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Charles Patterson
Associate Professor, Physics

Biography

1982 B.Sc. (Hons.) in Chemistry, University of Bristol. 1982-85 PhD in Chemistry, University of Cambridge. PhD topic: Reactions at single crystal surfaces. 1986-90 Postdoctoral Fellow, University of Pennsylvania. Research topics: Electron energy loss spectroscopy and X ray photoelectron spectroscopy. Ab initio computational studies of surfaces and clusters. 1987 Visiting researcher A.T. and T. Bell Laboratories, Murray Hill, New Jersey. Research topic: Low energy ion scattering from NiAl(110). 1990 Postdoctoral Research Fellow, Department of Physics, TCD. Ab initio computational studies of optical properties of semiconductor surfaces. 1991-04 Lecturer in Science of Materials, Department of Physics,TCD. Research Interests: Computational materials science. 1997-11 Director of Computational Physics Degree Course, TCD. 2004-current Senior Lecturer/Associate Professor, Department of Physics, TCD.

Publications and Further Research Outputs

Peer-Reviewed Publications

P. Kumar and C. H. Patterson, Dielectric anisotropy of the GaP/Si(001) interface from first-principles theory, Physical Review Letters, 118, 2017, pin press- Journal Article, 2017

E. Mehes and C. H. Patterson, Defects at the Si(001)/a-SiO2 interface: Analysis of structures generated with classical force fields, Physical Review Materials, 2017 Journal Article, 2017

S. Banerjee, C. H. Patterson and J. F. McGilp, Group V adsorbate structure on vicinal Ge(001) surfaces determined from the optical spectrum, Applied Physics Letters, 2017, pin press- Journal Article, 2017

C. H. Patterson, S. Banerjee, J. F. McGilp, Reflectance anisotropy spectroscopy of the Si(111)-(5 × 2)Au surface, Physical Review B, 94, (15/16), 2016, p165417 - 9 pages Journal Article, 2016 URL

C. H. Patterson, Atomic and electronic structures of Si(111)-(√3x√3)R30-Au and (6x6)-Au surfaces, Journal of Physics Condensed Matter, 27, 2015, p475001- Journal Article, 2015 URL DOI

Banerjee, S., McGilp, J.F., Patterson, C.H., Reflectance anisotropy spectroscopy of clean and Sb covered Ge(001) surfaces and comparison with clean Si(001) surfaces, Physica Status Solidi (B) Basic Research, 252, (1), 2015, p78 - 86 Journal Article, 2015 DOI

P. Kumar and C. H. Patterson, Reflectance anisotropy of the anatase TiO2(001)-(4x1) surface, J. Phys. Condens. Matter, 26, (44), 2014, p445006 1-6 Journal Article, 2014 URL

C. H. Patterson, Hybrid DFT calculation of 57Fe NMR resonances and orbital order in magnetite , Physical Review B, 90, (7), 2014, p075134 1-11 Journal Article, 2014 URL TARA - Full Text

Jorgji, S., McGilp, J.F., Patterson, C.H., Reflectance anisotropy spectroscopy of Si(111)-(3×1)Li and Ag surfaces, Physical Review B - Condensed Matter and Materials Physics, 87, (19), 2013, part. no. 195304 Journal Article, 2013 TARA - Full Text DOI

Jorgji, S, McGilp, JF, Patterson, CH, Reflectance anisotropy spectroscopy of Si(111)-(3 x 1)Li and Ag surfaces, PHYSICAL REVIEW B, 87, (19), 2013 Journal Article, 2013 TARA - Full Text DOI

Charles H. Patterson, High resolution electron energy loss spectroscopy of clean and hydrogen covered Si(001) surfaces: First principles calculations , Journal of Chemical Physics, 137, (9), 2012, p094701-1 - 094701-10 Journal Article, 2012 TARA - Full Text DOI URL

Aurab Chakrabarty and Charles H. Patterson, Transition levels of defects in ZnO: Total energy and Janak's theorem methods , Journal of Chemical Physics, 137, 2012, p054709-1 - 054709-6 Journal Article, 2012 DOI TARA - Full Text URL

Charles H. Patterson, Validity of the HREELS surface dipole selection rule at semiconductor surfaces: Si(001)-(2x1)H/D, EPL, 98, 2012, p66001-1 - 66001-5 Journal Article, 2012 URL DOI

Chakrabarty, A, Patterson, CH, Defect-trapped electrons and ferromagnetic exchange in ZnO, PHYSICAL REVIEW B, 84, (5), 2011 Journal Article, 2011 TARA - Full Text

