Modeling spin Hamiltonian parameters for Fe2+ adatoms on Cu2N/Cu(100) surface: Semiempirical microscopic spin Hamiltonian approach

•Zero-field splitting parameters (ZFSPs) and g-factors modeled for Fe2+@Cu2N/Cu(100)•Crystal field and microscopic spin Hamiltonian theory (CF/MSH) approach employed.•Best set of spin-orbit, spin-spin (SS) coupling constants, CF 5D-levels determined.•For the first time 4th-rank ZFSPs B4q, g-factors, and SS-contributions considered.•EMR spectra simulations reveal importance of B4q and provide guidelines for HMF-EMR.•Results prove CF/MSH approach usefulness and applicability for other Fe2+ systems. Transition metal atoms adsorbed on surfaces (adatoms) behave like magnets in nanoscale and have potential applications in quantum computing. Scanning tunneling microscopy and inelastic tunneling spectroscopy studies yield the spin Hamiltonian parameters. Semi-empirical approach based on crystal-field and microscopic spin Hamiltonian theory is employed for modeling of the zero field splitting parameters bkq, and Zeeman g-factors for Fe2+(S = 2) adatoms on Cu2N/Cu(100) surface. These parameters are determined for wide ranges of the microscopic parameters: the spin-orbit (λ), spin-spin (ρ) coupling constants, and crystal-field energy levels (Di) within the 5D multiplet. Matching theoretical and experimental 2nd-rank parameters (b20, b22) yields suitable values of {λ, ρ, Di}. For the first time, also the 4th-rank parameters (b4q) as well as the g-factors and their ρ-contributions are estimated. Using EasySpin program we show that the transition energies and mixing coefficients obtained using only b2q differ significantly from those using both (b2q, b4q). This indicates that b4q significantly affect the spin energy levels. Hence interpretations of experimental data may be inaccurate if b4q are neglected. Our approach enables bridging the gap between semi-empirical and DFT/ab-initio methods and may be utilized for Fe2+(S = 2) adatoms on other surfaces and Fe2+-based molecular nanomagnets.