[Columbus] CASCI extraordinary memory demand

[Hans Lischka]

Hi Aleksandr,
I am not sure what kind of calculation you really did. The CI module is 
meant to do a MR-CISD calculation. I assume you took the CAS(6,20) as 
reference? How did you proceed further? The CI program will want to 
create all SD excitation from the 38760 configurations. Did you opt for 
that? This would explaining the 1TB of memory required. Look into the 
cidrtls file. There you will see the CI dimension. If you want the CASCI 
calculation you should input zero excitations (into the virtual space).
Please let e know what you did.
Best regards, Hans

On 3/24/2025 2:36 PM, Aleksandr Zaichenko via Columbus wrote:
> Dear Columbus Team, I have a question about an ressources requirement 
> issue with the CI module for the CASCI calculation. A calculation with 
> active space CAS(6,20) without any external excitations (all lower 
> orbitals are frozen, all higher orbitals
> Dear Columbus Team,
>
> I have a question about an ressources requirement issue with the CI 
> module for the CASCI calculation. A calculation with active space 
> CAS(6,20) without any external excitations (all lower orbitals are 
> frozen, all higher orbitals are removed) contains 38760 CI-vectors (as 
> should be) and I should get an CI-only solution for only one first 
> root. Most QC programs do this calculation without any problem, but 
> the Columbus CI module requires more than 1 Tb memory for that and it 
> seems very demanding. Why is it so? Do I understand correctly, that 
> the program tries to construct a full-CI problem for all of the 38760 
> roots despite 1 root being required?
>
> Best,
> Aleksandr
>
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