Hello, I am going through the tutorial for ADAPT-VQE again to make sure I didn’t miss anything, but when I ran the codes I got completely different results. The link to there tutorial is here.

The first issue I encountered is that some of the gradient is 0 for some reason when it really shouldn’t be. What I got:

```
Excitation : [0, 1, 2, 3], Gradient: 0.0
Excitation : [0, 1, 2, 5], Gradient: 0.0
Excitation : [0, 1, 2, 7], Gradient: 0.0
Excitation : [0, 1, 2, 9], Gradient: 0.034264511701721276
Excitation : [0, 1, 3, 4], Gradient: 0.0
Excitation : [0, 1, 3, 6], Gradient: 0.0
Excitation : [0, 1, 3, 8], Gradient: -0.008566127925430305
Excitation : [0, 1, 4, 5], Gradient: 0.0
Excitation : [0, 1, 4, 7], Gradient: 0.0
Excitation : [0, 1, 4, 9], Gradient: 0.0
Excitation : [0, 1, 5, 6], Gradient: 0.0
Excitation : [0, 1, 5, 8], Gradient: 0.0
Excitation : [0, 1, 6, 7], Gradient: 0.0
Excitation : [0, 1, 6, 9], Gradient: 0.0
Excitation : [0, 1, 7, 8], Gradient: 0.0
Excitation : [0, 1, 8, 9], Gradient: 0.0
```

What is Expected:

```
Excitation : [0, 1, 2, 3], Gradient: -0.01278217515766102
Excitation : [0, 1, 2, 5], Gradient: 1.5585406229479133e-19
Excitation : [0, 1, 2, 7], Gradient: 3.6591823321385755e-19
Excitation : [0, 1, 2, 9], Gradient: 0.03426451170167856
Excitation : [0, 1, 3, 4], Gradient: 1.6940658945086012e-19
Excitation : [0, 1, 3, 6], Gradient: -1.3552527156068781e-20
Excitation : [0, 1, 3, 8], Gradient: -0.03426451170167851
Excitation : [0, 1, 4, 5], Gradient: -0.023581529020676145
Excitation : [0, 1, 4, 7], Gradient: 0.0
Excitation : [0, 1, 4, 9], Gradient: 0.0
Excitation : [0, 1, 5, 6], Gradient: 0.0
Excitation : [0, 1, 5, 8], Gradient: 1.151964808265851e-19
Excitation : [0, 1, 6, 7], Gradient: -0.023581529020676173
Excitation : [0, 1, 6, 9], Gradient: 0.0
Excitation : [0, 1, 7, 8], Gradient: -1.35525271560683e-20
Excitation : [0, 1, 8, 9], Gradient: -0.12362273485599037
```

Note: It is exactly the same code that I had copy and pasted, so I don’t think the code is the issue here.

After that I’ve encountered another issue that is probably tie to the first and it is the fact that the algorithm does not converge properly.

What I got:

```
n = 0, E = -7.85513767 H, t = 1.17 s
n = 1, E = -7.85585993 H, t = 1.21 s
n = 2, E = -7.85642249 H, t = 1.20 s
n = 3, E = -7.85686535 H, t = 1.21 s
n = 4, E = -7.85721832 H, t = 1.22 s
n = 5, E = -7.85750361 H, t = 1.21 s
n = 6, E = -7.85773773 H, t = 1.21 s
n = 7, E = -7.85793296 H, t = 1.23 s
n = 8, E = -7.85809846 H, t = 1.23 s
n = 9, E = -7.85824102 H, t = 1.15 s
n = 10, E = -7.85836572 H, t = 1.24 s
n = 11, E = -7.85847636 H, t = 1.23 s
n = 12, E = -7.85857579 H, t = 1.21 s
n = 13, E = -7.85866614 H, t = 1.21 s
n = 14, E = -7.85874902 H, t = 1.24 s
n = 15, E = -7.85882566 H, t = 1.23 s
n = 16, E = -7.85889701 H, t = 1.14 s
n = 17, E = -7.85896378 H, t = 1.21 s
n = 18, E = -7.85902654 H, t = 1.25 s
n = 19, E = -7.85908573 H, t = 1.26 s
```

Note: If you graph this using any software, you will see that this does not converge in 20 iterations. However, it will converge after around 100+ iterations which is unexpected because the result from the tutorial converged at around 15-20+ iterations. Also, I realized that the algorithm is always around 1-1.3 seconds while the same algorithm on the tutorial is around 2-2.5 seconds.

What is Expected:

```
n = 0, E = -7.86266587 H, t = 2.66 s
n = 1, E = -7.87094621 H, t = 2.71 s
n = 2, E = -7.87563100 H, t = 2.21 s
n = 3, E = -7.87829146 H, t = 2.65 s
n = 4, E = -7.87981705 H, t = 2.19 s
n = 5, E = -7.88070477 H, t = 2.62 s
n = 6, E = -7.88123143 H, t = 2.16 s
n = 7, E = -7.88155161 H, t = 2.61 s
n = 8, E = -7.88175217 H, t = 2.21 s
n = 9, E = -7.88188237 H, t = 2.77 s
n = 10, E = -7.88197041 H, t = 2.20 s
n = 11, E = -7.88203267 H, t = 2.64 s
n = 12, E = -7.88207879 H, t = 2.68 s
n = 13, E = -7.88211452 H, t = 2.19 s
n = 14, E = -7.88214335 H, t = 2.76 s
n = 15, E = -7.88216743 H, t = 2.33 s
n = 16, E = -7.88218814 H, t = 2.68 s
n = 17, E = -7.88220634 H, t = 2.17 s
n = 18, E = -7.88222261 H, t = 2.62 s
n = 19, E = -7.88223734 H, t = 2.17 s
```