C. H. Patterson, S. Banerjee, J. F. McGilp, Optical and phonon excitations of modified Pandey chains at the Si(111)-2×1 surface, Physical Review B, 84, (15), 2011, p155314- Journal Article, 2011 URL DOI TARA - Full Text

D. J. Arenas, L. V. Gasparov, Wei Qiu, J. C. Nino, C. H. Patterson and D. B. Tanner , Raman study of phonon modes in bismuth pyrochlores , Physical Review B, 82, (21), 2010, p214302-1 - 214302-8 Journal Article, 2010 TARA - Full Text URL DOI

Charles H. Patterson, First Principles Calculation of the Structure and Dielectric Properties of Bi2Ti2O7 , Physical Review B, 82, (15), 2010, p155103- Journal Article, 2010 TARA - Full Text URL DOI

Charles H. Patterson, Exciton: A Code for Excitations in Materials , Molecular Physics, 108, 2010, p1- Journal Article, 2010 URL DOI

A. D. Rowan, C. H. Patterson and L.V. Gasparov, Hybrid density functional theory applied to magnetite: Crystal structure, charge order, and phonons , Physical Review B, 79, 2009, p205103-1 - 205103-18 Journal Article, 2009 URL DOI TARA - Full Text

Charles H. Patterson, Small polarons and magnetic anti-phase boundaries in Ca2−xNaxCuO2Cl2 (x=0.06,0.12): origin of striped phases in cuprates, Physical Review B, 77, (9), 2008, p94523-1 - 94523-11 Journal Article, 2008 TARA - Full Text URL DOI

Charles H. Patterson, Electronic Structure and Lattice Vibrations of Ca2CuO2Cl2: a hybrid density functional study, Physical Review B, 77, (11), 2008, p115111-1 - 115111-6 Journal Article, 2008 URL TARA - Full Text DOI

Charles H. Patterson and S. Galamić-Mulaomerovi, Quasiparticle and Optical Excitations in Solid Ne and Ar: GW and BSE Approximations, AIP Conference Proceedings, International Conference on Computational Methods in Science and Engineering, Corfu, Greece, 25-30 September 2007, edited by Charles H. Patterson and S. Galamić-Mulaomerovi &George Maroulis, University of Patras , 963, (2B), American Institute of Physics, 2007, pp241-244 Conference Paper, 2007 URL DOI

Charles H. Patterson and S. Galamić‐Mulaomerović, Electronic Structure and Vibrational Spectra of Magnetite, AIP Conference Proceedings, International Conference on Computational Methods in Science and Engineering, Corfu, Greece, 25-30 September 2007, edited by George Maroulis, University of Patras Charles H. Patterson and Andrew D. Rowan Theodore E. Simos, University of Peloponnese George Maroulis, University of Patras , 963, (2B), American Institute of Physics, 2007, pp371-374 Conference Paper, 2007 DOI URL

S. Krishnamurthy, C. McGuinness, L. S. Dorneles, M. Venkatesan, J. M. D. Coey, J. G. Lunney, C. H. Patterson, K. E. Smith, T. Learmonth, P.A. Glans, T. Schmitt, J.-H. Guo, Soft x-ray spectroscopic investigation of ferromagnetic Co-doped ZnO, Journal of Applied Physics, 99, (08M111), 2006, p1 - 3 Journal Article, 2006 DOI TARA - Full Text

Charles H. Patterson, Comparison of hybrid density functional, Hartree-Fock, and GW calculations on NiO, International Journal of Quantum Chemistry, 106, (15), 2006, p3383 - 3386 Journal Article, 2006 URL DOI

Charles H. Patterson, Role of defects in ferromagnetism in Zn1-xCoxO: A hybrid density functional study, Physical Review B, 74, (14), 2006, p144432-1 - 144432-13 Journal Article, 2006 TARA - Full Text DOI

S. Galamic-Mulaomerovic and C.H. Patterson, Ab initio many-body calculation of excitons in solid Ne and Ar, Physical Review B, 72, 2005, p035127-1 - 035127-7 Journal Article, 2005 DOI

S. Galamic-Mulaomerovic and C.H. Patterson, Band structures of rare gas solids within the GW approximation, Physical Review B, 71, 2005, p195103-1 - 195103-8 Journal Article, 2005 DOI TARA - Full Text

Charles H. Patterson, Competing crystal structures in La0.5Ca0.5MnO3: conventional charge order versus Zener polarons, Physical Review B, 72, 2005, p085125-1 - 085125-5 Journal Article, 2005 DOI

