The Experts below are selected from a list of 6312 Experts worldwide ranked by ideXlab platform
James R Chelikowsky - One of the best experts on this subject based on the ideXlab platform.
-
real space Pseudopotential Method for computing the vibrational stark effect
Journal of Chemical Physics, 2016Co-Authors: Benjamin Garrett, Leeor Kronik, Ido Azuri, James R ChelikowskyAbstract:The vibrational Stark shift is an important effect in determining the electrostatic environment for molecular or condensed matter systems. However, accurate ab initio calculations of the vibrational Stark effect are a technically demanding challenge. We make use of density functional theory constructed on a real-space grid to expedite the computation of this effect. Our format is especially advantageous for the investigation of small molecules in finite fields as cluster boundary conditions eliminate spurious supercell interactions and allow for charged systems, while convergence is controlled by a single parameter, the grid spacing. The Stark tuning rate is highly sensitive to the interaction between anharmonicity in a vibrational mode and the applied field. To ensure this subtle interaction is fully captured, we apply three parallel approaches: a direct finite field, a perturbative Method, and a molecular dynamics Method. We illustrate this Method by applying it to several small molecules containing C–O...
-
real space Pseudopotential Method for first principles calculations of general periodic and partially periodic systems
Physical Review B, 2008Co-Authors: Amir Natan, Murilo L Tiago, Leeor Kronik, Ayelet Benjamini, Doron Naveh, Scott P Beckman, James R ChelikowskyAbstract:We present a real-space Method for electronic-structure calculations of systems with general full or partial periodicity. The Method is based on the self-consistent solution of the Kohn-Sham equations, using first principles Pseudopotentials, on a uniform three-dimensional non-Cartesian grid. Its efficacy derives from the introduction of a new generalized high-order finite-difference Method that avoids the numerical evaluation of mixed derivative terms and results in a simple yet accurate finite difference operator. Our Method is further extended to systems where periodicity is enforced only along some directions (e.g., surfaces), by setting up the correct electrostatic boundary conditions and by properly accounting for the ion-electron and ion-ion interactions. Our Method enjoys the main advantages of real-space grid techniques over traditional plane-wave representations for density functional calculations, namely, improved scaling and easier implementation on parallel computers, as well as inherent immunity to spurious interactions brought about by artificial periodicity. We demonstrate its capabilities on bulk GaAs and Na for the fully periodic case and on a monolayer of Si-adsorbed polar nitrobenzene molecules for the partially periodic case.
-
size limits on doping phosphorus into silicon nanocrystals
Nano Letters, 2008Co-Authors: Tzuliang Chan, Murilo L Tiago, Efthimios Kaxiras, James R ChelikowskyAbstract:We studied the electronic properties of phosphorus-doped silicon nanocrystals using the real-space first-principles Pseudopotential Method. We simulated nanocrystals with a diameter of up to 6 nm and made a direct comparison with experimental measurement for the first time for these systems. Our calculated size dependence of hyperfine splitting was in excellent agreement with experimental data. We also found a critical nanocrystal size below which we predicted that the dopant will be ejected to the surface.
-
real space Pseudopotential Method for computing the electronic properties of periodic systems
Physical Review B, 2004Co-Authors: M M G Alemany, Manish Jain, Leeor Kronik, James R ChelikowskyAbstract:We present a real-space Method for electronic-structure calculations of periodic systems. Our Method is based on the self-consistent solution of the Kohn-Sham equations on a uniform three-dimensional grid. A higher-order finite-difference Method is combined with ab initio Pseudopotentials. The kinetic energy operator, the nonlocal term of the ionic Pseudopotential, and the Hartree and exchange-correlation potentials are set up directly on the real-space grid. The local contribution to the ionic Pseudopotential is initially obtained in reciprocal space and is then transferred to the real-space grid by Fourier transform. Our Method enjoys the main advantages of real-space grid techniques over traditional plane-wave representations for density-functional calculations, i.e., improved scaling and easier implementation on parallel computers. We illustrate the Method by application to liquid silicon.
