Imperial College London

Dr Giuseppe Mallia

Faculty of Natural SciencesDepartment of Chemistry

Senior Teaching Fellow
 
 
 
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Contact

 

g.mallia

 
 
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Location

 

109Molecular Sciences Research HubWhite City Campus

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Summary

 

Publications

Publication Type
Year
to

35 results found

Savazzi F, Risplendi F, Mallia G, Harrison NM, Cicero Get al., 2018, Unravelling some of the structure-property relationships in graphene oxide at low degree of oxidation, Journal of Physical Chemistry Letters, Vol: 9, Pages: 1746-1749, ISSN: 1948-7185

Graphene oxide (GO) is a versatile 2D material whose properties can be tuned by changing the type and concentration of oxygen-containing functional groups attached to its surface. However, a detailed knowledge of the dependence of the chemo/physical features of this material on its chemical composition is largely unknown. We combine classical molecular dynamics and density functional theory simulations to predict the structural and electronic properties of GO at low degree of oxidation and suggest a revision of the Lerf–Klinowski model. We find that layer deformation is larger for samples containing high concentrations of epoxy groups and that correspondingly the band gap increases. Targeted chemical modification of the GO surface appears to be an effective route to tailor the electronic properties of the monolayer for given applications. Our simulations also show that the chemical shift of the C-1s XPS peak allows one to unambiguously characterize GO composition, resolving the peak attribution uncertainty often encountered in experiments.

Journal article

Wells MP, Zou B, Doiron BG, Kilmurray R, Mihai AP, Oulton RF, Gubeljak P, Ormandy K, Mallia G, Harrison N, Cohen LF, Maier S, Petrov PKet al., 2017, Tunable, Low Optical Loss Strontium Molybdate Thin Films for Plasmonic Applications, Advanced Optical Materials, Vol: 5, ISSN: 2195-1071

Strontium molybdate (SrMoO3) thin films are grown epitaxially on strontium titanate (SrTiO3), magnesium oxide (MgO), and lanthanum aluminate (LaAlO3) substrates by pulsed laser deposition and possess electrical resistivity as low as 100 µΩ cm at room temperature. SrMoO3 is shown to have optical losses, characterized by the product of the Drude broadening, ΓD, and the square of the plasma frequency, ωpu2, significantly lower than TiN, though generally higher than Au. Also, it is demonstrated that there is a zero-crossover wavelength of the real part of the dielectric permittivity, which is between 600 and 950 nm (2.05 and 1.31 eV), as measured by spectroscopic ellipsometry. Moreover, the epsilon near zero (ENZ) wavelength can be controlled by engineering the residual strain in the films, which arises from a strain dependence of the charge carrier concentration, as confirmed by density of states calculations. The relatively broad tunability of ENZ behavior observed in SrMoO3 demonstrates its potential suitability for transformation optics along with plasmonic applications in the visible to near infrared spectral range.

Journal article

Korotana RK, Mallia G, Fortunato NM, Amaral JS, Gercsi Z, Harrison NMet al., 2016, A combined thermodynamics and first principles study of the electronic, lattice and magnetic contributions to the magnetocaloric effect in La0.75Ca0.25MnO3, Journal of Physics D: Applied Physics, Vol: 49, ISSN: 0022-3727

Manganites with the formula La1−x Ca x MnO3 for 0.2  <  x  <  0.5 undergo a magnetic field driven transition from a paramagnetic to ferromagnetic state, which is accompanied by changes in the lattice and electronic structure. An isotropic expansion of the La0.75Ca0.25MnO3 cell at the phase transition has been observed experimentally. It is expected that there will be a large entropy change at the transition due to its first order nature. Doped lanthanum manganite (LMO) is therefore of interest as the active component in a magnetocaloric cooling device. However, the maximum obtained value for the entropy change in Ca-doped manganites merely reaches a moderate value in the field of a permanent magnet. The present theoretical work aims to shed light on this discrepancy. A combination of finite temperature statistical mechanics and first principles theory is applied to determine individual contributions to the total entropy change of the system by treating the electronic, lattice and magnetic components independently. Hybrid-exchange density functional (B3LYP) calculations and Monte Carlo simulations are performed for La0.75Ca0.25MnO3. Through the analysis of individual entropy contributions, it is found that the electronic and lattice entropy changes oppose the magnetic entropy change. The results highlighted in the present work demonstrate how the electronic and vibrational entropy contributions can have a deleterious effect on the total entropy change and thus the potential cooling power of doped LMO in a magnetocaloric device.

