The complete active space self-consistent field (CASSCF) method is successful at treating static correlation in molecular systems, however, it neglects dynamic correlation outside of the active space. Including dynamic correlation is essential for obtaining chemical accuracy, especially in systems where the active space is small relative to the size of the molecule. We are working on a density functional theory correction to the CASSCF method, with the goal of treating the core electrons with DFT and the active electrons with CASSCF. To do this, we are developing an LDA functional for the core electrons, which is based on uniform electron gas correlation energies. To obtain these correlation energies, we use the complete active space configuration interaction method on a variety of different electron gas system sizes and active space sizes, then correct for finite size effects by a combination of twist averaging and extrapolation.

Density functional theory correction to CASSCF

2019 Fall National Meeting

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