Charles H. Patterson, Charge ordered oxygen ions and bi- and tri-Mn polarons in La0.5Ca0.5MnO3, Molecular Physics, 103, (18), 2005, p2507 - 2512 Journal Article, 2005 DOI

N.P. Konstantinidis and C.H. Patterson, Spin polaron effective magnetic model for La0.5Ca0.5MnO3, Physical Review B, 70, 2004, p064407-1 - 064407-8 Journal Article, 2004 DOI TARA - Full Text

C.H. Patterson and G. Zheng, Spin polaron electronic structure of La0.5Ca0.5MnO3: UHF and CI calculations, 272-276, 2004, pp124 - 126 Conference Paper, 2004 DOI

G. Zheng and C.H. Patterson, Ferromagnetic polarons in La0.5Ca0.5MnO3 and La0.33Ca0.67MnO3, Physical Review B, 67, 2003, p220404-1 - 220404-4 Journal Article, 2003 DOI TARA - Full Text

M. Nicastro and C.H. Patterson, Exchange coupling in CaMnO3 and LaMnO3: Configuration interaction and the coupling mechanism, Physical Review B, 65, 2002, p205111-1 - 205111-15 Journal Article, 2002 TARA - Full Text URL DOI

C.H. Patterson, Two approaches to teaching computational physics, Computing in Science and Engineering, 4, (6), 2002, p64 - 68 Journal Article, 2002 DOI

M. Nicastro, S. Galamic-Mulaomerovic and C.H. Patterson, Multipolar contributions to electron self-energies:extreme tight binding model, Journal of Physics: Condensed Matter, 13, 2001, p1215 - 1231 Journal Article, 2001 DOI

S. Galamic-Mulaomerovic, C.D. Hogan and C.H. Patterson, Eigenfunctions of the inverse dielectric function and response function of silicon and argon, 188, (4), 2001, pp1291 - 1296 Conference Paper, 2001 DOI

M. Nicastro, M. Kuzmin and C.H. Patterson, Spin and orbital ordering in CaMnO3 and LaMnO3: UHF calculations and the Goodenough model, Computational Materials Science, 17, 2000, p445 - 449 Journal Article, 2000 DOI

T. Somasundaram, R.M. Lynden-Bell RM, C.H. Patterson, The passage of gases through the liquid water vapour interface: a simulation study, Physical Chemistry Chemical Physics, 1, (1), 1999, p143 - 148 Journal Article, 1999

F. Renzoni, J. F. Donegan, C.H. Patterson, Optical gain and linewidth enhancement factor in bulk GaN, Semiconductor Science and Technology, 14, (6), 1999, p517 - 520 Journal Article, 1999 DOI

Patterson, C.H., Hogan, C.D., Nicastro, M. , Many-body theory applied to optical properties of silicon surfaces, Computer Physics Communications, Europhysics Conference on Computational Physics, Granada, Spain, September 2-5, 121, 1999, 711- Conference Paper, 1999 DOI

T. Somasundaram, M. in het Panhuis, R.M. Lynden-Bell, C.H. Patterson, A simulation study of the kinetics of passage of CO2 and N2 through the liquid/vapor interface of water, Journal of Chemical Physics, 111, (5), 1999, p2190 - 2199 Journal Article, 1999 TARA - Full Text DOI

M. in het Panhuis, C.H. Patterson, R.M. Lynden-Bell, A molecular dynamics study of carbon dioxide in water: diffusion, structure and thermodynamics, Molecular Physics, 94, (6), 1998, p963 - 972 Journal Article, 1998

C.D. Hogan, C.H. Patterson, Reflectance anisotropies of silicon surfaces: analysis of spectra in terms of surface excess susceptibilities, 404, (1-3), 1998, pp586 - 589 Conference Paper, 1998

C.D. Hogan, C.H. Patterson, Reflectance anisotropy of silicon surfaces: Discrete dipole calculation, Physical Review B, 57, (23), 1998, p14843 - 14849 Journal Article, 1998

D. Herrendorfer and C.H. Patterson, Dipole waves in semiconductors: The dielectric function and plasma oscillations of silicon, Journal of Physics and Chemistry of Solids, 58, (2), 1997, p207 - 220 Journal Article, 1997

C.H. Patterson and D. Herrendorfer, Reflectance anisotropy of the Si(100)1x2-As surface: Discrete dipole calculation, Journal of Vacuum Science and Technology A, 15, (6), 1997, p3036 - 3043 Journal Article, 1997

D. Herrendorfer, C.H. Patterson, Reflectivity and reflectance anisotropy of Si(100): A polarisable bond model, Surface Science, 375, (2-3), 1997, p210 - 220 Journal Article, 1997

