The electronic configurations of LnX (Ln = La–Eu, X = O, S, Se, Te): A FON–DFT investigation

Abstract

Relativistic density functional theory calculation has been carried out for lanthanide monochalcogenide molecules LnX (Ln=La–Eu, X=O, S, Se, Te). Fractional occupation number approach was applied to investigate the electronic structure. LnX are mainly ionic molecules with 5d–np (n=2–5 for O–Te) covalent contributions. The ground state formal configuration is 4fkσ1 (k=0–6 for La–Eu) when k<3, and 4fk+1σ0 when k>3. NdX (k=3) molecules mostly behave as a mixture between them. Molecular orbital analysis and Mulliken population indicate orbital mixing of Ln (4f, 5d, 6s) in most molecules. Spin–orbit coupling has an increasing effect from La to Eu on bond lengths and dipole moments.