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

Alex Granovsky

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!

This message contains the 2 kb attachment
[ zzz.inp ]

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