Journal article

Martínez-Casado R, Chen VH, Mallia G, Harrison NMet al., 2016, A hybrid-exchange density functional study of the bonding and electronic structure in bulk CuFeS2, Journal of Chemical Physics, Vol: 144, ISSN: 1089-7690

The geometric, electronic, and magnetic properties of bulk chalcopyrite CuFeS2 have been investigated using hybrid-exchange density functional theory calculations. The results are compared with available theoretical and experimental data. The theoretical description of the bonding and electronic structure in CuFeS2 is analyzed in detail and compared to those computed for chalcocite (CuS2) and greigite (Fe3S4). In particular, the behavior of the 3d electrons of Fe3+ is discussed in terms of the Hubbard-Anderson model in the strongly correlated regime and found to be similarly described in both materials by an on-site Coulomb repulsion (U) of ∼8.9 eV and a transfer integral (t) of ∼0.3 eV.

Journal article

Chen VH-Y, Mallia G, Martinez-Casado R, Harrison NMet al., 2015, Surface morphology of CuFeS2: The stability of the polar (112)/((112)over-bar) surface pair, Physical Review B, Vol: 92, ISSN: 1550-235X

The reconstruction and energetics for a range of chalcopyrite (CuFeS2) surfaces have been investigated using hybrid-exchange density functional theory. The stable nonpolar surfaces in increasing order of surface energy are (110), (102), and (114). In addition, the polar (112)/(112¯¯¯¯¯) surface pair was found to be remarkably stable with a surface formation energy that is only slightly higher than that of the (110) surface. The stability of (112)/(112¯¯¯¯¯) can be attributed to a combination of geometric and electronic mechanisms that result in the suppression of the electrostatic dipole perpendicular to the surface. Defect formation is a third mechanism that can further stabilize the (112)/(112¯¯¯¯¯) surface pair to an extent that it is thermodynamically preferred over the (110) surface. The stability of (112)/(112¯¯¯¯¯) means that regardless of the growth conditions, (112) and (112¯¯¯¯¯) facets are expected to have a significant presence in the surface morphology of CuFeS2.

Journal article

Ahmad EA, Tileli V, Kramer D, Mallia G, Stoerzinger KA, Shao-Horn Y, Kucernak AR, Harrison NMet al., 2015, Optimizing Oxygen Reduction Catalyst Morphologies from First Principles, Journal of Physical Chemistry C, Vol: 119, Pages: 16804-16810, ISSN: 1932-7455

Catalytic activity of perovskites for oxygen reduction (ORR) wasrecently correlated with bulk d-electron occupancy of the transition metal. Weexpand on the resultant model, which successfully reproduces the high activity ofLaMnO3 relative to other perovskites, by addressing catalyst surface morphology asan important aspect of the optimal ORR catalyst. The nature of reaction sites onlow index surfaces of orthorhombic (Pnma) LaMnO3 is established from FirstPrinciples. The adsorption of O2 is markedly influenced by local geometry andstrong electron correlation. Only one of the six reactions sites that result from experimentally confirmed symmetry-breakingJahn−Teller distortions is found to bind O2 with an intermediate binding energy while facilitating the formation of superoxide, animportant ORR intermediate in alkaline media. As demonstrated here for LaMnO3, rational design of the catalyst morphology topromote specific active sites is a highly effective optimization strategy for advanced functional ORR catalysts.

