Allocating memory in Windows

[Rob]

Hi

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

Simulating core photoelectron spectroscopy using the equation-of-motion coupled-cluster method for ionization potentials with the frozen-core and core-valence-separation approximations ((fc)-CVS-EOM-IP-CC)

X-ray lasers can trigger core ionization in a molecular system. The leaving electrons feel the electronic interaction in the molecular environment and thus carry the information of the electronic structure. Thanks to energy separation and locality of core ionizations, core photoelectron spectroscopy with X-ray has excellent element selectivity and spatial resolution, which makes it a powerful experimental tool in modern chemistry, physics, materials science and biology. As correlation plays an …

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?

Cheers!

[epif]

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).

[Rob]

Hi

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.

Thanks

[epif]

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.

[Rob]

No need to apologize. Thanks for confirming