title: On the truncation of the number of excited states in density functional theory sum-over-states calculations of indirect spin spin coupling constants.
abstract: It is investigated, whether the number of excited (pseudo)states can be truncated in the sum-over-states expression for indirect spin-spin coupling constants (SSCCs), which is used in the Contributions from Localized Orbitals within the Polarization Propagator Approach and Inner Projections of the Polarization Propagator (IPPP-CLOPPA) approach to analyzing SSCCs in terms of localized orbitals. As a test set we have studied the nine simple compounds, CH4, NH3, H2O, SiH4, PH3, SH2, C2H2, C2H4, and C2H6. The excited (pseudo)states were obtained from time-dependent density functional theory (TD-DFT) calculations with the B3LYP exchange-correlation functional and the specialized core-property basis set, aug-cc-pVTZ-J. We investigated both how the calculated coupling constants depend on the number of (pseudo)states included in the summation and whether the summation can be truncated in a systematic way at a smaller number of states and extrapolated to the total number of (pseudo)states for the given one-electron basis set. We find that this is possible and that for some of the couplings it is sufficient to include only about 30% of the excited (pseudo)states.
authors.affiliation: Department of Physics, University of Northeastern - CONICET, Av. Libertad 5500, Corrientes W3404AAS, Argentina.
authors.forename: M Natalia C
authors.initials: MN
authors.lastname: Zarycz
authors.affiliation: Department of Physics, University of Northeastern - CONICET, Av. Libertad 5500, Corrientes W3404AAS, Argentina.
authors.forename: Patricio F
authors.initials: PF
authors.lastname: Provasi
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
authors.forename: Stephan P A
authors.initials: SP
authors.lastname: Sauer