Hello to the scholars in the forum!

As the title indicates, I failed to converge when calculating the **charge transfer integral** between more than two molecules.

I extracted a cluster from the molecular dynamics simulation results (without optimized structure after extraction), hoping to obtain the charge transfer integral between the central guest and the surrounding host. Subsequently, I calculated The intermolecular charge transfer integral according to 10.15.2.5 The frontier molecular orbital approach of *Q-Chem 5.3 User’s Manual*, but the convergence failed. How should I solve this problem?

Thank you all for your valuable suggestions.

input：

Fatal error：

50 -5713.4590711905 2.15E-02 Convergence failure

Q-Chem fatal error occurred in module scfman/scfman.C, line 5472:

SCF failed to converge

Please provide a complete input file if you want someone take a look but if DIIS error is still 2E-02 after 50 cycles, that suggests you need a better guess, possibly also a different SCF convergence algorithm.

1 Like

Thank you for your reply.

I apologize to you for my thoughtless, but I am a newcomer seems to be no permission to upload attachment, so I found a upload attachments website:

https://t.wss.pet/f/cmrsxn4oxqw

Contains input and output files.

What do you mean by different SCF convergence algorithm? Is it similar to Gaussian?

ps: I just tried to put in only three molecules, but it’s the same situation, maybe Q-Chem can’t handle more than two molecules?

Thanks again. Have a great day.

(a) can you just paste the input file here, use the </> button. I’m not comfortable downloading .rar file from a website written in a language I can’t read.

(b) see SCF_ALGORITHM in Q-Chem documentation,

https://manual.q-chem.com/latest/Ch4.S5.SS2.html

Also SCF_GUESS,

https://manual.q-chem.com/latest/sect_guess.html

1 Like

Thanks for your reply!

I am very sorry to make you feel uncomfortable, but I did this because I was afraid of having too many lines of input file for the whole cluster, and I have pasted the input file for the three molecules I used later.

