@article{bungaro_rapcewicz_bernholc_2000, title={Ab initio phonon dispersions of wurtzite AlN, GaN, and InN}, volume={61}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.61.6720}, abstractNote={Phonon excitations play an important role in electronic transport, nonradiative electron-relaxation processes, and other properties of interest for materials characterization, device engineering, and design. We have calculated the phonon dispersions and density of states for wurtzite AlN, GaN, and InN using state-of-the-art density-functional perturbation theory. The calculations are in good agreement with the existing experimental data for zone-center modes and predict the full phonon dispersions throughout the Brillouin zone. In particular, it is found that the three-phonon decay of the LO phonon in two acoustic phonons is not allowed in GaN and InN, since the LO frequency is much larger than the acoustic frequencies over the entire spectrum.}, number={10}, journal={PHYSICAL REVIEW B}, author={Bungaro, C and Rapcewicz, K and Bernholc, J}, year={2000}, month={Mar}, pages={6720–6725} }
 @article{bernholc_briggs_bungaro_nardelli_fattebert_rapcewicz_roland_schmidt_zhao_2000, title={Large-scale applications of real-space multigrid methods to surfaces, nanotubes, and quantum transport}, volume={217}, ISSN={["1521-3951"]}, DOI={10.1002/(sici)1521-3951(200001)217:1<685::aid-pssb685>3.0.co;2-3}, abstractNote={The development and applications of real-space multigrid methods are discussed. Multigrid techniques provide preconditioning and convergence acceleration at all length scales, and therefore lead to particularly efficient algorithms. When using localization regions and optimized, non-orthogonal orbitals, calculations involving over 1000 atoms become practical on massively parallel computers. The applications discussed in this chapter include: (i) dopant incorporation and ordering effects during surface incorporation of boron, which lead to the formation of ordered domains at half-monolayer coverage; (ii) incorporation of Mg into GaN during growth, and in particular the conditions that would lead to maximum p-type doping; (iii) optical fingerprints of surface structures for use in real-time feedback control of growth; and (iv) mechanisms of stress release and quantum transport properties of carbon nanotubes.}, number={1}, journal={PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS}, author={Bernholc, J and Briggs, EL and Bungaro, C and Nardelli, MB and Fattebert, JL and Rapcewicz, K and Roland, C and Schmidt, WG and Zhao, Q}, year={2000}, month={Jan}, pages={685–701} }
 @article{boguslawski_rapcewicz_bernholc_2000, title={Surface segregation and interface stability of AlN/GaN, GaN/InN, and AlN/InN {0001} epitaxial systems}, volume={61}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.61.10820}, abstractNote={Surface segregation in wide band-gap nitride alloys was studied using ab initio calculations. In agreement with recent experiments we find that ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ {0001} surfaces prefer Ga termination, and ${\mathrm{Ga}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{N}$ and ${\mathrm{Al}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{N}$ {0001} prefer In termination. The segregation energy is found to depend critically on the type of surface reconstruction. For cation-terminated reconstructions on both the (0001) and $(0001\ifmmode\bar\else\textasciimacron\fi{})$ surfaces the segregation energies are similar and an order of magnitude larger than in the arsenides or Si/Ge systems. The largest segregation energy of about 3.6 eV is found for the AlN/InN surface. In contrast, segregation effects for the N-adatom $2\ifmmode\times\else\texttimes\fi{}2$ reconstruction on the (0001) surfaces are strongly suppressed. At AlN/GaN and GaN/InN interfaces the segregation effects are very weak and should not affect their morphology. Our results suggest the choice of optimal conditions of growth that lead to sharp interfaces and longer lifetimes of carriers in III-nitride heterosystems.}, number={16}, journal={PHYSICAL REVIEW B}, author={Boguslawski, P and Rapcewicz, K and Bernholc, JJ}, year={2000}, month={Apr}, pages={10820–10826} }
 @article{bungaro_rapcewicz_bernholc_1999, title={Surface sensitivity of impurity incorporation: Mg at GaN (0001) surfaces}, volume={59}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.59.9771}, abstractNote={The interplay of surface termination, reconstruction patterns, and availability of species involved determines the incorporation of impurities during growth. We study ab initio this interplay for Mg at the GaN (0001) surfaces and find that optimal incorporation conditions strongly depend upon surface orientation and cannot be predicted using bulk stoichiometric arguments. With reasonable assumptions on the kinetics, high densities of Mg can be achieved in the absence of hydrogen and the Ga surface displays superior incorporation characteristics to that of the N surface.}, number={15}, journal={PHYSICAL REVIEW B}, author={Bungaro, C and Rapcewicz, K and Bernholc, J}, year={1999}, month={Apr}, pages={9771–9774} }
