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Re^3: Problem running XMCQDPT2 calculation with large (16e,16o) active space

Martial Boggio-Pasqua

Dear Alex,

many thanks for your answer and solution to my problem. I have run the job with your modified input file and it works. I suppose that I have to check the convergence of the transition energies I get depending on the value of the THRWGT variable which reduces the number of CSFs used in the XMCQDPT2 calculation. What is the meaning of the 2000000 number after iselct(1)=-4? Is it the maximum allowed number of CSFs to be selected?

On Thu Jan 25 '18 2:59am, Alex Granovsky wrote
>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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