title: Modelling the chemistry of Mn-doped MgO for bulk and (100) surfaces.
abstract: We have investigated the energetic properties of Mn-doped MgO bulk and (100) surfaces using a QM/MM embedding computational method, calculating the formation energy for doped systems, as well as for surface defects, and the subsequent effect on chemical reactivity. Low-concentration Mn doping is endothermic for isovalent species in the bulk but exothermic for higher oxidation states under p-type conditions, and compensated by electrons going to the Fermi level rather than cation vacancies. The highest occupied dopant Mn 3d states are positioned in the MgO band gap, about 4.2 eV below the vacuum level. Surface Mn-doping is more favourable than subsurface doping, and marginally exothermic on a (100) surface at high O2pressures. For both types of isovalent Mn-doped (100) surfaces, the formation energy for catalytically important oxygen defects is less than for pristine MgO, with F0and F2+-centres favoured in n- and p-type conditions, respectively. In addition, F+-centres are stabilised by favourable exchange coupling between the Mn 3d states and the vacancy-localised electrons, as verified through calculation of the vertical ionisation potential. The adsorption of CO2on to the pristine and defective (100) surface is used as a probe of chemical reactivity, with isovalent subsurface Mn dopants mildly affecting reactivity, whereas isovalent surface-positioned Mn strongly alters the chemical interactions between the substrate and adsorbate. The differing chemical reactivity, when compared to pristine MgO, justifies further detailed investigations for more varied oxidation states and dopant species.
authors.affiliation: Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK. a.logsdail@ucl.ac.uk and Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff, CF10 3AT, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Logsdail
authors.affiliation: Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK. a.logsdail@ucl.ac.uk and Scientific Computing Department, STFC Daresbury Laboratory, Daresbury, Warrington, WA4 4AD, UK.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Downing
authors.affiliation: Scientific Computing Department, STFC Daresbury Laboratory, Daresbury, Warrington, WA4 4AD, UK.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Keal
authors.affiliation: Scientific Computing Department, STFC Daresbury Laboratory, Daresbury, Warrington, WA4 4AD, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Sherwood
authors.affiliation: Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK. a.logsdail@ucl.ac.uk.
authors.forename: Alexey A
authors.identifier: http://orcid.org/0000-0003-0178-1147
authors.initials: AA
authors.lastname: Sokol
authors.affiliation: Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK. a.logsdail@ucl.ac.uk and Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff, CF10 3AT, UK and UK Catalysis Hub, Research Complex at Harwell, Science and Technology Facilities Council Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Oxon, OX11 0QX, UK.
authors.forename: C Richard A
authors.initials: CR
authors.lastname: Catlow