Allocating memory in Windows


I am running Q-chem 5.3 on a windows machine. By default, it only seems to allocate 2GB RAM (MEM_TOTAL).

I was going to try and experiment with using EOM-IP-CC to calculate an XPS spectrum of a small gas-phase molecule. So I thought I good starting point would be to try and run the first example from here

When I run this, after the SCF calculation (which runs successfully), the calculation seems to crash/stop running at this point in the output file:
“Import integrals: CPU 0.00 s wall 0.00 s”

At this point Q-chem had maxed out the 2GB memory (from looking at task manager). My understanding is coupled cluster calculations are fairly memory demanding, so I thought I would try forcing Q-chem to use a bit more of the system memory using MEM_TOTAL=8000. If I then run the script, Q-chem crashes when “Allocating and initializing 7808MB of RAM”. According to windows, I had more than 8GB available

Does anyone have any ideas how to get Q-chem to allocate more than 2GB of memory on windows?


There is a known defect in Q-Chem 5.3 for Windows that prevents one from using more than 2GB memory in ADC, CC and EOM calculations. The usual symptom is a crash with the file_too_large error.

We are working on getting the issue resolved in the near future, and in the meantime the only workaround is to use Q-Chem for macOS or Linux (either through WSL on Windows or on a Linux system).

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Apologies for digging up an old thread, but I was wondering if you if this has been fixed in Q-chem 5.4? I notice in the changelog states:

2 GB limit on temporary files in CC/EOM/ADC calculations on Windows

Is this the same issue as not being able to use more than 2GB of memory?

If it has not been fixed yet, as I am upgrading to 5.4, it is perhaps worth me moving my license to a linux system.


Ah, sorry we did not follow up with a message here. Yes, this issue should now be resolved. Q-Chem 5.4 for Windows can use more than 2GB of memory for CC and ADC calculations.

No need to apologize. Thanks for confirming :smiley: