Homonuclear 3d transition-metal diatomics: A systematic density functional theory study

Abstract

The equilibrium bond lengths, harmonic vibrational frequencies, and dissociation energies of the ground state homonuclear 3d transition-metal diatomics (scandium through copper) were determined using six density functional or hybrid Hartree–Fock/density functional theory (HF/DFT) methods and unrestricted Hartree–Fock theory. Results are compared to other theoretical studies and to experimental values when available. The accuracy of the DFT results is found to be highly dependent upon the functional employed, with the pure DFT methods, BLYP and BP86, often performing significantly better than the hybrid HF/DFT methods. For the van der Waals complex Mn2, all six functionals predict the ground state to be high-spin, disagreeing with experiment; the true (antiferromagnetic) ground state was not found for any functional. Average errors for theoretical geometries and vibrational frequencies are for B3LYP, 0.053 Å (2.4%) and 122 cm−1 (31.1%); for B3P86, 0.051 Å (2.4%) and 122 cm−1 (31.3%); for BHLYP, 0.077 Å (4.1%) and 208 cm−1 (49.3%); for BLYP, 0.024 Å (1.3%) and 98 cm−1 (24.5%); for BP86, 0.020 Å (1.1%) and 104 cm−1 (25.6%); and for LSDA, 0.056 Å (3.0%) and 158 cm−1 (37.9%). No functional gives results directly comparable for all nine species. Dissociation energy results are severely overestimated in many instances and negative in others. Anecdotal reports of success for density functional theory for these systems may have been overblown.

Theoretical DFT study of homonuclear and binary transition-metal dimers

“…They found that their theoretical results are dependent on the exchange-correlation (XC) functional used, suggesting that a systematic study is necessary to establish the best theoretical scheme as a requirement to gain basic knowledge of nanoparticle physicochemical properties. This remark is stressed by the results of comparative studies on first-row homonuclear TM dimers [17,18]. Several properties are calculated involving various XC functionals, which cast clear differences between each other in, for example, binding energies and equilibrium bond lengths.…”

Cobalt clusters (Con, n⩽6) and their anions

“…On the theoretical side, there are a number of investigations spreading the level of the theory from an evolutive algorithm based on the semi-empirical Gupta potential [14], to a tight-binding molecular dynamics [15], and pseudo-atomic [16][17][18][19][20] and allelectron density functional theory (DFT) calculations [21][22][23][24]. The available results in the literature are not in good agreement.…”

Electronic Structure and Reactivity of Transition Metal Complexes

“…A tradeoff between basis set size and active space size in early configuration interaction studies limited the accuracy of the relative energetics for the hundreds of states of various spins and symmetries considered [22,23]. Despite the need to reconsider the discrepancy between experimental and theoretical findings since the late 1970s, even recent comprehensive studies of transition metal diatomic molecules [24,27] continue to assume the 7 D u assignment to be the correct one for the ground state of iron dimer. There have, however, been some more recent high-level quantum chemistry calculations-multireference configuration interaction (MRCI) [28] as well as large basis set, single-reference coupled cluster [CCSD(T)] calculations [29]-which provide evidence for a more consistent alternative ground state 9 S À g for the iron dimer.…”