The information you provided is very helpful, thank you again!

```
$molecule
0 1
--
0 1
C 14.33000000 12.35000000 15.96000000
C 14.61000000 12.88000000 14.71000000
C 13.57000000 13.30000000 13.87000000
C 12.21000000 13.12000000 14.37000000
C 11.96000000 12.58000000 15.61000000
C 13.01000000 12.18000000 16.46000000
N 10.62000000 12.37000000 16.07000000
C 10.01000000 13.46000000 16.72000000
C 6.10000000 12.86000000 18.58000000
C 10.70000000 14.71000000 16.90000000
C 9.99000000 15.75000000 17.54000000
C 8.71000000 15.55000000 18.03000000
C 8.04000000 14.32000000 17.99000000
C 8.68000000 13.25000000 17.29000000
C 8.64000000 10.85000000 16.14000000
C 5.99000000 10.59000000 18.16000000
C 4.83000000 10.44000000 18.88000000
C 4.28000000 11.59000000 19.45000000
C 4.86000000 12.75000000 19.31000000
B 7.97000000 11.89000000 17.10000000
C 6.68000000 11.76000000 17.92000000
C 9.96000000 11.06000000 15.69000000
C 10.66000000 10.05000000 14.87000000
C 10.01000000 8.94000000 14.47000000
C 8.66000000 8.77000000 14.81000000
C 8.02000000 9.69000000 15.63000000
N 6.75000000 14.10000000 18.56000000
C 6.15000000 15.19000000 19.19000000
C 6.31000000 15.41000000 20.53000000
C 5.72000000 16.54000000 21.15000000
C 4.91000000 17.40000000 20.41000000
C 4.71000000 17.13000000 19.12000000
C 5.30000000 16.06000000 18.48000000
H 15.21000000 11.96000000 16.45000000
H 15.63000000 13.04000000 14.36000000
H 13.91000000 13.73000000 12.94000000
H 11.36000000 13.45000000 13.79000000
H 12.68000000 11.81000000 17.42000000
H 11.70000000 14.94000000 16.57000000
H 10.43000000 16.73000000 17.71000000
H 8.24000000 16.35000000 18.57000000
H 6.37000000 9.64000000 17.81000000
H 4.38000000 9.47000000 19.01000000
H 3.35000000 11.39000000 19.97000000
H 4.40000000 13.61000000 19.78000000
H 11.69000000 10.22000000 14.58000000
H 10.58000000 8.21000000 13.92000000
H 8.15000000 7.92000000 14.39000000
H 6.98000000 9.47000000 15.81000000
H 6.90000000 14.84000000 21.24000000
H 5.96000000 16.72000000 22.19000000
H 4.30000000 18.20000000 20.81000000
H 4.02000000 17.78000000 18.61000000
H 5.15000000 15.90000000 17.42000000
--
0 1
C 3.11000000 6.69000000 14.83000000
C 2.30000000 5.55000000 14.58000000
C 2.82000000 4.33000000 15.01000000
C 4.09000000 4.24000000 15.66000000
C 4.89000000 5.36000000 15.91000000
C 4.32000000 6.57000000 15.48000000
C 6.26000000 5.37000000 16.62000000
C 6.55000000 6.39000000 17.58000000
C 7.78000000 6.40000000 18.26000000
C 8.72000000 5.43000000 17.94000000
C 8.47000000 4.47000000 16.99000000
C 7.26000000 4.43000000 16.38000000
N 8.04000000 7.42000000 19.26000000
N 2.70000000 7.99000000 14.46000000
C 9.14000000 8.30000000 19.26000000
C 9.02000000 9.07000000 20.43000000
C 7.86000000 8.66000000 21.12000000
C 7.26000000 7.64000000 20.40000000
C 3.50000000 8.88000000 13.68000000
C 2.82000000 10.19000000 13.57000000
C 1.61000000 10.05000000 14.26000000
C 1.55000000 8.73000000 14.81000000
C 0.64000000 10.95000000 14.53000000
C -0.46000000 10.51000000 15.32000000
C -0.51000000 9.24000000 15.89000000
C 0.51000000 8.32000000 15.59000000
C 4.77000000 8.69000000 13.05000000
C 5.27000000 9.76000000 12.44000000
C 4.64000000 10.99000000 12.30000000
C 3.45000000 11.20000000 12.86000000
C 7.30000000 9.04000000 22.29000000
C 6.19000000 8.51000000 22.82000000
C 5.57000000 7.48000000 22.15000000
C 6.10000000 7.05000000 20.88000000
C 10.16000000 8.53000000 18.31000000
C 11.04000000 9.53000000 18.61000000
C 10.95000000 10.31000000 19.80000000
C 9.93000000 10.09000000 20.68000000
H 1.32000000 5.60000000 14.13000000
H 2.19000000 3.48000000 14.78000000
H 4.34000000 3.27000000 16.07000000
H 4.79000000 7.54000000 15.64000000
H 5.90000000 7.20000000 17.91000000
H 9.62000000 5.40000000 18.54000000
H 9.19000000 3.70000000 16.72000000
H 7.02000000 3.73000000 15.58000000
H 0.58000000 11.95000000 14.11000000
H -1.28000000 11.19000000 15.49000000
H -1.36000000 8.96000000 16.49000000
H 0.55000000 7.29000000 15.92000000
H 5.33000000 7.76000000 13.07000000
H 6.20000000 9.63000000 11.91000000
H 5.20000000 11.75000000 11.77000000