Journal article

Patel M, Sanches FF, Mallia G, Harrison NMet al., 2014, A quantum mechanical study of water adsorption on the (110) surfaces of rutile SnO2 and TiO2: investigating the effects of intermolecular interactions using hybrid-exchange density functional theory, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 16, Pages: 21002-21015, ISSN: 1463-9076

Journal article

Martinez-Casado R, Usvyat D, Mallia G, Maschio L, Casassa S, Ellis J, Schuetz M, Harrison NMet al., 2014, Diffraction of helium on MgO(100) surface calculated from first-principles, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 16, Pages: 21106-21113, ISSN: 1463-9076

Journal article

Sanches FF, Mallia G, Liborio L, Diebold U, Harrison NMet al., 2014, Hybrid exchange density functional study of vicinal anatase TiO2 surfaces, PHYSICAL REVIEW B, Vol: 89, ISSN: 2469-9950

Journal article

Martinez-Casado R, Usvyat D, Maschio L, Mallia G, Casassa S, Ellis J, Schuetz M, Harrison NMet al., 2014, Approaching an exact treatment of electronic correlations at solid surfaces: The binding energy of the lowest bound state of helium adsorbed on MgO(100), PHYSICAL REVIEW B, Vol: 89, ISSN: 2469-9950

Journal article

Korotana R, Mallia G, Gercsi Z, Liborio L, Harrison NMet al., 2014, Hybrid density functional study of structural, bonding, and electronic properties of the manganite series La1-xCaxMnO3 (x=0, 1/4, 1), PHYSICAL REVIEW B, Vol: 89, ISSN: 2469-9950

Journal article

Patel M, Mallia G, Harrison NM, 2013, The structure of water on rutile TiO2(110) for applications in solar hydrogen production: towards a predictive model using hybrid-exchange density functional theory, MRS Spring Meeting 2013

Conference paper

Korotana R, Mallia G, Gercsi Z, Harrison NMet al., 2013, A hybrid-exchange density functional study of Ca-doped LaMnO3, 12th Joint MMM-Intermag Conference, Publisher: AMER INST PHYSICS, ISSN: 0021-8979

Conference paper

Ahmad EA, Mallia G, Kramer D, Kucernak AR, Harrison NMet al., 2013, The stability of LaMnO3 surfaces: a hybrid exchange density functional theory study of an alkaline fuel cell catalyst, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 1, Pages: 11152-11162, ISSN: 2050-7488

Journal article

Risplendi F, Cicero G, Mallia G, Harrison NMet al., 2013, A quantum-mechanical study of the adsorption of prototype dye molecules on rutile-TiO2(110): a comparison between catechol and isonicotinic acid, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 15, Pages: 235-243, ISSN: 1463-9076

Journal article

Ahmad EA, Mallia G, Kramer D, Kucernak AR, Harrison NMet al., 2013, The stability of LaMnO3 surfaces: a hybrid exchange density functional theory study of an alkaline fuel cell catalyst (vol 1, pg 11152, 2013), JOURNAL OF MATERIALS CHEMISTRY A, Vol: 1, Pages: 15555-15555, ISSN: 2050-7488

Journal article

Patel M, Mallia G, Liborio L, Harrison NMet al., 2012, Water adsorption on rutile TiO2(110) for applications in solar hydrogen production: A systematic hybrid-exchange density functional study, PHYSICAL REVIEW B, Vol: 86, ISSN: 2469-9950

Journal article

Ahmad EA, Mallia G, Kramer D, Tileli V, Kucernak AR, Harrison NMet al., 2012, Comment on "2D Atomic Mapping of Oxidation States in Transition Metal Oxides by Scanning Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy", PHYSICAL REVIEW LETTERS, Vol: 108, ISSN: 0031-9007

