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LASSCF localize_init_guess can't always preserve an ROHF wave function. #45

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MatthewRHermes opened this issue Nov 6, 2023 · 1 comment
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convergence issues The code has no trouble identifying the right answer, but has trouble getting to it enhancement New feature or request

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@MatthewRHermes
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If the number of active orbitals equals the number of singly-occupied orbitals of a ROHF reference wave function, then with the kwarg freeze_cas_spaces=True the localize_init_guess function will ensure that the ROHF reference wave function exists within the initial guess orbital Hilbert space. However, if doubly-occupied or unoccupied orbitals are included in the active space, then the localization will deoptimize them even if freeze_cas_spaces=True and even if such orbitals are already highly localized (because they will always have at least some tail on atoms outside the fragment).

@MatthewRHermes
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This is not a new issue; rather it is a clarification of the underlying reason why certain seemingly-simple LASSCF orbital optimizations have historically been very difficult.

@MatthewRHermes MatthewRHermes added enhancement New feature or request convergence issues The code has no trouble identifying the right answer, but has trouble getting to it labels Nov 8, 2023
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convergence issues The code has no trouble identifying the right answer, but has trouble getting to it enhancement New feature or request
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