H 2.93000000 12.14000000 12.73000000
H 7.97000000 9.77000000 22.74000000
H 5.92000000 8.87000000 23.80000000
H 4.73000000 6.94000000 22.56000000
H 5.62000000 6.20000000 20.40000000
H 10.31000000 7.99000000 17.38000000
H 11.85000000 9.67000000 17.90000000
H 11.66000000 11.11000000 20.02000000
H 9.81000000 10.71000000 21.56000000
--
0 1
C 1.36000000 15.33000000 15.21000000
C 0.16000000 15.03000000 14.66000000
C -0.83000000 14.43000000 15.38000000
C -0.68000000 14.09000000 16.72000000
C 0.56000000 14.39000000 17.32000000
C 1.56000000 15.05000000 16.59000000
C 0.70000000 14.02000000 18.75000000
C 1.31000000 14.90000000 19.64000000
C 1.33000000 14.58000000 21.00000000
C 0.86000000 13.41000000 21.51000000
C 0.32000000 12.55000000 20.61000000
C 0.21000000 12.80000000 19.26000000
N 1.90000000 15.51000000 21.93000000
N 2.43000000 15.91000000 14.44000000
C 2.89000000 15.27000000 22.87000000
C 3.05000000 16.42000000 23.64000000
C 2.22000000 17.46000000 23.10000000
C 1.48000000 16.87000000 22.06000000
C 3.71000000 15.37000000 14.32000000
C 4.45000000 16.18000000 13.45000000
C 3.62000000 17.23000000 13.03000000
C 2.35000000 17.05000000 13.71000000
C 3.75000000 18.29000000 12.22000000
C 2.74000000 19.24000000 12.03000000
C 1.49000000 19.04000000 12.64000000
C 1.32000000 17.92000000 13.52000000
C 4.31000000 14.18000000 14.82000000
C 5.63000000 13.87000000 14.53000000
C 6.33000000 14.75000000 13.66000000
C 5.76000000 15.89000000 13.12000000
C 2.08000000 18.81000000 23.42000000
C 1.20000000 19.57000000 22.67000000
C 0.45000000 18.99000000 21.66000000
C 0.60000000 17.66000000 21.36000000
C 3.65000000 14.10000000 23.04000000
C 4.60000000 14.06000000 24.05000000
C 4.77000000 15.18000000 24.87000000
C 4.00000000 16.34000000 24.66000000
H -0.04000000 15.15000000 13.60000000
H -1.73000000 14.16000000 14.85000000
H -1.43000000 13.65000000 17.36000000
H 2.49000000 15.28000000 17.08000000
H 1.66000000 15.84000000 19.23000000
H 0.91000000 13.21000000 22.57000000
H -0.03000000 11.60000000 21.00000000
H -0.25000000 12.14000000 18.53000000
H 4.70000000 18.34000000 11.70000000
H 2.91000000 20.08000000 11.37000000
H 0.66000000 19.72000000 12.49000000
H 0.37000000 17.75000000 14.01000000
H 3.69000000 13.58000000 15.48000000
H 6.03000000 12.97000000 14.98000000
H 7.38000000 14.52000000 13.53000000
H 6.28000000 16.57000000 12.45000000
H 2.68000000 19.18000000 24.24000000
H 1.07000000 20.64000000 22.81000000
H -0.23000000 19.52000000 21.00000000
H 0.01000000 17.29000000 20.54000000
H 3.43000000 13.28000000 22.36000000
H 5.20000000 13.17000000 24.15000000
H 5.53000000 15.00000000 25.62000000
H 4.21000000 17.20000000 25.30000000
$end
$rem
method = b3lyp
omega = 370
basis = 6-31G**
scf_print_frgm = true
sym_ignore = true
scf_guess = fragmo
sts_dc = fock
sts_trans_donor = 2-3 ! use HOMO, HOMO-1 and LUMO, LUMO+1, LUMO+2 of donor
sts_trans_acceptor = 2-3 ! use HOMO and LUMO, LUMO+1 of acceptor
$end
$rem_frgm
print_orbitals = 5
$end
```

I see that your molecule are large but they look electronically benign. I suggest setting THRESH=14. I think that the Q-Chem default value is too loose for large systems, due to linear dependency issues, my group routinely uses THRESH=12.

Update: actually, with Q-Chem 6.1 your input file runs to completion for me, with default value of THRESH. The fragment jobs take 9 SCF iterations each and then the supermolecular SCF takes 46 steps. Initial energies are very bad, though, so numerics might mean that yours takes a bit more; try increasing MAX_SCF_CYCLES.

1 Like

Thank you very much for your help, and sorry to have caused you so much trouble!

I have checked the version of qchem installed on my HPC is 5.4.2, which may be the reason for the failure to complete the calculation. I will try the two suggestions you put forward, and thank you again for your reply.

Have a nice day!

Not sure why the version should make a difference here but it did take me pretty close to the default limit of 50 cycles so small changes in numerics may put it over.