Joseph Muscat | Henley Business School (original) (raw)

Papers by Joseph Muscat

Surface Science, 2002

Adhesion between clean, bulk-terminated bcc Fe(1 0 0) and Fe(1 1 0) matched and mismatched surfac... more Adhesion between clean, bulk-terminated bcc Fe(1 0 0) and Fe(1 1 0) matched and mismatched surfaces was simulated within the theoretical framework of the density functional theory. The generalized-gradient spin approximation exchange-correlation functional was used in conjunction with a plane wave-ultrasoft pseudopotential representation. The structure and properties of bulk bcc Fe were calculated in order to establish the reliability of the methodology employed, as well as to determine suitably converged values of computational parameters to be used in subsequent surface calculations. Interfaces were modelled using a single supercell approach, with the interfacial separation distance manipulated by the size of vacuum separation between vertically adjacent surface cells. The adhesive energies at discrete interfacial separations were calculated for each interface and the resulting data fitted to the universal binding energy relation (UBER) of Rose et al. [Phys. Rev. Lett. 47 (1981) 675]. An interpretation of the values of the fitted UBER parameters for the four Fe interfaces studied is given. In addition, a discussion on the validity of the employed computational methodology is presented.

Molecular Simulation, 2002

We benchmark the performance of four treatments of electron exchange and correlation in the predi... more We benchmark the performance of four treatments of electron exchange and correlation in the prediction of structural and elastic properties of a range of minerals. The treatments used are the Hartree–Fock (HF) theory, the local density approximation (LDA) and the generalised ...

Surface Science, 2003

Photoelectron spectroscopy has been employed to probe the electronic structure of TiO 2 (1 0 0)c(... more Photoelectron spectroscopy has been employed to probe the electronic structure of TiO 2 (1 0 0)c(2 • 2)K. In sharp contrast to earlier work, no features indicating the presence of Ti 3þ cations are found in the photoelectron spectra. This unexpected result is rationalised on the basis of ab initio periodic slab calculations. These calculations demonstrate that in this system K is fully ionised (K fi K þ), and that the majority of the charge transferred across the TiO 2 /K interface resides on Ti cations, reducing them formally from Ti 4þ to Ti 3þ. However, the excess charge is not restricted to near surface Ti ions, but rather can occupy any Ti site throughout the bulk, and so is unobservable by photoelectron spectroscopy, due to the negligible concentration of Ti 3þ cations in the surface region.

Surface Science, 2000

... Permissions & Reprints. The physical and electronic structure of the rutile (001)... more ... Permissions & Reprints. The physical and electronic structure of the rutile (001) surface. J. Muscat and NM Harrison Corresponding Author Contact Information , E-mail The Corresponding Author. CLRC Daresbury Laboratory, Daresbury, Warrington WA4 4AD, UK. ...

Surface Science, 2002

We have performed density-functional theory calculations using both plane wave-pseudopotential an... more We have performed density-functional theory calculations using both plane wave-pseudopotential and Gaussian basis set approaches on the (1 0 0), planar (1 1 0) and microfacetted (1 1 0) surfaces of pyrite (FeS 2). Our calculations indicate that the (1 0 0) surface is more stable than the planar (1 1 0) surface, which is predicted to have a higher surface energy. Creation of microfacets on the (1 1 0) surface resulted in a lower surface energy. Relatively small differences in calculated surface energy between the ideal and relaxed (1 0 0) and (1 1 0) surfaces were found. The (1 0 0) and (1 1 0) surfaces are predicted to be essentially bulk-terminated, with a relatively small amount of relaxation. Electrostatic effects induced by loss of coordination at surface Fe atoms are likely to be responsible for surface ionic displacements. Our calculations indicate that surface Fe atoms of fourfold coordination, present on the (1 1 0) surfaces, are spin polarized, while those of fivefold coordination are fully spin-paired. These results suggest that magnetic species, such as O 2 , are more prone to react at low Fe coordination defect sites on real FeS 2 (1 0 0) surfaces.