J F McGilp, D Weaire and C H Patterson (eds), Epioptics - Linear and Nonlinear Optical Spectroscopy of Surfaces and Interfaces, Berlin, Springer-Verlag, 1995, 1 - 230pp Book, 1995

The linear optical response in, editor(s)J.F. McGilp, D. Weaire, C.H. Patterson , Epioptics: linear and nonlinear optical spectroscopy of surfaces and interfaces, Berlin, Springer, 1995, pp15 - 38, [R. del Sole, A. Shkrebtii, Guo-Ping J., C.H. Patterson] Book Chapter, 1995

C.H. Patterson, Bond polarisabilities at the C(111) 1x1-H surface and their application to 3 wave mixing experiments, Surface Science, 304, (3), 1994, p365 - 374 Journal Article, 1994

C.H. Patterson, A novel method for calculating bond-bond interactions of large systems, Chemical Physics Letters, 213, (1-2), 1993, p59 - 64 Journal Article, 1993

R.P. Messmer, C.H. Patterson, Long bonds in silicon clusters: a failure of conventional Moller-Plesset perturbation theory, Chemical Physics Letters, 192, (2-3), 1992, p277 - 282 Journal Article, 1992

J. D. O'Mahony, C. H. Patterson, J. F. McGilp, F. M. Leibsle, P. Weightman and, C. F. J. Flipse, The Au-induced 5 × 2 reconstruction on Si(111), Surface Science, 277, 1992, pL57 - L62 Journal Article, 1992 URL

C. H. Patterson, Bond calculation of optical second harmonic generation at gallium-terminated and arsenic-terminated Si(111) surfaces, Journal of Physics Condensed Matter, 4, 1992, p4017 - 4037 Journal Article, 1992

M.M. Lynam, L.V. Interrante, C.H. Patterson, R.P. Messmer, Comparison of isoelectronic aluminium nitrogen and silicon carbon double bonds using valence bond methods, Inorganic Chemistry, 30, (8), 1991, p1918 - 1922 Journal Article, 1991

C.H. Patterson, R.P. Messmer, Bonding and structures in silicon clusters: a valence bond interpretation, Physical Review B, 42, (12), 1990, p7530 - 7555 Journal Article, 1990

C.H. Patterson, R.P. Messmer, Valence bonds in the main group elements 2: the sulfur oxides, Journal of the American Chemical Society, 112, (11), 1990, p4138 - 4150 Journal Article, 1990

C.H. Patterson, J.M. Mundenar, P.Y. Timbrell, A.J. Gellman, R.M. Lambert, Molecular pathways in the cyclotrimerization of acetylene on Pd(111): vibrational spectra of the C4H4 intermediate and its thermal decomposition products, Surface Science, 208, (1-2), 1989, p93 - 112 Journal Article, 1989

C. H. Patterson and R. P. Messmer, The role of d functions in Sulfur Oxide molecules, Journal of the American Chemical Society, 111, 1989, p8059 - 8060 Journal Article, 1989 URL

C.H. Patterson, T.M. Buck, The binding site of CO on NiAl(110) determined by low energy ion scattering, Surface Science, 218, (2-3), 1989, p431 - 451 Journal Article, 1989

C. H. Patterson and R. P. Messmer, Structural compromise of the Arsenic terminated Si(111) surface, Physical Review B, 39, 1989, p1372 - 1374 Journal Article, 1989 URL

C.H. Patterson, R.M. Lambert, Molecular mechanisms in the cyclotrimerization of acetylene to benzene on palladium(111), Journal of Physical Chemistry, 92, (5), 1988, p1266 - 1270 Journal Article, 1988

I. Kamiya, T.M. Buck, T. Sakuri, C.H. Patterson, Preferential sputtering in dilute Cu-Ni alloys, Nuclear Instruments and Methods in Physics Research B Beam Interactions with Materials and Atoms, 33, (1-4), 1988, p479 - 481 Journal Article, 1988

C.H. Patterson, R.M. Lambert, Molecular pathways in the cyclotrimerization of ethyne on palladium - role of the C4 intermediate, Journal of the American Chemical Society, 110, (20), 1988, p6871 - 6877 Journal Article, 1988

C.H. Patterson, R.M. Lambert, Structure and Properties of the Palladium Sulfur Interface S2 Chemisorption on Pd(111), Surface Science, 187, (2-3), 1987, p339 - 358 Journal Article, 1987

P.A. Schultz, C.H. Patterson, R.P. Messmer, K-CO on Transition Metals: A Local Ionic Interaction, Journal of Vacuum Science and Technology A Vacuum Surfaces and Films, 5, (4 part 2), 1987, p1061 - 1064 Journal Article, 1987

