Too many atoms of one type in orbmat

Questions
#1

Hello,

I am performing ground-state calculations on explicitly solvated molecules. For some systems (e.g., ethylene with 500 water molecules and phenanthrene with 100 cyclohexane molecules), I encounter the error message: “too many atoms of one type in orbmat.”
Although these systems are fairly large, their sizes still seem quite reasonable to me. Has anyone else encountered this error and found a way to resolve it?

Thank you in advance for your help.
Robin Crits

#2

we will need an input file to diagnose this. And if you can include the exact end of the output file, that may be helpful also.

#3

Please find my two input files called “ethylene_water_qchem.inp” and “phenanthrene_cyclohexane_qchem.inp” on my github page.

The last lines of my outputs are the following:
`
RESTRICTED (RHF) MOLECULAR ORBITAL COEFFICIENTS

Q-Chem fatal error occurred in module 0, line 176:

too many atoms of one type in orbmat

`

#4

I’m running this to be sure but I think you’ve hit some kind of hard-coded maximum on the number of MOs that can be printed. Do you actually want the MOs? Not sure what you are hoping to learn; they will be delocalized everywhere over all the solvent molecules. If you just want the SCF energy, you could use SKIP_ANLMAN = TRUE in $rem to bypass the wave function analysis routines.

#5

Thanks for your answer. Yes I want the MOs. I need them to compute properties with another software.

#6

It looks like there’s a hard-coded maximum of 1,000 atoms for printing. You would need to contact Q-Chem support to request that this be extended, unless you have source code access in which case please post a question on the developer forum and I can indicate what needs to be changed.

#7

Does the error occur when using SKIP_ANLMAN = TRUE but generating a fchk file? Can you use a fchk file for your analysis?

#8

I have a fix and will check it into the trunk soon.

#9

Thank you very much Prof. Herbert. My supervisor will have a look at it.

#10

I have removed this hard-coded limitation in the current version of Q-Chem trunk. If you have source code access, then a simple update should fix your problem now. The fix will ship with Q-Chem v. 6.4 in December 2025. If you do not have source code access and can’t wait until December, you would need to contact Q-Chem technical support and see if they are willing to provide an updated binary.