Physical Review B, 2005

The electron structure, magnetic, structural, and elastic properties of ilmenite ͑FeTiO 3 ͒ are c... more The electron structure, magnetic, structural, and elastic properties of ilmenite ͑FeTiO 3 ͒ are computed within a hybrid density functional formalism. The computed properties are found to be very sensitive to the treatment of electronic exchange and correlation; Hartree-Fock and generalized gradient approximation calculations are performed for comparison. Within the hybrid formalism a qualitatively correct description of the ground-state electronic structure is obtained. Predicted geometric and elastic parameters are in close agreement with experiment as is the charge transfer excitation energy. The essential features of this functional are its treatment of the electronic self interaction and its reasonable estimate of the pair correlation energy of the doubly occupied Fed orbital.

Geochimica et Cosmochimica Acta, 2003

Faraday Discussions, 1997

Faraday Discussions, 1999

Chemical Physics Letters, 2001

... Indeed it is clear that corrections to the current functional are likely to worsen the corres... more ... Indeed it is clear that corrections to the current functional are likely to worsen the correspondence. ... Neverthless, it is clear that in studies of the variation of the band gap with, for instance, chemical composition or structure the current approach provides an extremely useful ...

Surface Science, 2001

The results of a study of the physical, elastic and electronic properties of PbS using both ®rst ... more The results of a study of the physical, elastic and electronic properties of PbS using both ®rst principles theoretical and experimental X-ray and ultraviolet photoelectron techniques are presented. We have investigated the in¯uence of the computational approximations such as the basis set, pseudopotential and the treatment of exchange and correlation on the accuracy of the theoretical results. The current study work con®rms that the binding energy of the S 3s state lies at 13 eV, in agreement with previous experimental work and contrary to earlier ab initio Hartree±Fock (HF) calculations. We establish that the reason for the discrepancy between previous experimental and theoretical determinations of the electronic structure of PbS is due to the treatment of the exchange interaction. We demonstrate that calculations using the HF approximation tend to overestimate the binding energies of the valence and core states yielding densities of states in poor agreement with experiment whereas calculations performed with density functional theory within either the local density or the generalised gradient approximation give a signi®cantly better description of the electronic structure. Finally, we con®rm that hybrid functional techniques such as B3LYP provide an excellent description of the physical and electronic structure of PbS.

Surface Science, 2002

Adhesion between clean, bulk-terminated bcc Fe(1 0 0) and Fe(1 1 0) matched and mismatched surfac... more Adhesion between clean, bulk-terminated bcc Fe(1 0 0) and Fe(1 1 0) matched and mismatched surfaces was simulated within the theoretical framework of the density functional theory. The generalized-gradient spin approximation exchange-correlation functional was used in conjunction with a plane wave-ultrasoft pseudopotential representation. The structure and properties of bulk bcc Fe were calculated in order to establish the reliability of the methodology employed, as well as to determine suitably converged values of computational parameters to be used in subsequent surface calculations. Interfaces were modelled using a single supercell approach, with the interfacial separation distance manipulated by the size of vacuum separation between vertically adjacent surface cells. The adhesive energies at discrete interfacial separations were calculated for each interface and the resulting data fitted to the universal binding energy relation (UBER) of Rose et al. [Phys. Rev. Lett. 47 (1981) 675]. An interpretation of the values of the fitted UBER parameters for the four Fe interfaces studied is given. In addition, a discussion on the validity of the employed computational methodology is presented.

Molecular Simulation, 2002

We benchmark the performance of four treatments of electron exchange and correlation in the predi... more We benchmark the performance of four treatments of electron exchange and correlation in the prediction of structural and elastic properties of a range of minerals. The treatments used are the Hartree–Fock (HF) theory, the local density approximation (LDA) and the generalised ...

Surface Science, 2003

Photoelectron spectroscopy has been employed to probe the electronic structure of TiO 2 (1 0 0)c(... more Photoelectron spectroscopy has been employed to probe the electronic structure of TiO 2 (1 0 0)c(2 • 2)K. In sharp contrast to earlier work, no features indicating the presence of Ti 3þ cations are found in the photoelectron spectra. This unexpected result is rationalised on the basis of ab initio periodic slab calculations. These calculations demonstrate that in this system K is fully ionised (K fi K þ), and that the majority of the charge transferred across the TiO 2 /K interface resides on Ti cations, reducing them formally from Ti 4þ to Ti 3þ. However, the excess charge is not restricted to near surface Ti ions, but rather can occupy any Ti site throughout the bulk, and so is unobservable by photoelectron spectroscopy, due to the negligible concentration of Ti 3þ cations in the surface region.