Non-Peer-Reviewed Publications

C. H. Patterson, 'EXCITON code', TCD, 2017, - Software, 2017

C. H. Patterson, S. Banerjee, P. Kumar and J. F. McGilp, Au at the Si(111) surface: silicene and Au nanowires probed by optical spectroscopy, Collaborative Conference on 3D and Materials Research, Songdo Convensia, Incheon, S. Korea, 22nd June 2016, 2016 Oral Presentation, 2016

P. Kumar and C. H. Patterson, Optical characterisation of native point defects in ZnO and TiO2, European materials Research Society Spring Meeting, Lille, France, 11th - 15th May 2015, 2015 Poster, 2015

C. H. Patterson, The Irish Transition Year and TYPE, The Gangwon Education International Symposium 2014, Chuncheon, Gangwon, S. Korea, 28th November, 2014, Gangwon-do Provincial Office of Education Invited Talk, 2014

C. H. Patterson, Crystal structure, charge and orbital order in magnetite: a new perspective from DFT calculations, Group seminar, Korea Advanced Insitute for Science and Technology , 26th November, 2014 Oral Presentation, 2014

C. H. Patterson, Optical Spectroscopy of 1-D Nanostructures at Si(111) Surfaces, Group Seminar, Department of Physics, Yonsei University, Seoul, S. Korea, 25th November , 2014 Oral Presentation, 2014

C. H. Patterson, S. Banerjee, S. Jorgji, P. Kumar, J. F. McGilp, Optical Anisotropy Calculations on Semiconductor and Oxide Surfaces, 10th International Conference on Optics of Surfaces and Interfaces , Chemnitz, Germany, 8th - 13th September, 2013, Dietrich R. T. Zahn (Technische Universität Chemnitz) Friedhelm Bechstedt (Friedrich Schiller University Jena) Norbert Esser (Leibniz-Institut für Analytische Wissenschaften - ISAS e.V.) Invited Talk, 2013

C. H. Patterson and C. McNamee, Transition levels of defects in CuAlo2, DPG Spring Meeting, Regensburg, Germany, 10 - 15 March 2013, 2013 Oral Presentation, 2013 URL

C. H. Patterson, Dielectric properties of silicon surfaces, Group Seminar, S. N. Bose National Centre, Kolkata, India, February, 2013 Oral Presentation, 2013

C. H. Patterson, Dielectric properties of semiconductor surfaces, International workshop on computational materials design and engineering, IIT Jodhpur, India, February, 2013, Prof Ambesh Dixit, IIT Jodhpur Invited Talk, 2013

C. H. Patterson, S. Jorgji and J. F. McGilp, Reflectance anisotropy spectroscopyof clean and adsorbate covered Si(111) surfaces: comparison of experiment and hybrid DFT, DPG Spring Meeting, Regensburg, Germany, 10 - 15 March 2013, 2013 Oral Presentation, 2013 URL

C. H. Patterson, Magnetic defects promote ferromagnetism - do Zener polarons rule at 0K?, Seminar, Oak Ridge National Laboratory, TN, USA, May, 2006 Oral Presentation, 2006

C. H. Patterson, Many-body calculations for solids: progress and prospects, Quantum Theory Project Seminar, Department of Physics, University of Florida, October, 2005, Prof. Rodney Bartlett, University of Florida Invited Talk, 2005

C. H. Patterson, Electronic, magnetic and crystal structures of La0.5Ca0.5MnO3, EPSRC Metal Oxides Network Meeting, Rutherford Appleton Laboratory, UK, April, 2004, EPSRC Metal Oxides Network Invited Talk, 2004

C. H. Patterson, Ab initio studies of manganites: La0.5Ca0.5MnO3, Condensed Matter Theory Group Seminar, Department of Physics, University of Bristol, July, 2003, Prof James Annett Invited Talk, 2003

C. H. Patterson, Ab initio many-body calculations for solids: Ne and Ar, Theoretical Chemistry Group Seminar, Department of Chemistry, University of Turin, April , 2003 Oral Presentation, 2003

Charles H. Patterson, Donal MacKernan, 7th Irish Atomistic Simulators' Meeting, 2002, Trinity College Dublin Meetings /Conferences Organised, 2002

C. H. Patterson, The computational physics degree at Trinity College Dublin, American Physical Society Division of Computational Physics Annual Meeting, Massachussetts Institute of Technology , July, 2001, American Physical Society Division of Computational Physics Invited Talk, 2001