-
quantum confinement in phosphorus doped silicon nanocrystals
Physical Review Letters, 2004Co-Authors: Dmitriy V Melnikov, James R ChelikowskyAbstract:Electronic properties of phosphorus donors in hydrogenated silicon nanocrystals are investigated using a real-space ab initio Pseudopotential Method for systems with up to 500 atoms. We present calculations for the ionization energy, binding energy, and electron density associated with the doped nanocrystal. We find that the ionization energy for the nanocrystal is virtually independent of size. This behavior may be attributed to localization of the electron around the impurity site owing to a large electron-impurity interaction within confined systems. In contrast to this result, the calculated hyperfine splitting exhibits a strong size dependence. For small nanocrystals it greatly exceeds the bulk value. This finding agrees with recent experimental measurements.
Alex Zunger - One of the best experts on this subject based on the ideXlab platform.
-
predicting interband transition energies for inas gasb superlattices using the empirical Pseudopotential Method
Physical Review B, 2003Co-Authors: Rita Magri, Alex ZungerAbstract:Recent measurements surprisingly show that the lowest valence-to-conduction confined transitions in narrow $(\mathrm{InAs}{)}_{8}/(\mathrm{GaSb}{)}_{n}$ and $(\mathrm{InAs}{)}_{6}/(\mathrm{GaSb}{)}_{n}$ superlattices increase in energy as the barrier thickness n increases. We show that in addition to the mesoscopic geometric quantities (well and barrier sizes), an atomic-scale description of interdiffused interfaces is needed to correctly reproduce the observed spectroscopic trend. The interdiffused interface is modeled via diffusion equations. We compare our atomistic empirical Pseudopotential calculation in which only the bulk binary data are fit to experiment, with contemporary Methods in which agreement with experiment is forced using ideally abrupt interfaces.
-
Pseudopotential calculation of the excitonic fine structure of million atom self assembled in 1 x ga x a s g a a s quantum dots
Physical Review B, 2003Co-Authors: Gabriel Bester, Selvakumar V Nair, Alex ZungerAbstract:The atomistic Pseudopotential Method is used to accurately predict the electron-hole exchange-induced fine structure (FS) and polarization anisotropy in million-atom ${\mathrm{In}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ quantum dots of various shapes and compositions. The origin of the FS splittings is clarified using a simple model where the effects of atomistic symmetry and spin-orbit interaction are separately evident. Remarkably, polarization anisotropy and FS splittings are shown to occur, even in a cylindrically symmetric dot. Furthermore, ``dark excitons'' are predicted to be partially allowed. Trends in splittings among different shapes and compositions are revealed.
-
Pseudopotential calculations of nanoscale cdse quantum dots
Physical Review B, 1996Co-Authors: Linwang Wang, Alex ZungerAbstract:A plane-wave semiempirical Pseudopotential Method with nonlocal potentials and spin-orbit coupling is used to calculate the electronic structure of surface-passivated wurtzite CdSe quantum dots with up to 1000 atoms. The calculated optical absorption spectrum reproduces the features of the experimental results and the exciton energies agree to within \ensuremath{\sim}0.1 eV over a range of dot sizes. The correct form of Coulomb interaction energy with size-dependent dielectric constant is found to be essential for such good agreement. \textcopyright{} 1996 The American Physical Society.
Yousef Saad - One of the best experts on this subject based on the ideXlab platform.
-
higher order finite difference Pseudopotential Method an application to diatomic molecules
Physical Review B, 1994Co-Authors: James R Chelikowsky, N Troullier, Yousef SaadAbstract:We present a prescription for performing electronic-structure calculations without the explicit use of a basis. Our prescription combines a higher-order finite-difference Method with ab initio Pseudopotentials. In contrast to Methods that combine a plane-wave basis with Pseudopotentials, our calculations are performed completely in real space. No artifacts such as supercell geometries need be introduced for localized systems. Although this approach is easier to implement than one that employs a plane-wave basis, no loss of accuracy occurs. We apply this Method to calculate the structural and electronic properties of several diatomic molecules: ${\mathrm{Si}}_{2}$, ${\mathrm{C}}_{2}$, ${\mathrm{O}}_{2}$, and CO.
-
finite difference Pseudopotential Method electronic structure calculations without a basis
Physical Review Letters, 1994Co-Authors: James R Chelikowsky, N Troullier, Yousef SaadAbstract:We present a Method for performing electronic structure calculations without the explicit use of a basis. We combine a finite-difference approach with ab initio Pseudopotentials. In contrast to Methods which use a plane wave basis, our calculations are performed completely in ``real space.'' No artifacts such as supercell geometries need be introduced for localized systems. Although this approach is easier to implement than one with a plane wave basis, no loss of accuracy occurs. The electronic structure of several diatomic molecules, ${\mathrm{Si}}_{2}$, ${\mathrm{C}}_{2}$, ${\mathrm{O}}_{2}$, and CO, are calculated to illustrate the utility of this Method.
