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A RASSCF study of free base, magnesium and zinc porphyrins: accuracy versus efficiency

Research output: Contribution to Journal/MagazineJournal articlepeer-review

<mark>Journal publication date</mark>14/02/2013
<mark>Journal</mark>Physical Chemistry Chemical Physics
Issue number6
Number of pages13
Pages (from-to)2197-2209
Publication StatusPublished
<mark>Original language</mark>English


The restricted-active-space self-consistent-field methodology is successfully applied to the study of free base-and regular metalloporphyrins, the latter containing magnesium and zinc central ions. It is shown that inclusion of all excitations involving the Gouterman frontier orbitals in the RAS2 subspace results in a numerically stable approach, producing highly accurate results at a fraction of the computational cost of the complete-active-space self-consistent-field method, whereas increasing RAS2 beyond this size leads to only modest improvement. Topological and orbital analysis shows that the approach is also able to give a highly accurate description of the electronic wavefunction. Inclusion of the entire p-conjugated subsystem in the active space results in more accurate excitation energies and a reduction in the dependence on the exact form of the perturbational Hamiltonian used to include dynamic correlation. The larger active space also resolves a quantitative disagreement in results obtained with and without the inclusion of dynamic correlation.