 @article{rapcewicz_chen_yakobson_bernholc_1998, title={Consistent methodology for calculating surface and interface energies}, volume={57}, ISSN={["1550-235X"]}, DOI={10.1103/physrevb.57.7281}, abstractNote={A consistent approach to the calculation of the surface energy valid for all crystal systems is presented. Voronoi polyhedra are introduced and used in conjunction with the energy-density formalism of Chetty and Martin [Phys. Rev. B 45, 6074 (1992); 45, 6089 (1992)] to provide a methodology for the determination of surface energies. The surface energies of the unrelaxed, unreconstructed GaAs (001) and (111) surfaces are calculated as a test. As an example of the application of the formalism to a low symmetry system, the energies of selected (0001) surfaces of the wide-gap semiconductors GaN and SiC are determined.}, number={12}, journal={PHYSICAL REVIEW B}, author={Rapcewicz, K and Chen, B and Yakobson, B and Bernholc, J}, year={1998}, month={Mar}, pages={7281–7291} }
 @article{nardelli_rapcewicz_bernholc_1997, title={Polarization field effects on the electron-hole recombination dynamics in In0.2Ga0.8N/In1-xGaxN multiple quantum wells}, volume={71}, DOI={10.1063/1.120269}, abstractNote={The effect of the polarization field in wurtzite In0.2Ga0.8N/In1−xGaxN (x>0.8) multiple quantum wells is studied from first principles. The pyroelectric and piezoelectric fields naturally present in the system due to its wurtzite structure are strong enough to reduce the interband recombination rate in an ideal quantum well. We suggest that composition fluctuations, observed in the active region of actual devices, provide the necessary confinement for an improved recombination rate and lasing.}, number={21}, journal={Applied Physics Letters}, author={Nardelli, M. B. and Rapcewicz, K. and Bernholc, Jerzy}, year={1997}, pages={3135–3137} }
 @article{bernholc_briggs_sullivan_brabec_nardelli_rapcewicz_roland_wensell_1997, title={Real space multigrid methods for large scale electronic structure problems}, volume={65}, DOI={10.1002/(SICI)1097-461X(1997)65:5<531::AID-QUA18>3.0.CO;2-5}, abstractNote={We describe the development and applications of a new electronic structure method that uses a real-space grid as a basis. Multigrid techniques provide preconditioning and convergence acceleration at all length scales and therefore lead to particularly efficient algorithms. The salient points of our implementation include: (i) new compact discretization schemes in real space for systems with cubic, orthorhombic, and hexagonal symmetry and (ii) new multilevel algorithms for the iterative solution of Kohn–Sham and Poisson equations. The accuracy of the discretizations was tested by direct comparison with plane-wave calculations, when possible, and the results were in excellent agreement in all cases. These techniques are very suitable for use on massively parallel computers and in O(N) methods. Tests on the Cray-T3D have shown nearly linear scaling of the execution time up to the maximum number of processors (512). The above methodology was tested on a large number of systems, such as the C60 molecule, diamond, Si and GaN supercells, and quantum molecular dynamics simulations for Si. Large-scale applications include a simulation of surface melting of Si and investigations of electronic and structural properties of surfaces, interfaces, and biomolecules. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 531–543, 1997}, number={5}, journal={International Journal of Quantum Chemistry}, author={Bernholc, Jerzy and Briggs, E. L. and Sullivan, D. J. and Brabec, C. J. and Nardelli, M. B. and Rapcewicz, K. and Roland, C. and Wensell, M.}, year={1997}, pages={531–543} }
 @article{nardelli_rapcewicz_bernholc_1997, title={Strain effects on the interface properties of nitride semiconductors}, volume={55}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.55.r7323}, abstractNote={An ab initio study of nitride-based heteroepitaxial interfaces that uses norm-conserving pseudopotentials and explicitly treats the strain due to lattice mismatch is presented. Strain effects on the band offsets range from 20% to 40%. The AlN/GaN/InN interfaces (with AlN in-plane lattice constant) are all of type I, while the ${\mathrm{Al}}_{0.5}$${\mathrm{Ga}}_{0.5}$N/AlN zinc-blende (001) interface is of type II. Further, the bulk polarizations in wurtzite AlN and GaN are -1.2 and -0.45 \ensuremath{\mu}C/${\mathrm{cm}}^{2}$, respectively, and the interface contribution to the polarization in the GaN/AlN wurtzite multiquantum-well is small.}, number={12}, journal={PHYSICAL REVIEW B}, author={Nardelli, MB and Rapcewicz, K and Bernholc, J}, year={1997}, month={Mar}, pages={R7323–R7326} }
 @article{nardelli_rapcewicz_bernholc_1997, title={Theory of interfaces and surfaces in wide-gap nitrides}, volume={15}, DOI={10.1116/1.589429}, abstractNote={A selection of the results of a theoretical investigation of the properties of interfaces and surfaces of the wide-gap III–V nitride semiconductors is reviewed. The electronic properties of wurtzite heteroepitaxial interfaces of AlN and GaN, incorporating the effects of strain, are discussed. In particular, we find that this interface is of type I and have calculated the valence-band offset to be −0.57 eV. The surface energies and atomic geometries of the 2×2 reconstructions of the (0001) face of GaN are also presented. In conditions which are rich in a given species, an adatom reconstruction of that species is found to be the most energetically favorable: for gallium-rich conditions, the reconstruction with a gallium adatom on a T3 site is the most stable, while for nitrogen-rich conditions the reconstruction with a nitrogen adatom on the H3 site is energetically the most favorable.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Nardelli, MB and Rapcewicz, K and Bernholc, J}, year={1997}, pages={1144–1147} }