Geometries and electronic states of iron trimer (Fe3) by CCSD and CCSD(T) calculations

Tetsuya Nakazawa

doi:10.1063/5.0052065

Abstract

Geometries and energy separations of various low-lying electronic states of an iron trimer (Fe3) are investigated by coupled-cluster singles and doubles (CCSD) and coupled-cluster singles and doubles plus perturbative triples [CCSD(T)] calculations. The ground state is found to be a 13A′ state with Cs symmetry, whereas a nearly isoenergetic state, 13A1 (C2v), is degenerate to the ground state. The ground and five low-lying states with a spin multiplicity of 13 are found below 0.20 eV at the CCSD(T) level. On the other hand, the low-lying states with spin multiplicities of 9, 11, and 15 appear only above 0.20 eV. From detailed natural bond orbital analyses, Fe3 has Fe–Fe bonds composed of σ-bond orbitals only in theβ-spin part with higher s-character in low-lying states with a spin multiplicity of 13. The polarization coefficients indicate that the σFe–Fe bonds are nearly complete covalent bonds with little polarization.

Highlights

An understanding of geometric and electronic properties of transition metal (TM) clusters is useful for technological applications, such as catalysis1–3 and ultra-high density magnetic storage devices.4–6 TM clusters, especially iron clusters, have been still a challenging subject even though they have been studied experimentally and theoretically for many years
The formation of Fe3 has been confirmed in the Mössbauer studies of Fe–X (M = Cu, Co, Mn, and Sn)7–11 and pure Fe clusters12 isolated in a rare gas matrix, suggesting that the geometry is a triangle
The coupled-cluster singles and doubles (CCSD)(T)/6-311+G(d) single point energy calculations are performed with the CCSD(T)/6-31+G(d) optimized geometries to validate the ordering of relative energies in different spin states

Summary

Introduction

An understanding of geometric and electronic properties of transition metal (TM) clusters is useful for technological applications, such as catalysis and ultra-high density magnetic storage devices. TM clusters, especially iron clusters, have been still a challenging subject even though they have been studied experimentally and theoretically for many years. TM clusters, especially iron clusters, have been still a challenging subject even though they have been studied experimentally and theoretically for many years. Even the ground states of small iron clusters are not yet fully understood. Many experimental studies have reported the existence of iron trimer (Fe3) clusters. The formation of Fe3 has been confirmed in the Mössbauer studies of Fe–X (M = Cu, Co, Mn, and Sn) and pure Fe clusters isolated in a rare gas matrix, suggesting that the geometry is a triangle. The infrared spectra of Fe clusters in the Ar matrix at 12 K have shown that Fe3 has a C2v triangular geometry.. The resonance Raman spectra have indicated that mass-selected Fe3 in the Ar matrix is a Jahn–Teller distorted triangular molecule.. The infrared spectra of Fe clusters in the Ar matrix at 12 K have shown that Fe3 has a C2v triangular geometry. The resonance Raman spectra have indicated that mass-selected Fe3 in the Ar matrix is a Jahn–Teller distorted triangular molecule. The spin multiplicity of Fe3 has been deduced to be 9 from a Stern–Gerlach magnetic deflection experiment.

Methods

Results

Conclusion