Charles H. Patterson, 4th Irish Atomistic Simulators' Meeting, 1999, Trinity College Dublin Meetings /Conferences Organised, 1999

C. H. Patterson, Discrete dipole calculations of surface optical properties, International school of solid state physics: EPIOPTICS 4, Erice, Sicily, June, 1996 Invited Talk, 1996

Charles H. Patterson, R.M. Lynden-Bell, 1st Irish Atomistic Simulators' Meeting, 1996, Trinity College Dublin Meetings /Conferences Organised, 1996

E. Mehes and C. H. Patterson, Defect levels and optical spectra of the Si(001):a-SiO2 interface, Workshop on dielectrics in microelectronics, Kinsale, Co. Cork, Ireland, 9th - 11th June 2014 Poster,

Research Expertise

Description

Electronic structure theory code development Optics of semiconductor surfaces and interfaces Computational materials science Many-body theory of electrons in solids Electronic structure of magnetic materials My research consists of developing and applying electronic structure methods to problems in molecular, condensed matter and materials physics. Electronic structure theory is now a relatively mature field and density functional theory codes are available for many applications. More accurate many body methods, based on electron Green's functions, and electron-hole polarization propagators yield the most accurate predictions of excited state properties (Excitons) of molecules and condensed matter. The Exciton code performs self-consistent field Hartree-Fock calculations as well as GW (Green's function) and Bethe-Salpeter Equation calculations. Electronic structure codes divide roughly into those which represent electron wave functions using plane waves and those which use local orbitals. The former are best suited to crystalline materials with limited numbers of atoms per unit cell, the latter have many advantages for molecules, especially large molecules and systems with little or no symmetry. Accurate electronic structure methods such as the GW Green's function method and Bethe-Salpeter Equation polarization propagator method have applications in optical excitations of biomolecules, photovoltaics and photocatalysts for light harvesting and chemical reaction promotion such as artificial photosynthesis. Development of the Exciton code was begun with two graduate students, Drs. Conor Hogan and Svjetlana Galamic-Mulaomerovic, over a decade ago. That first phase of code development was based on a plane wave representation of the Coulomb potential, which is straightforward to code. The original Exciton code resulted in two publications in Physical Review B in 2005. Based on experience gained in developing the first Exciton code, I began developing an entirely new version of the code during a sabbatical year spent at the Quantum Theory Project, University of Florida, hosted by Prof. Rodney Bartlett. The new code employs the Ewald representation of the Coulomb potential for periodic systems. It makes full use of point, layer or space group symmetries in real and reciprocal space as well as time-reversal symmetry in reciprocal space. Symmetry is also used to transform the Gaussian atomic orbital basis into a symmetry adapted basis, which results in block diagonalization of operators, a reduction of running time and increased accuracy of wave functions. The many-body part of the code relies on an approach called Density fitting, which greatly reduces the time required to calculate Coulomb integrals over molecular orbitals. Current applications of the self-consistent Hartree-Fock, GW and BSE modules in the code to moleclues and molecular complexes have been tested using up to 1800 basis functions in the wave function basis and 4500 basis functions in the density fitting basis. Future development of the code will include the capacity to perform GW and Bethe-Salpeter Equation calculations for crystalline systems. Applications where the code would have significant advantages over plane wave codes are metal organic framework (MOF) materials which have open structures. Exciton is developed in C++ and MPI and consists of around 50,000 lines of code. The current Exciton code is also interfaced to the Crystal code which allows it to perform single-particle optical excitations calculations using wave functions and energy band structures from Crystal. This part of Exciton led to 15 publications in the seven year period since 2010. This version of the code produced two publications in 2005.

