Exploring the impact of the nitrogen layer on a Cu(001) substrate on the spin crossover properties of [Fe(SalEen-I)2]Br: A DFT study

Abstract

This work investigates the impact of the Cu:N ratio in the nitrogen layer of a Cu(001) substrate coated with [Fe(SalEen-I)2]Br, an Fe(III) spin crossover (SCO) molecule. Specifically, we probe Cu/Cu(001), Cu3N/Cu(001), Cu2N/Cu(001), and CuN/Cu(001) substrates. To explore the molecule-substrate interaction, density functional theory calculations with Hubbard-U correction (DFT + U) and van der Waals interactions were conducted. From the analysis of the electronic structure, we propose that Cu2N/Cu(001) is the best candidate due to its weak chemical bonding to the adsorbed molecule and preservation of SCO bistability. Based on the total-energy calculations of various adsorption geometries and binding sites, the iodine atoms of the molecule adsorbed diagonally on copper atoms of the Cu2N(001) surface in the low-spin state is the most stable configuration. The energy difference between the high- and low-spin states of this configuration is 8.48 kJ/mol, which is significantly decreased compared to that of the free molecule of 29.14 kJ/mol.