Surface Science, 2000

... Permissions & Reprints. The physical and electronic structure of the rutile (001)... more ... Permissions & Reprints. The physical and electronic structure of the rutile (001) surface. J. Muscat and NM Harrison Corresponding Author Contact Information , E-mail The Corresponding Author. CLRC Daresbury Laboratory, Daresbury, Warrington WA4 4AD, UK. ...

Surface Science, 2002

We have performed density-functional theory calculations using both plane wave-pseudopotential an... more We have performed density-functional theory calculations using both plane wave-pseudopotential and Gaussian basis set approaches on the (1 0 0), planar (1 1 0) and microfacetted (1 1 0) surfaces of pyrite (FeS 2). Our calculations indicate that the (1 0 0) surface is more stable than the planar (1 1 0) surface, which is predicted to have a higher surface energy. Creation of microfacets on the (1 1 0) surface resulted in a lower surface energy. Relatively small differences in calculated surface energy between the ideal and relaxed (1 0 0) and (1 1 0) surfaces were found. The (1 0 0) and (1 1 0) surfaces are predicted to be essentially bulk-terminated, with a relatively small amount of relaxation. Electrostatic effects induced by loss of coordination at surface Fe atoms are likely to be responsible for surface ionic displacements. Our calculations indicate that surface Fe atoms of fourfold coordination, present on the (1 1 0) surfaces, are spin polarized, while those of fivefold coordination are fully spin-paired. These results suggest that magnetic species, such as O 2 , are more prone to react at low Fe coordination defect sites on real FeS 2 (1 0 0) surfaces.

Physical Review B, 2005

The electron structure, magnetic, structural, and elastic properties of ilmenite ͑FeTiO 3 ͒ are c... more The electron structure, magnetic, structural, and elastic properties of ilmenite ͑FeTiO 3 ͒ are computed within a hybrid density functional formalism. The computed properties are found to be very sensitive to the treatment of electronic exchange and correlation; Hartree-Fock and generalized gradient approximation calculations are performed for comparison. Within the hybrid formalism a qualitatively correct description of the ground-state electronic structure is obtained. Predicted geometric and elastic parameters are in close agreement with experiment as is the charge transfer excitation energy. The essential features of this functional are its treatment of the electronic self interaction and its reasonable estimate of the pair correlation energy of the doubly occupied Fed orbital.

Geochimica et Cosmochimica Acta, 2003

Faraday Discussions, 1997

Faraday Discussions, 1999

Chemical Physics Letters, 2001

... Indeed it is clear that corrections to the current functional are likely to worsen the corres... more ... Indeed it is clear that corrections to the current functional are likely to worsen the correspondence. ... Neverthless, it is clear that in studies of the variation of the band gap with, for instance, chemical composition or structure the current approach provides an extremely useful ...

Surface Science, 2001

The results of a study of the physical, elastic and electronic properties of PbS using both ®rst ... more The results of a study of the physical, elastic and electronic properties of PbS using both ®rst principles theoretical and experimental X-ray and ultraviolet photoelectron techniques are presented. We have investigated the in¯uence of the computational approximations such as the basis set, pseudopotential and the treatment of exchange and correlation on the accuracy of the theoretical results. The current study work con®rms that the binding energy of the S 3s state lies at 13 eV, in agreement with previous experimental work and contrary to earlier ab initio Hartree±Fock (HF) calculations. We establish that the reason for the discrepancy between previous experimental and theoretical determinations of the electronic structure of PbS is due to the treatment of the exchange interaction. We demonstrate that calculations using the HF approximation tend to overestimate the binding energies of the valence and core states yielding densities of states in poor agreement with experiment whereas calculations performed with density functional theory within either the local density or the generalised gradient approximation give a signi®cantly better description of the electronic structure. Finally, we con®rm that hybrid functional techniques such as B3LYP provide an excellent description of the physical and electronic structure of PbS.