RC ANDREW - Academia.edu (original) (raw)
Papers by RC ANDREW
![Research paper thumbnail of Erratum: Mechanical properties of graphene and boronitrene [Phys. Rev. B 85 , 125428 (2012)]](https://attachments.academia-assets.com/73289496/thumbnails/1.jpg)
](Physical Review B
Equation (10) for the two-dimensional bulk modulus γ of a general anisotropic medium should be re... more Equation (10) for the two-dimensional bulk modulus γ of a general anisotropic medium should be replaced by [1] γ = c 11 c 22 − c 2 12 (c 11 + c 22 − 2c 12). Equation (10) was not used in our paper since all materials described were isotropic and since this expression is correct in the special case of isotropy. Thus, no results have been affected by this finding. We acknowledge Prof. D. Tomanek and Prof. A. Every for pointing out the error.
European Journal of Physics
A key concept in material science is the relationship between the Bravais lattice, the reciprocal... more A key concept in material science is the relationship between the Bravais lattice, the reciprocal lattice and the resulting Brillouin zones (BZ). These zones are often complicated shapes that are hard to construct and visualise without the use of sophisticated software, even by professional scientists. We have used a simple sorting algorithm to construct BZ of any order for a chosen Bravais lattice that is easy to implement in any scientific programming language. The resulting zones can then be visualised using freely available plotting software. This method has pedagogical value for upper-level undergraduate students since, along with other computational methods, it can be used to illustrate how constant-energy surfaces combine with these zones to create van Hove singularities in the density of states. In this paper we apply our algorithm along with the empirical pseudopotential method and the 2D equivalent of the tetrahedron method to show how they can be used in a simple software project to investigate this interaction for a 2D crystal. This project not only enhances students' fundamental understanding of the principles involved but also improves transferable coding skills.
Journal of Electronic Materials, 2016
In this work, the results of density functional theory calculations for rare earth (Ce, Pr, Eu an... more In this work, the results of density functional theory calculations for rare earth (Ce, Pr, Eu and Er) interstitials in Ge are presented. We employed the hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE06) for all the calculations. We calculated the formation energies and charge state transition levels for the tetrahedral (T) and hexagonal (H) configurations of the Ce, Pr, Eu and Er interstitials in Ge. While for the T configuration, the charge states of the Ce and Pr did not induce any thermodynamic accessible transition state level within the band gap of Ge, for both the T and H configurations the Eu and Er interstitials in Ge induce deep levels in the band gap. The H configuration of the Ce interstitial
Journal of Physics: Condensed Matter, 2016
We perform ab-initio density functional theory calculations to investigate the energetics, electr... more We perform ab-initio density functional theory calculations to investigate the energetics, electronic and magnetic properties of isolated stoichiometric and non-stoichiometric substitutional Si complexes in a hexagonal boron-nitride monolayer. The Si impurity atoms substituting the boron atom sites Si B giving non-stoichiometric complexes are found to be the most energetically favourable, and are half-metallic and order ferromagnetically in the neutral charge state. We find that the magnetic moments and magnetization energies increase monotonically when Si defects form a cluster. Partial density of states and standard Mulliken population analysis indicate that the half-metallic character and magnetic moments mainly arise from the Si 3p impurity states. The stoichiometric Si complexes are energetically unfavorable and non-magnetic. When charging the energetically favourable non-stoichiometric Si complexes, we find that the formation energies strongly depend on the impurity charge states and Fermi level position. We also find that the magnetic moments and orderings are tunable by charge state modulation q =-2,-1, 0, +1, +2. The induced half-metallic character is lost (retained) when charging isolated (clustered) Si defect(s). This underlines the potential of a Si doped hexagonal boron-nitride monolayer for novel spin-based applications.
Journal of Physics A: Mathematical and Theoretical, 2008
ABSTRACT The genesis of spurious solutions in finite basis approximations to operators which poss... more ABSTRACT The genesis of spurious solutions in finite basis approximations to operators which possess a continuum and a point spectrum is discussed and a simple solution for identifying these solutions is suggested. The article commented on was published in J. Phys. A, Math. Gen. 38, No. 14, 3157–3171 (2005; Zbl 1065.81036).