Journal article

Ferretti A, Mallia G, Martin-Samos L, Bussi G, Ruini A, Montanari B, Harrison NMet al., 2012, Ab initio complex band structure of conjugated polymers: Effects of hydrid density functional theory and GW schemes, PHYSICAL REVIEW B, Vol: 85, ISSN: 2469-9950

Journal article

Ahmad EA, Liborio L, Kramer D, Mallia G, Kucernak AR, Harrison NMet al., 2011, Thermodynamic stability of LaMnO3 and its competing oxides: A hybrid density functional study of an alkaline fuel cell catalyst, PHYSICAL REVIEW B, Vol: 84, ISSN: 2469-9950

Journal article

Bush IJ, Tomic S, Searle BG, Mallia G, Bailey CL, Montanari B, Bernasconi L, Carr JM, Harrison NMet al., 2011, Parallel implementation of the ab initio CRYSTAL program: electronic structure calculations for periodic systems, PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 467, Pages: 2112-2126, ISSN: 1364-5021

Journal article

Scaranto J, Mallia G, Harrison NM, 2011, An efficient method for computing the binding energy of an adsorbed molecule within a periodic approach. The application to vinyl fluoride at rutile TiO2(110) surface, COMPUTATIONAL MATERIALS SCIENCE, Vol: 50, Pages: 2080-2086, ISSN: 0927-0256

Journal article

Liborio LM, Bailey CL, Mallia G, Tomic S, Harrison NMet al., 2011, Chemistry of defect induced photoluminescence in chalcopyrites: The case of CuAlS2, JOURNAL OF APPLIED PHYSICS, Vol: 109, ISSN: 0021-8979

Journal article

Martinez-Casado R, Mallia G, Usvyat D, Maschio L, Casassa S, Schuetz M, Harrison NMet al., 2011, Periodic quantum mechanical simulation of the He-MgO(100) interaction potential, JOURNAL OF CHEMICAL PHYSICS, Vol: 134, ISSN: 0021-9606

Journal article

Martinez-Casado R, Mallia G, Harrison NM, 2011, An alternative approach for the calculation of correlation energy in periodic systems: a hybrid MP2(B3LYP) study of the He-MgO(100) interaction, CHEMICAL COMMUNICATIONS, Vol: 47, Pages: 4385-4387, ISSN: 1359-7345

Journal article

Martinez-Casado R, Mallia G, Usvyat D, Maschio L, Casassa S, Schuetz M, Harrison NMet al., 2011, He-atom scattering from MgO(100): calculating diffraction peak intensities with a semi ab initio potential, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 13, Pages: 14750-14757, ISSN: 1463-9076

Journal article

Martinez-Casado R, Mallia G, Harrison NM, 2011, Ab initio calculation of the MgO(100) interaction with He and Ne: a HF+MP2 and HF+MP2(B3LYP) comparison, CHEMICAL COMMUNICATIONS, Vol: 47, Pages: 11630-11632, ISSN: 1359-7345

Journal article

Bailey CL, Liborio L, Mallia G, Tomic S, Harrison NMet al., 2010, Defect physics of CuGaS2, PHYSICAL REVIEW B, Vol: 81, ISSN: 2469-9950

Journal article

Bailey CL, Liborio L, Mallia G, Tomić S, Harrison NMet al., 2010, Calculating charged defects using CRYSTAL, Journal of Physics: Conference Series, Vol: 242, ISSN: 1742-6588

The methodology for the calculation of charged defects using the CRYSTAL program is discussed. Two example calculations are used to illustrate the methodology: He+ ions in a vacuum and two intrinsic charged defects, Cu vacancies and Ga substitution for Cu, in the chalcopyrite CuGaS2. © 2010 IOP Publishing Ltd.

Journal article

Liborio L, Mallia G, Harrison N, 2009, Electronic structure of the Ti4O7 Magneacuteli phase, PHYSICAL REVIEW B, Vol: 79, ISSN: 1098-0121

Journal article

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