Performance of the B3LYP/ECP DFT Calculations of Iron-Containing Compounds

Abstract

Iron-containing molecules and ions with various types of bonding were calculated using DFT theory (B3LYP functional) and an energy-adjusted effective core potential for iron (ECP(S)). Examination of calculated geometries, bond dissociation energies, ionization energies, enthalpies of formation, and harmonic frequencies and their comparison with experimental and higher level (CCSD(T), MCPF, CASSCF) computational data show that B3LYP/ECP(S) calculations of iron-containing species are capable of giving reliable results. The dissociation energies were calculated for iron-containing species with various bonding interactions having experimental estimates of bond strengths varying from 5.0 (Fe+−H2) to 99.5 kcal/mol (Fe+−CH), i.e., within a range of 95 kcal/mol, do not reveal any systematic trends in the errors. The average absolute deviation is 4.6 kcal/mol. The maximum deviation from the experimental D 0 value is +8.0 kcal/mol for Fe+−CH. This experimental estimate, however, has an uncertainty of ±7 kcal/mol. The B3LYP/ECP(S) calculated enthalpies of formation have an average absolute deviation of 5.7 kcal/mol with the largest deviation of 14 ± 7 kcal/mol of the experimental ΔH f 0 value in the case of FeCH+. Geometries and harmonic frequencies calculated using the B3LYP/ECP(S) scheme are generally in good agreement with the available experimental data or with results of higher level calculations.

Solvent and Ligand Effects on the Structures of Iron Halide Cations in the Gas Phase

“…Given the qualitative nature of the AE measurements, we note in passing that the experimental values for the unsolvated species are in rather good agreement with values reported in the literature (FeF + : 4.5; FeCl + : 3.5; FeBr + : 2.7; FeI + : 2.6 eV). [19][20][21][22][23] Further, the binding energies for the cleavage of the Fe-X-bonds also increase with solvation, the origin of which has been discussed previously. [15] If solvated with only one or two methanol molecules, the FFe(CH 3 OH) n + ions exhibit elimination of HF as yet another fragmentation channel.…”

Assignment of the Photoelectron Spectra of FeS3– by Density Functional Theory, CASPT2, and RCCSD(T) Calculations

“…23 Our calculations therefore used this functional with the QZVP basis set 24 to obtain the equilibrium structures of all lowlying spin multiplicities of these clusters. Geometries of FeS 3 0/À were optimized within the spin-unrestricted self-consistent field (SCF) scheme by applying no spatial symmetry constraints.…”

Vibrational spectroscopy of intermediates in benzene-to-pheno conversion by FeO+

“…Calculations at the B3LYP/6-311ϩG(d,p) level incorrectly predict a quartet ground state, 19.8 kJ/mol below the sextet state. This is a well known failure of the B3LYP method [24,25]. An attractive alternative to rigorous and expensive high level correlated ab initio calculations are hybrid methods developed for accurate thermochemistry, such as the complete basis set CBS-QB3 approach [22,23].…”