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mcurie747

Member

Registered: 2019-12-12

Posts: 21

[SOLVED] BLB element RASSCF calculation

Hello everyone!
I just wanna know what does "max BLB element" mean in a RASSCF calculation.
Thank you

jxzou

Member

Registered: 2020-09-11

Posts: 14

Re: [SOLVED] BLB element RASSCF calculation

I'm not a molcas developer, but happened to read several super-CI papers recently. As far as I know, 'BLB' is for "Brillouin-Levy-Berthier", three pioneers of the generalized Brillouin theorem (GBT). The related papers are
[1] Generalized Brillouin Theorem for Multiconfigurational SCF Theories, Int. J. Quantum Chem., VOL. II, 307-319, 1968.
[2] Multiconfiguration wavefunctions obtained by application of the generalized Brillouin theorem. 12:44-48, 1971.
[3] A complete active space SCF method (CASSCF) using a density matrix formulated super-CI approach. Chem. Phys., 48:157–173, 1980.
[4] The complete active space SCF method in a Fock-matrixbased super-CI formulation. Int. J. Quantum Chem., 18-S14:175–189, 1980.

The super-CI method for optimizing MCSCF orbitals is based on the "generalized Brillouin theorem" (GBT), which iteratively minimize the BLB matrix elements (3 types in fact)
<0|HE_{ai}|0>, doubly occ -> vir
<0|HE_{ti}|0>, doubly occ -> active orbital
<0|HE_{at}|0>, active orbital -> vir
where E_{xx}|0> is actually a spin-adapted singlet excited configuration.

Upon convergence, all BLB matrix elements should be zero.

Last edited by jxzou (2020-09-15 04:10:34)

mcurie747

Member

Registered: 2019-12-12

Posts: 21

Re: [SOLVED] BLB element RASSCF calculation

Thank you jxzou! Problem solved.