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Re^2: Problem running XMCQDPT2 calculation with large (16e,16o) active space

Alex Granovsky

Dear Martial,

I forgot to mention that you may also need to reduce the number of threads to be used in calculations.

Kind regards,
Alex Granovsky

On Thu Jan 25 '18 2:50am, Alex Granovsky wrote
>Dear Martial,
>Iíve attached the modified head of your input file to this post.

>Basically, to handle CAS(16e,16o) using current XMCQDPT2 implementation,
>you need to dramatically reduce MXBASE and to use CSFs selection.

>Note, the MQCACI (i.e. CAS CI) step is always performed using single
>CPU core and thus this step will time consuming. This is a limitation
>of present code which will be removed in the future releases.
>Kind regards,
>Alex Granovsky

>On Wed Jan 24 '18 6:53pm, Martial Boggio-Pasqua wrote
>>I have been using Firefly recently to run CASSCF and XMCQDPT2 calculations on a medium-sized organic photochromic system. This system requires a large active space: (14e,14o) to study its absorption properties and (16e,16o) to study its photoswitching mechanism. While I have been able to run XMCQDPT2 with a (14e,14o) active space, I am not able to run a similar job with a (16e,16o) active space. I cannot circumvent the memory limit in mwords. I get the following error message in MQCACI: ERROR: MEMORY REQUEST EXCEEDS MAXIMUM. 729888763 WORDS REQUIRED † †460000000 AVAILABLE.

>>Maybe someone can tell me if this calculation is possible or not. I have enclosed an input file in which the CASSCF(16,16) part is skipped as the CASSCF orbitals have been saved in a previous job.

>>I would be extremely grateful if I can get some assistance with this issue as the whole series of calculations I am planning to perform require this large (16e,16o) active space.

>>I am using the 8.2.0 version.

>>Many thanks in advance!

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