[Columbus] CASCI extraordinary memory demand

[Aleksandr Zaichenko]

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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