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GASCompres.pdf (1006.13 kB)
Compression of Spin-Adapted Multi-Configurational Wave Functions in Exchange-Coupled Polynuclear Spin Systems
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submitted on 09.10.2019 and posted on 16.10.2019by Giovanni Li Manni, Werner Dobrautz, Ali Alavi
We present a protocol based on unitary transformations of molecular orbitals to reduce the number of non-vanishing coefficients of spin-adapted configuration interaction expansions. Methods that exploit the sparsity of the Hamiltonian matrix and compactness of its eigensolutions, such as the FCIQMC algorithm in its spin-adapted implementation, are well suited to this protocol. The wave function compression resulting from this approach is particularly attractive for anti-ferromagnetically coupled polynuclear spin systems, such as transition metal cubanes in bio-catalysis and, Mott and charge-transfer insulators in solid state physics. Active space configuration interaction calculations on the stretched N2 and square N4 compounds, the chromium dimer, and a [Fe2S2] model system are presented as a proof-of-concept. For the Cr2 case large and intermediate bond distances are discussed, showing that the approach is effective in cases where static and dynamic correlation are equally important. The [Fe2S2] case shows the general applicability of the method.