Projects

  • Title
    • Exciton Computer Code
  • Summary
    • My research consists of developing and applying electronic structure methods to problems in molecular, condensed matter and materials physics. Electronic structure theory is now a relatively mature field and density functional theory codes are available for many applications. More accurate many body methods, based on electron Green's functions, and electron-hole polarization propagators yield the most accurate predictions of excited state properties (Excitons) of molecules and condensed matter. The Exciton code performs self-consistent field Hartree-Fock calculations as well as GW (Green's function) and Bethe-Salpeter Equation calculations. Electronic structure codes divide roughly into those which represent electron wave functions using plane waves and those which use local orbitals. The former are best suited to crystalline materials with limited numbers of atoms per unit cell, the latter have many advantages for molecules, especially large molecules and systems with little or no symmetry. Accurate electronic structure methods such as the GW Green's function method and Bethe-Salpeter Equation polarization propagator method have applications in optical excitations of biomolecules, photovoltaics and photocatalysts for light harvesting and chemical reaction promotion such as artificial photosynthesis. Development of the Exciton code was begun with two graduate students, Drs. Conor Hogan and Svjetlana Galamic-Mulaomerovic, over a decade ago. That first phase of code development was based on a plane wave representation of the Coulomb potential, which is straightforward to code. The original Exciton code resulted in two publications in Physical Review B in 2005. Based on experience gained in developing the first Exciton code, I began developing an entirely new version of the code during a sabbatical year spent at the Quantum Theory Project, University of Florida, hosted by Prof. Rodney Bartlett. The new code employs the Ewald representation of the Coulomb potential for periodic systems. It makes full use of point, layer or space group symmetries in real and reciprocal space as well as time-reversal symmetry in reciprocal space. Symmetry is also used to transform the Gaussian atomic orbital basis into a symmetry adapted basis, which results in block diagonalization of operators, a reduction of running time and increased accuracy of wave functions. The many-body part of the code relies on an approach called Density fitting, which greatly reduces the time required to calculate Coulomb integrals over molecular orbitals. Current applications of the self-consistent Hartree-Fock, GW and BSE modules in the code to moleclues and molecular complexes have been tested using up to 1800 basis functions in the wave function basis and 4500 basis functions in the density fitting basis. Future development of the code will include the capacity to perform GW and Bethe-Salpeter Equation calculations for crystalline systems. Applications where the code would have significant advantages over plane wave codes are metal organic framework (MOF) materials which have open structures. Exciton is developed in C++ and MPI and consists of around 50,000 lines of code. The current Exciton code is also interfaced to the Crystal code which allows it to perform single-particle optical excitations calculations using wave functions and energy band structures from Crystal. This part of Exciton led to 15 publications in the seven year period since 2010. This version of the code produced two publications in 2005.
  • Funding Agency
    • Higher Education Authority/Enterprise Ireland
  • Date From
    • January 2000
  • Date To
    • Current
  • Title
    • Surface and Interface Optics Calculations
  • Summary
    • Light can be used as a probe of the electronic properties of matter in situations where conventional light-in/charged particle-out spectroscopies such as photoelectron spectroscopies cannot. The ejected electron in photoelectron spectroscopy cannot be detected if the ambient surrounding the sample is not high vacuum. In contrast, light-in/light-out spectroscopies such as reflectance measurements can be used without a vacuum ambient. The surface and interface optics project is focussed on applying density functional theory (DFT) methods to calculation of optical spectra of surfaces and interfaces of semiconductors and oxides. The work is done in collaboration with experimentalists, notably Prof. John McGilp in the School of Physics. Recent work on the interface between GaP thin films and the underlying Si substrate has been done with Prof. T. Hannappel and Dr. O. Supplie at the Helmholtz-Zentrum, Berlin who are experimentalists working on this prototype system for III-V semiconductor growth on silicon. Reflection of light by a surface depends on the dielectric responses of atoms from the surface layer to many layers below the surface. In order to use visible light as a probe of electrons at surfaces, it is essential to distinguish the reflected signal coming from the layers immediately at the surface from that coming from many more layers near the surface. One way of doing this is to choose systems where the surface is anisotropic in the surface plane while the underlying layers are isotropic. An example of an isotropic surface is where surface atoms form pairs (or dimerize) in chains at (001) surfaces of silicon or III-V semiconductors. If the difference in reflectivity of light is measured in normal incidence with the optical polarization vector aligned parallel or perpendicular to the dimer chains, then the surface contribution to reflectivity arises only from the anisotropic surface. Reflectance anisotropy spectroscopy (RAS) consists of measuring this difference, usually in the photon energy range from 1 to 5 eV. The experimental measurement by itself yields only a fingerprint of the surface. In order to use RAS to obtain information about electronic properties of the surface, experimental data must be compared to results of our calculations using the Crystal and Exciton codes. These calculations show which features in a RAS