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Author

Daniel P. Joubert

Bio: Daniel P. Joubert is a academic researcher from University of the Witwatersrand. The author has contributed to research in topic(s): Density functional theory & Phonon. The author has an hindex of 11, co-authored 82 publication(s) receiving 46853 citation(s). Previous affiliations of Daniel P. Joubert include Technical University of Kenya & Umaru Musa Yar'adua University.

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Topics: Density functional theory, Phonon, Band gap ...read more
Papers
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Journal ArticleDOI: 10.1103/PHYSREVB.59.1758
Georg Kresse1, Daniel P. Joubert2Institutions (2)
15 Jan 1999-Physical Review B
Abstract: The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Bl\"ochl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules $({\mathrm{H}}_{2}{,\mathrm{}\mathrm{H}}_{2}{\mathrm{O},\mathrm{}\mathrm{Li}}_{2}{,\mathrm{}\mathrm{N}}_{2}{,\mathrm{}\mathrm{F}}_{2}{,\mathrm{}\mathrm{BF}}_{3}{,\mathrm{}\mathrm{SiF}}_{4})$ and several bulk systems (diamond, Si, V, Li, Ca, ${\mathrm{CaF}}_{2},$ Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.

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Topics: Cauchy stress tensor (53%)

46,297 Citations


BookDOI: 10.1007/BFB0106730
01 Jan 1998-
Topics: Intracule (75%), Orbital-free density functional theory (74%), Density functional theory (73%) ...read more

135 Citations


Journal ArticleDOI: 10.1016/J.DIAMOND.2010.11.021
Abstract: Bulk properties and stability of the entire series of group 4d transition metal carbides and nitrides are reported in this work. The theoretical calculations were carried out within Local Density Approximation and Generalized Gradient Approximation using the Perdew, Burke and Ernzerhof exchange correlation functional. The generalized gradient approximation predictions were found to be closer to experimental values than the local density approximation predictions. In particular, LDA predictions were found to overestimate bulk moduli properties by as much as 5.6–11.5% while equilibrium lattice constants were found to be underestimated by as much as 0.2–5% compared to experimental values. On the other hand, GGA calculations were found to overestimate the lattice parameters by 0.2–6.9%, while underestimating the bulk moduli by as much as 0.07–5%. Out of the carbides considered, TcC and RuC were found to have the highest values of bulk moduli while YC and CdC had the lowest. Similarly, out of the nitrides, MoN and TcN were found to exhibit the largest bulk moduli, indicating that they were the hardest, while CdN had the lowest value and hence relatively softer. Overall, the nitrides presented higher values of bulk moduli than the carbides, an observation that is well supported by their correspondingly shorter bondlengths. The cohesive and structural properties of the 4d transition metal carbides and nitrides are also reported.

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49 Citations


Journal ArticleDOI: 10.1103/PHYSREVB.84.094110
Mahlaga P. Molepo1, Daniel P. Joubert1Institutions (1)
19 Sep 2011-Physical Review B
Abstract: We use first-principles calculations based on density functional theory to study the structural properties and pressure-induced solid-solid phase transitions of ZnO. Both the local-density and the generalized gradient approximations are employed together with the projector augmented wave potentials to mimic the electron-ion interaction. We consider the wurtzite (B4), rocksalt (B1), zinc blende (B3), CsCl (B2), NaTl (B32), WC (B${}_{h}$), BN (B${}_{k}$), NiAs (B8${}_{1}$), and AsTi (B${}_{i}$) modifications of ZnO. The calculated structural properties in the B4, B3, B1, and B2 phases are in excellent agreement with earlier ab initiopredictions, as is the transition pressure between them. We find that the B4 phase is the most preferred low-pressure candidate in ZnO while the B2 phase is favorable at high pressures. Apart from the previously reported $B4\ensuremath{\rightarrow}B1\ensuremath{\rightarrow}B2$ phase transition, our study reveals other possible paths for a transition from the B4 to the B2 phase.

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33 Citations


Journal ArticleDOI: 10.1140/EPJB/E2015-50478-X
Abstract: First principles density functional theory (DFT) calculations for bulk structural, electronic and optical properties of ternary compounds AgAlX2 (X = S, Se, Te) were performed with two flavours of generalised gradient approximations (PBE and PBEsol) and the hybrid functional HSE06. Using cohesive energy as a stability criterion, we found that the chalcopyrite structure is the favoured phase for these materials. PBEsol gives structural properties closer to the experimental values when compared to the results of PBE. Tetragonal distortion and anion displacement were calculated and we found them to be the cause of the crystal field splitting. Reduction of the bandgap and band splitting around the Γ in the Brillouin zone was noted when spin-orbit coupling was included in our study especially in the case of AgAlTe2. The HSE06 bandgap and frequency dependent dielectric function were in very good agreement with experimental results. We have also shown that the maximum absorption peak lies in the ultraviolet range irrespective of the functional used. The refractive index is also discussed.

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30 Citations


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Open accessJournal ArticleDOI: 10.1136/BMJ.323.7325.1375/A

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08 Dec 2001-BMJ
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

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30,199 Citations


Open accessJournal ArticleDOI: 10.1088/0953-8984/21/39/395502
Paolo Giannozzi1, Stefano Baroni2, Stefano Baroni3, Nicola Bonini4  +37 moreInstitutions (13)
Abstract: QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.

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Topics: Quantum ESPRESSO (66%), Espresso (56%)

15,767 Citations


Journal ArticleDOI: 10.1063/1.478522
Abstract: We present an analysis of the performances of a parameter free density functional model (PBE0) obtained combining the so called PBE generalized gradient functional with a predefined amount of exact exchange. The results obtained for structural, thermodynamic, kinetic and spectroscopic (magnetic, infrared and electronic) properties are satisfactory and not far from those delivered by the most reliable functionals including heavy parameterization. The way in which the functional is derived and the lack of empirical parameters fitted to specific properties make the PBE0 model a widely applicable method for both quantum chemistry and condensed matter physics.

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11,131 Citations


Open accessJournal ArticleDOI: 10.1088/0953-8984/14/11/301
Abstract: First-principles simulation, meaning density-functional theory calculations with plane waves and pseudopotentials, has become a prized technique in condensed-matter theory. Here I look at the basics of the suject, give a brief review of the theory, examining the strengths and weaknesses of its implementation, and illustrating some of the ways simulators approach problems through a small case study. I also discuss why and how modern software design methods have been used in writing a completely new modular version of the CASTEP code.

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Topics: CASTEP (50%)

8,251 Citations


Open accessJournal ArticleDOI: 10.1038/NNANO.2014.35
Likai Li1, Yijun Yu1, Guo Jun Ye2, Q. Q. Ge1  +5 moreInstitutions (2)
Abstract: Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.

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Topics: Phosphorene (55%), Field-effect transistor (53%)

5,801 Citations


Performance
Metrics

Author's H-index: 11

No. of papers from the Author in previous years
YearPapers
20215
20205
20199
20189
20171
20164

Top Attributes

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Author's top 5 most impactful journals

European Physical Journal B

12 papers, 101 citations

Physical Review A

11 papers, 33 citations

arXiv: Materials Science

10 papers, 6 citations

Materials today communications

6 papers, 12 citations

Journal of Chemical Physics

6 papers, 44 citations

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