School of Physical Sciences

Dr Maria Alfredsson

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Senior Lecturer in Theoretical Materials

Office: Room 217, Ingram Building
Telephone: (01227) 823237
Fax: 01227 827558 Email: m.l.alfredsson@kent.ac.uk

Functional Materials Group

 

Publications

 

Also view these in the Kent Academic Repository
Articles

    Alfredsson, L M and Canepa, P. and Ugliengo, P. (2012) Elastic and Vibrational Properties of a- and ß-PbO. Journal of Physical Chemistry C, 116 (40). pp. 21514-21522. ISSN 1932-7447.

    Abstract

    The structure, electronic, and dynamic properties of the two-layered ? (litharge) and ? (massicot) phases of PbO have been studied by density functional methods. The role of London dispersion interactions as leading component of the total interaction energy between layers has been addressed by using the Grimme’s approach in which new parameters for Pb and O atoms have been developed. Both gradient-corrected and hybrid functionals have been adopted using Gaussian-type basis sets of polarized triple-? quality for O atoms and small-core pseudopotential for the Pb atoms. Basis set superposition error (BSSE) has been accounted for by the Boys–Bernardi correction to compute the interlayer separation. Cross-checks with calculations adopting plane waves that are BSSE free have also been performed for both structures and vibrational frequencies. With the new set of proposed Grimme’s type parameters, structures and dynamical parameters for both PbO phases are in good agreement with experimental data.

    Canepa, P. and Schofield, E. and Chadwick, A.V. et al. (2011) Comparison of a calculated and measured XANES spectrum of ?-Fe2O3. Physical Chemistry Chemical Physics, 13 (28). pp. 12826-12834. ISSN 1463-9076.

    Abstract

    Comparison and prediction of the experimental XANES spectrum is a good measurement of the quality of the electronic structure calculations employed, and their ability to predict electronic transitions in solids. Here we present a comparison between BLYP + U and hybrid-BLYP calculations regarding the geometric, magnetic and electronic structures of ?-Fe2O3 (hematite). Several values of U and different percentages of Fock-exchange have been screened to see how their contributions affect different properties of hematite, paying particular attention to the electronic structure. To estimate the quality of the various methods the calculated density-of-states were compared to the experimentally collected XANES spectrum of the iron K-edge, providing information about the orbitals describing the conduction band. We find that in agreement with previous studies DFT + U and hybrid-functional simulations can correctly predict the character of the valence band, but only Fock-exchange higher than 30% or U-values equal or larger than 6 eV properly reproduce the order between the tg and e orbitals in the conduction band, and can, therefore, be used to study and predict XANES spectra and electronic transitions in hematite.

    Canepa, P. and Hanson, R. and Ugliengo, P. et al. (2011) J-ICE: a new Jmol interface for handling and visualizing crystallographic and electronic properties. Journal of Applied Crystallography, 44. pp. 225-229. ISSN 0021-8898.

    Abstract

    The growth in complexity of quantum mechanical software packages for modelling the physicochemical properties of crystalline materials may hinder their usability by the vast majority of non-specialized users. Consequently, a free operating-system-independent graphical user interface (GUI) has been developed to drive the most common simulation packages for treating both molecules and solids. In order to maintain maximum portability and graphical efficiency, the popular molecular graphics engine Jmol, written in the portable Java language, has been combined with a specialized GUI encoded in HTML and JavaScript. This framework, called J-ICE, allows users to visualize, build and manipulate complex input or output results (derived from modelling) entirely via a web server, i.e. without the burden of installing complex packages. This solution also dramatically speeds up both the development procedure and bug fixing. Among the range of software appropriate for modelling condensed matter, the focus of J-ICE is currently only on CRYSTAL09 and VASP.

    Kossoff, D. and Hudson-Edwards, K.A. and Dubbin, W.E. et al. (2008) Incongruent weathering of Cd and Zn from mine tailings. Mineralogical Magazine, 72 (1). pp. 81-84. ISSN 0026-461X.

    Abstract

    Weathering of discharged mine tailings contaminates streams, rivers and floodplains with toxic metals on a vast scale. The magnitude of the problem depends on input tailings mineralogy, storage and dispersal, and climatic conditions. To better understand the mechanisms of long-term tailings weathering, a leaching column study was established, incorporating tailings and soil from Potosi, Bolivia, with the aim of modelling a 25 year field period. The Zn/Cd molar ratio of the tailings leachate water, initially 738 for the unaltered tailings, is highly variable over 15 model years of leaching, particularly in the mixed tailings-soil columns. Columns with soil have ratios as high as 2563, while pure tailings columns reach ratios of <376. We employ complementary techniques, involving atomistic computational modelling, leachate analysis and mineralogical characterization, to elucidate the mechanisms governing these incongruent Cd and Zn weathering dynamics.

    Ono, Shigeaki and Brodholt, J.P. and Alfe, Dario et al. (2008) Ab initio molecular dynamics simulations for thermal equation of state of B2-type NaCl. Journal of Applied Sciences, 103 (2). pp. 023510. ISSN 0021-8979.

    Abstract

    The pressure as a function of volume and temperature has been investigated for B2-type NaCl over the pressure range of 20-360 GPa and at temperatures between 300 and 3000 K. The simulations were performed using ab initio molecular dynamics method within the density-functional theory framework. A Vinet equation of state fitted to the 300 K data yielded a bulk modulus of B(Ta)=128.66 GPa and a pressure derivative of B(Ta)'=4.374 at standard state pressure of 30 GPa. The thermal pressure contribution was determined to be of the form Delta P(th)=[alpha B(T)(V(a))+(partial derivative B(T)/partial derivative T)(V) ln(V(a)/V)]Delta T. When alpha B(T)(V(a)) is assumed to be constant, the fit to the data yielded alpha B(T)(V(a))=0.0033 GPa/K at standard volume, corresponding to the pressure of 30 GPa. In contrast, the volume dependence of the thermal pressure was very small, and fitting yielded (partial derivative B(T)/partial derivative T)(V)=0.000 87.

Total publications in KAR: 34 [See all in KAR]
 

School of Physical Sciences, Ingram Building, University of Kent, Canterbury, Kent, CT2 7NH

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Last Updated: 27/02/2013