spectrum arise from transitions between particular surface states. Armed with this analysis, experimentalists may use the RAS technique to diagnose the electronic properties of a surface on which a semiconductor is being grown under non-high vacuum conditions. One recent highlight of this work has been application of the methods that we have developed since 2010 for calculating RAS for surfaces, to the interface between GaP thin films grown on the Si(001) surface by Hannappel and Supplie in Berlin. They measured the dielectric anisotropy of the interface between the thin film and silicon substrate. My PhD student, Pankaj Kumar, calculated the dielectric anisotropy for this interface using Crystal and Exciton and found agreement between theory and experiment only when the silicon substrate was doped so that the interface was semiconducting. Our work showed that the measured interface dielectric anisotropy arises from electrons trapped in interface states localized in several layers of silicon atoms closest to the first P layer in the GaP thin film. It also showed that if the GaP layer was terminated by a Ga/Si interface, the interface dielectric anisotropy spectrum was quite different. Thus a combination of theory and experiment can show whether a buried interface is conducting or semiconducting and whether the GaP layer in contact with the Si substrate is Ga or P. Our work is, as far as we can tell, the first application of DFT to the optical anisotropy of an interface and it has been accepted for publication in Physical Review Letters.
  • Funding Agency
    • Science Foundation Ireland
  • Date From
    • October 2009
  • Date To
    • September 2014
  • Title
    • Charge and Orbital Order in Magnetite
  • Summary
    • Many of the most exotic states and properties of matter such as superconductivity, charge and spin order, etc arise in materials with unpaired electron spins on metal ions such as Fe3+ or Cu2+. My work in this area includes first principles hybrid density functional theory (DFT) calculations on manganites, cuprates and magnetite. Magnetite is a ferrimagnet, also known as lodestone, which has an unusual phase transition between a conducting and semiconducting state at 120 K, known as the Verwey transition. The contribution that I and my student, Andrew Rowan, and Prof. Lev Gasparov at the University of North Florida made in this area is in understanding charge order in the above mentioned materials. My most recent work in this area has been on elucidating the charge order in magnetite in the semiconducting phase of magnetite which exists below the Verwey temperature. The transition has puzzled physicists, including many distinguished scientists, since its discovery by Verwey in 1939. The problem is quite simple to explain. Magnetite consists of Fe3+ ions in tetrahedral 'A' sites and an equal proportion of Fe2+ and Fe3+ ions in octahedral 'B' sites. Fe2+ and Fe3+ ions are in d6 and d5 electronic configurations, respectively. This means that half of the ions at 'B' sites contain one minority spin electron, which is responsible for conduction above the Verwey transition temperature and must somehow become immobile below the Verwey temperature. It is this question that has puzzled physicists for 75 years. A complicating factor in determining the cause of the Verwey transition was that the structure of magnetite in the low temperature phase was poorly resolved because if multiple twinning of domains. It was finally resolved by Attfield and coworkers who used x-ray diffraction on a micron sized grain with one dominant domain in 2012 [Nature 481, 173 (2012)]. The unit cell contains 112 ions and has 16 types of Fe 'B' site and 8 types of 'A' site. The low temperature phase shows charge ordering of electrons on Fe 'B' sites, which is associated with the change in electric conductivity and which was dubbed 'trimeron' formation by Attfield and coworkers. Some chains of 3 Fe ions showed on of the conduction electrons being localized on 3 Fe ions. My contribution to this problem was to calculate the NMR (nuclear magnetic resonance) spectra of 'A' and 'B' site Fe ions in the newly discovered structure of magnetite as a function of crystal orientation in an external magnetic field. NMR is a potentially powerful probe of charge order in Fe compounds because 57Fe is a spin " nucleus which will couple to the minority spin electron in d6 Fe2+. Measurement of the NMR resonance frequency as a function of orientation of the magnetite crystal in a magnetic field yields curves which are characteristic of the shape of the d orbital containing this electron. My paper published in Physical Review B in 2014 showed that hybrid DFT calculations using the Crystal code and the crystal structure published by Attfield and coworkers in 2012 could reproduce the variation of NMR frequency with crystal orientation, and therefore that the charge order in our calculations was correct. I concluded that molecular polarons and charge localization in zig-zag chains (Attfield's trimerons) was responsible for the Verwey transition. Hybrid DFT calculation of 57Fe NMR resonances and orbital order in magnetite , C. H. Patterson, Phys. Rev. B 90, 075134 (2014) Hybrid Density Functional Theory Applied to Magnetite: Crystal Structure, Charge Order and Phonons, A. D. Rowan, C. H. Patterson and L. V. Gasparov, Phys. Rev. B 79 205103 (2009)
  • Funding Agency
    • Science Foundation Ireland

Keywords

Atomic and molecular physics; Computational Physics; Condensed matter, electronic, magnetic and superconductive properties; Condensed matter, optical and dielectric properties; Magnetism and spin electronics; Quantum chemistry; Quantum mechanics; Theory and computational physics

Recognition

Representations

Board or Steering Group Member, Psi-k Network www.Psi-k.org. European Network funded by successive European Commission Human Capital and Mobility and two 5 year European Science Foundation grants. 1994 to 2016

Board Member, European Physical Society Computational Physics Group. 1997 to 2002

Awards and Honours

Fellow of TCD 2000

Memberships

American Physical Society

Institute of Physics