Journal of Medicinal Chemistry, 1994
The substrate specificity at the active site of recombinant human synovial fluid phospholipase Az... more The substrate specificity at the active site of recombinant human synovial fluid phospholipase Az (hs-PLA2) was investigated by the preparation of a series of short-chain phospholipid analogs and measurement of their enzymatic hydrolysis at concentrations well below the critical micelle concentration. Substrates used in the study included 1,2-dihexanoylglycerophospholipids, 1,2bis(alkanoylthio)glycerophospholipids, and l-O-alkyl-2-(alkanoylthio)phospholipids. Turnover was observed for only a few of the 1,2-dihexanoylglycerophospholipids, and the rate of hydrolysis was very low, near the limit of detection of the assay. In contrast, selected 24alkanoylthio)glycerophospholipids were hydrolyzed by hs-PLAz a t much higher rates a t concentrations well below their critical micelle concentration (cmc). Thus, the 1,2-bis(hexanoylthio)glycerophosphatidylmethanol exhibits a kCatlKLI = 1800 L mol-' s-l. Over the calculated log P (cLogP) range of 3-9, cLogP and log(k,,,lK~, were linearly related for compounds with straight-chain sn-1 and sn-2 substituents. At comparable cLogP's, the sn-1 ethers and thioesters were hydrolyzed at comparable rates. A negative charge in the phosphate head group was required for enzyme activity. Unsaturation, aromaticity, and branching in the sn-2 substituent reduce turnover dramatically. The same structural modifications in the sn-1 substituent have less effect on turnover. Certain of these substrates, e.g., 1,2-bis(hexanoylthio)glycerophosphatidylmethanol, may be useful in assaying for active site inhibitors of PLAr. The structureactivity relationships established here for substrates should serve as a reference for the structure-activity relationships of substrate-based inhibitors. * Authors to whom inquiries should be directed. ' Division of Medicinal Chemistry.
The Journal of Chemical Physics, 2013
Using first principles methods, we study the mechanical properties of monolayer and bilayer graph... more Using first principles methods, we study the mechanical properties of monolayer and bilayer graphene with 50% and 100% coverage of hydrogen. We employ the vdW-DF, vdW-DF-C09 x and vdW-DF2-C09 x van der Waals functionals for the exchange correlation interactions that give significantly improved interlayer spacings and energies. We also use the PBE form for the generalized gradient corrected exchange correlation functional for comparison. We present a consistent theoretical framework for the in-plane layer modulus and the out-of-plane interlayer modulus and we calculate, for the first time, these properties for these systems. This gives a measure of the change of the strength properties when monolayer and bilayer graphene are hydrogenated. As well as comparing the relative performance of these functionals in describing hydrogenated bilayered graphenes, we also benchmark these functionals in how they calculate the properties of graphite.
Chemical Physics Letters, 2009
ABSTRACT Covergent eigensolutions of the Dirac Equation for a relativistic electron in an externa... more ABSTRACT Covergent eigensolutions of the Dirac Equation for a relativistic electron in an external Coulomb potential are obtained using the Lanczos Algorithm. A tri-diagonal matrix representation of the Dirac Hamiltonian operator is constructed iteratively and diagonalized after each iteration step to form a sequence of convergent eigenvalue solutions. Any spurious solutions which arise from the presence of continuum states can easily be identified.
Physical Review B
Equation (10) for the two-dimensional bulk modulus γ of a general anisotropic medium should be re... more Equation (10) for the two-dimensional bulk modulus γ of a general anisotropic medium should be replaced by [1] γ = c 11 c 22 − c 2 12 (c 11 + c 22 − 2c 12). Equation (10) was not used in our paper since all materials described were isotropic and since this expression is correct in the special case of isotropy. Thus, no results have been affected by this finding. We acknowledge Prof. D. Tomanek and Prof. A. Every for pointing out the error.
European Journal of Physics
A key concept in material science is the relationship between the Bravais lattice, the reciprocal... more A key concept in material science is the relationship between the Bravais lattice, the reciprocal lattice and the resulting Brillouin zones (BZ). These zones are often complicated shapes that are hard to construct and visualise without the use of sophisticated software, even by professional scientists. We have used a simple sorting algorithm to construct BZ of any order for a chosen Bravais lattice that is easy to implement in any scientific programming language. The resulting zones can then be visualised using freely available plotting software. This method has pedagogical value for upper-level undergraduate students since, along with other computational methods, it can be used to illustrate how constant-energy surfaces combine with these zones to create van Hove singularities in the density of states. In this paper we apply our algorithm along with the empirical pseudopotential method and the 2D equivalent of the tetrahedron method to show how they can be used in a simple software project to investigate this interaction for a 2D crystal. This project not only enhances students' fundamental understanding of the principles involved but also improves transferable coding skills.
