Assessment of TD-DFT and LF-DFT for study of d − d transitions in first row transition metal hexaaqua complexes

Abstract

Herein, we present the systematic, comparative computational study of the d - d transitions in a series of first row transition metal hexaaqua complexes, [M(H2O)6](n+) (M(2+/3+) = V (2+/3+), Cr(2+/3+), Mn(2+/3+), Fe(2+/3+), Co(2+/3+), Ni(2+)) by the means of Time-dependent Density Functional Theory (TD-DFT) and Ligand Field Density Functional Theory (LF-DFT). Influence of various exchange-correlation (XC) approximations have been studied, and results have been compared to the experimental transition energies, as well as, to the previous high-level ab initio calculations. TD-DFT gives satisfactory results in the cases of d(2), d(4), and low-spin d(6) complexes, but fails in the cases when transitions depend only on the ligand field splitting, and for states with strong character of double excitation. LF-DFT, as a non-empirical approach to the ligand field theory, takes into account in a balanced way both dynamic and non-dynamic correlation effects and hence accurately describes the multiplets of transition metal complexes, even in difficult cases such as sextet-quartet splitting in d(5) complexes. Use of the XC functionals designed for the accurate description of the spin-state splitting, e.g., OPBE, OPBE0, or SSB-D, is found to be crucial for proper prediction of the spin-forbidden excitations by LF-DFT. It is shown that LF-DFT is a valuable alternative to both TD-DFT and ab initio methods.

Structure and Electronic Properties of an Expanded Terpyridine Complex of Nickel(II) [Ni(ddpd)2](BF4)2

“…In a CASSCF(8,13) study of [Ni(H 2 O) 6 ] 2+ by Reber and co‐workers, only the energies of the triplet states were reported and hence a comparison concerning the accuracy of relative energies of singlet and triplet states in octahedral Ni II complexes is impossible . A further improvement concerning the accuracy of calculated transition energies may be achieved by ligand field DFT calculations, which gave good results for hexaaqua complexes of 3d metal ions V 2+/3+ ‐Ni 2+ …”

Combined Experimental and Theoretical Investigation of the Origin of Magnetic Anisotropy in Pentagonal Bipyramidal Isothiocyanato Co(II), Ni(II), and Fe(III) Complexes with Quaternary-Ammonium-Functionalized 2,6-Diacetylpyridine Bisacylhydrazone

“…LFDFT includes both dynamical correlation (through the DFT exchange-correlation energy) and non-dynamical correlation (via LF Configuration Interaction). With LFDFT procedure, all customary molecular properties can be calculated, [88][89][90][91][92][93][94] including ZFS parameters, 19,20,95,96 however, its accuracy decreases with increasing metal-ligand covalency. 97 Comparison between experimentally determined and calculated ZFS parameters in PBPY-7…”

Assessing Excited State Energy Gaps with Time-Dependent Density Functional Theory on Ru(II) Complexes

“…1 In Ref. 30, a systematic evaluation of the d-d transitions in aquated ion complexes using TD-DFT and Ligand Field DFT is provided. Many of the transition metal complex benchmarks consider a specific collection of transition metal complexes with a given motif.…”