412e-02
Sym=X
Ene= 0.019247
Spin=Alpha
Occup=0
1 2.035702877290e-01
2 -1.840173686214e-01
3 -2.796631998238e-03
4 1.532564674065e-02
5 -3.882805214410e-03
6 8.982475125602e-02
7 -1.768101983446e-01
8 7.728027613594e-03
9 6.091152783879e-03
10 -1.391432493865e-01
11 3.845356972625e-01
12 8.678999622647e-02
13 -3.006400816142e-03
14 7.059142143275e-02
15 -2.246628687154e-01
16 -5.768567885549e-02
17 -4.918252569358e-02
18 3.295116085677e-02
19 -2.540152668836e-02
20 -4.611616771579e-04
21 3.544734275966e-02
Sym=X
Ene= -0.006122
Spin=Beta
Occup=1
1 2.244595171094e-09
2 1.202347233368e-09
3 6.562121439348e-09
4 -1.620994898729e-08
5 2.518654115467e-07
6 6.719093092119e-01
7 -3.281702598545e-09
8 -1.823339593796e-08
9 1.365268673679e-07
10 4.209455160428e-01
11 -1.954638758763e-09
12 3.324324178016e-09
13 -6.793544563555e-09
14 9.779277904069e-02
15 -7.976587650132e-10
16 1.176058144770e-09
17 1.352689272967e-09
18 9.235117075482e-10
19 4.251838662625e-10
20 -9.821464872631e-09
21 -2.838681769312e-02
Sym=X
Ene= -0.999484
Spin=Beta
Occup=1
1 1.079167702455e-09
2 -5.024022479239e-09
3 -4.289082524842e-09
4 1.125151722107e-08
5 6.944336253452e-01
6 -2.083239287177e-07
7 3.445857140226e-09
8 1.011674587817e-08
9 4.162329647193e-01
10 -1.454626920332e-07
11 1.829529489828e-09
12 1.963486087112e-09
13 6.293459121506e-02
14 -6.089492926032e-08
15 -1.375514919526e-09
16 5.227934965527e-10
17 -1.666172033121e-10
18 1.942015710429e-10
19 -3.208510256496e-10
20 -2.856826488708e-02
21 9.373779728247e-09
Sym=X
Ene= 0.999484
Spin=Beta
Occup=0
1 -2.116838215575e-09
2 2.553633911471e-09
3 -4.769054544799e-10
4 3.539563062505e-10
5 6.488467511963e-01
6 5.142737435866e-07
7 2.711103923597e-09
8 2.037825915358e-09
9 4.306917912862e-01
10 3.410922558187e-07
11 1.516047523885e-09
12 -4.370071649897e-10
13 1.225028550221e-01
14 9.772644108737e-08
15 1.284706044602e-09
16 5.785829039508e-11
17 -9.381884666867e-11
18 -6.435762335206e-10
19 3.775936035061e-10
20 -2.719270859545e-02
21 -2.148288587346e-08
Sym=X
Ene= 0.006122
Spin=Beta
Occup=0
1 3.505168316967e-09
2 -1.391471640385e-08
3 1.701914145107e-09
4 2.851199123191e-09
5 1.187291049405e-08
6 -3.180304416200e-09
7 6.369280251685e-10
8 -2.155135643719e-08
9 -5.215889484509e-09
10 7.102145108023e-10
11 2.753248063905e-10
12 2.205289792692e-08
13 -1.248581267011e-08
14 4.863518992852e-09
15 -7.516390174771e-09
16 -1.372365093130e-06
17 1.380595832358e-06
18 6.281795588483e-09
19 9.999999999987e-01
20 8.207732712260e-10
21 3.370298423960e-09
*********************************************************************************

Thanks a lot

Chiensh