Journal of Electronic Materials, 2016
In this work, the results of density functional theory calculations for rare earth (Ce, Pr, Eu an... more In this work, the results of density functional theory calculations for rare earth (Ce, Pr, Eu and Er) interstitials in Ge are presented. We employed the hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE06) for all the calculations. We calculated the formation energies and charge state transition levels for the tetrahedral (T) and hexagonal (H) configurations of the Ce, Pr, Eu and Er interstitials in Ge. While for the T configuration, the charge states of the Ce and Pr did not induce any thermodynamic accessible transition state level within the band gap of Ge, for both the T and H configurations the Eu and Er interstitials in Ge induce deep levels in the band gap. The H configuration of the Ce interstitial
Journal of Physics: Condensed Matter, 2016
We perform ab-initio density functional theory calculations to investigate the energetics, electr... more We perform ab-initio density functional theory calculations to investigate the energetics, electronic and magnetic properties of isolated stoichiometric and non-stoichiometric substitutional Si complexes in a hexagonal boron-nitride monolayer. The Si impurity atoms substituting the boron atom sites Si B giving non-stoichiometric complexes are found to be the most energetically favourable, and are half-metallic and order ferromagnetically in the neutral charge state. We find that the magnetic moments and magnetization energies increase monotonically when Si defects form a cluster. Partial density of states and standard Mulliken population analysis indicate that the half-metallic character and magnetic moments mainly arise from the Si 3p impurity states. The stoichiometric Si complexes are energetically unfavorable and non-magnetic. When charging the energetically favourable non-stoichiometric Si complexes, we find that the formation energies strongly depend on the impurity charge states and Fermi level position. We also find that the magnetic moments and orderings are tunable by charge state modulation q =-2,-1, 0, +1, +2. The induced half-metallic character is lost (retained) when charging isolated (clustered) Si defect(s). This underlines the potential of a Si doped hexagonal boron-nitride monolayer for novel spin-based applications.
Journal of Physics A: Mathematical and Theoretical, 2008
ABSTRACT The genesis of spurious solutions in finite basis approximations to operators which poss... more ABSTRACT The genesis of spurious solutions in finite basis approximations to operators which possess a continuum and a point spectrum is discussed and a simple solution for identifying these solutions is suggested. The article commented on was published in J. Phys. A, Math. Gen. 38, No. 14, 3157–3171 (2005; Zbl 1065.81036).
Journal of Medicinal Chemistry, 1994
The substrate specificity at the active site of recombinant human synovial fluid phospholipase Az... more The substrate specificity at the active site of recombinant human synovial fluid phospholipase Az (hs-PLA2) was investigated by the preparation of a series of short-chain phospholipid analogs and measurement of their enzymatic hydrolysis at concentrations well below the critical micelle concentration. Substrates used in the study included 1,2-dihexanoylglycerophospholipids, 1,2bis(alkanoylthio)glycerophospholipids, and l-O-alkyl-2-(alkanoylthio)phospholipids. Turnover was observed for only a few of the 1,2-dihexanoylglycerophospholipids, and the rate of hydrolysis was very low, near the limit of detection of the assay. In contrast, selected 24alkanoylthio)glycerophospholipids were hydrolyzed by hs-PLAz a t much higher rates a t concentrations well below their critical micelle concentration (cmc). Thus, the 1,2-bis(hexanoylthio)glycerophosphatidylmethanol exhibits a kCatlKLI = 1800 L mol-' s-l. Over the calculated log P (cLogP) range of 3-9, cLogP and log(k,,,lK~, were linearly related for compounds with straight-chain sn-1 and sn-2 substituents. At comparable cLogP's, the sn-1 ethers and thioesters were hydrolyzed at comparable rates. A negative charge in the phosphate head group was required for enzyme activity. Unsaturation, aromaticity, and branching in the sn-2 substituent reduce turnover dramatically. The same structural modifications in the sn-1 substituent have less effect on turnover. Certain of these substrates, e.g., 1,2-bis(hexanoylthio)glycerophosphatidylmethanol, may be useful in assaying for active site inhibitors of PLAr. The structureactivity relationships established here for substrates should serve as a reference for the structure-activity relationships of substrate-based inhibitors. * Authors to whom inquiries should be directed. ' Division of Medicinal Chemistry.
The Journal of Chemical Physics, 2013
Using first principles methods, we study the mechanical properties of monolayer and bilayer graph... more Using first principles methods, we study the mechanical properties of monolayer and bilayer graphene with 50% and 100% coverage of hydrogen. We employ the vdW-DF, vdW-DF-C09 x and vdW-DF2-C09 x van der Waals functionals for the exchange correlation interactions that give significantly improved interlayer spacings and energies. We also use the PBE form for the generalized gradient corrected exchange correlation functional for comparison. We present a consistent theoretical framework for the in-plane layer modulus and the out-of-plane interlayer modulus and we calculate, for the first time, these properties for these systems. This gives a measure of the change of the strength properties when monolayer and bilayer graphene are hydrogenated. As well as comparing the relative performance of these functionals in describing hydrogenated bilayered graphenes, we also benchmark these functionals in how they calculate the properties of graphite.
Chemical Physics Letters, 2009
ABSTRACT Covergent eigensolutions of the Dirac Equation for a relativistic electron in an externa... more ABSTRACT Covergent eigensolutions of the Dirac Equation for a relativistic electron in an external Coulomb potential are obtained using the Lanczos Algorithm. A tri-diagonal matrix representation of the Dirac Hamiltonian operator is constructed iteratively and diagonalized after each iteration step to form a sequence of convergent eigenvalue solutions. Any spurious solutions which arise from the presence of continuum states can easily be identified.