DFT Study of Alkali Metal Atom Adsorption on Defect-Free MgO(001) Surface

Abstract

The adsorption of isolated alkali metal atoms (Li, Na, K, Rb, and Cs) on defect-free surface of MgO(001) has been systemically investigated with density functional theory using a pseudopotential plane-wave approach. The adsorption energy calculated is about −0.72 eV for the lithium on top of the surface O site and about one third of this value for the other alkali metals. The relatively strong interaction of Li with the surface O can be explained by a more covalent bonding involved, evidenced by results of both the projected density of states and the charge density difference. The bonding mechanism is discussed in detail for all alkali metals.

Coordination chemistry insights into the role of alkali metal promoters in dinitrogen reduction

“…These thermodynamic data suggest that Li + forms stronger interactions with O-donor solvents. This is similar to one DFT study that calculated the free energy of alkali cation adsorption to an MgO surface, predicting that Li + binds more strongly ( E adsorption = −69.5 kJ/mol) than Na + , K + , Rb + , and Cs + ( E adsorption = −24.1 to −27.0 kJ/mol, no trend) to the metal oxide [62]. Since Li + is not a potent promoter of the H-B process and all other alkali cations have comparable adsorption free energies to MgO, it is unlikely that the binding energy of an alkali cation to the catalyst surface is a dominating factor towards the efficacy of that cation as a promoter.…”

Alkali metal atom adsorption on-top of the F s 0 defective center of MgO(001) surface

“…The trend of the decreasing adsorption energy from light atoms to heavy atoms except the cesium atom which will be discussed later is observed. It is similar to that of the alkali metal adsorbed above the oxygen anion on a clean terrace [19] . The adsorption energy is mainly determined by the interaction of the outmost orbits of the alkali metal atoms with the s-like orbit of oxygen vacancy.…”

Chemical Origin of Sodium Phosphate Interactions on Iron and Iron Oxide Surfaces by First Principle Calculations

“…There is no significant difference in the total charge transfer of Fe–Na 4 P 2 O 7 and Fe–Na 3 PO 4 systems, as their adsorption energies and interaction strength are similar. Additionally, no significant density difference is observed around sodium ions, as the alkali group is hard metals which usually interact through a weak polarization contribution . Consequently, Na only forms weak ionic bonds with its adjacent atoms such as oxygen or iron and results in the electron accumulation around Fe atoms (Fe5–Fe9) nearby due to the polarization effect from positive charged Na (Figure b,d and Table S2).…”

“…Additionally, no significant density difference is observed around sodium ions, as the alkali group is hard metals which usually interact through a weak polarization contribution. 46 Consequently, Na only forms a Δq 1 , Δq 2 , and Δq 3 are the absolute values of average charge transfer per atom in the first, second, and third layer, respectively. q Fe and q mol are the total charge transfer of the iron surface and alkali phosphate molecules, respectively.…”