M. L. Tilton - One of the best experts on this subject based on the ideXlab platform.
-
Pseudopotential Methods for Superlattices: Applications to Mid-Infrared Semiconductor Lasers
MRS Online Proceedings Library, 2000Co-Authors: G. C. Dente, M. L. TiltonAbstract:Calculations of optoelectronic properties for superlattice materials require accurate subband energies, wavefunctions and radiative matrix elements. We have recently begun using a solution Method based on the Empirical Pseudopotential Method, or EPM. This Method shows particular strength in analyzing structures with short periods or thin layers, for which the standard Method, based on k→⊙p→ perturbation theory and the envelope function approximation, may be problematical. We will describe the EPM applied to bulk solids and then demonstrate our direct generalization of the Method for applications to superlattice structures. Finally, we will apply the EPM Method to several type II superlattice samples and compare the predictions to absorbance spectroscopy data.
-
Pseudopotential Methods for superlattices applications to mid infrared semiconductor lasers
Journal of Applied Physics, 1999Co-Authors: G. C. Dente, M. L. TiltonAbstract:Many mid-infrared semiconductor laser sources are now being developed with superlattice active regions. Calculations of gain, index of refraction, and intervalence subband absorption for these laser materials require accurate subband energies, wave functions, and radiative matrix elements. We have recently begun using a solution Method based on the empirical Pseudopotential Method (EPM). This Method shows particular strength in analyzing structures with short periods or thin layers, for which the standard Method, based on k⋅p perturbation theory and the envelope function approximation, may be problematical. We will describe the EPM applied to bulk solids and then demonstrate our direct generalization of the Method for applications to superlattice structures. Calculations for recently developed mid-infrared semiconductor lasers using type-II superlattice active regions will be used to illustrate the Method.
Leeor Kronik - One of the best experts on this subject based on the ideXlab platform.
-
real space Pseudopotential Method for computing the vibrational stark effect
Journal of Chemical Physics, 2016Co-Authors: Benjamin Garrett, Leeor Kronik, Ido Azuri, James R ChelikowskyAbstract:The vibrational Stark shift is an important effect in determining the electrostatic environment for molecular or condensed matter systems. However, accurate ab initio calculations of the vibrational Stark effect are a technically demanding challenge. We make use of density functional theory constructed on a real-space grid to expedite the computation of this effect. Our format is especially advantageous for the investigation of small molecules in finite fields as cluster boundary conditions eliminate spurious supercell interactions and allow for charged systems, while convergence is controlled by a single parameter, the grid spacing. The Stark tuning rate is highly sensitive to the interaction between anharmonicity in a vibrational mode and the applied field. To ensure this subtle interaction is fully captured, we apply three parallel approaches: a direct finite field, a perturbative Method, and a molecular dynamics Method. We illustrate this Method by applying it to several small molecules containing C–O...
-
real space Pseudopotential Method for first principles calculations of general periodic and partially periodic systems
Physical Review B, 2008Co-Authors: Amir Natan, Murilo L Tiago, Leeor Kronik, Ayelet Benjamini, Doron Naveh, Scott P Beckman, James R ChelikowskyAbstract:We present a real-space Method for electronic-structure calculations of systems with general full or partial periodicity. The Method is based on the self-consistent solution of the Kohn-Sham equations, using first principles Pseudopotentials, on a uniform three-dimensional non-Cartesian grid. Its efficacy derives from the introduction of a new generalized high-order finite-difference Method that avoids the numerical evaluation of mixed derivative terms and results in a simple yet accurate finite difference operator. Our Method is further extended to systems where periodicity is enforced only along some directions (e.g., surfaces), by setting up the correct electrostatic boundary conditions and by properly accounting for the ion-electron and ion-ion interactions. Our Method enjoys the main advantages of real-space grid techniques over traditional plane-wave representations for density functional calculations, namely, improved scaling and easier implementation on parallel computers, as well as inherent immunity to spurious interactions brought about by artificial periodicity. We demonstrate its capabilities on bulk GaAs and Na for the fully periodic case and on a monolayer of Si-adsorbed polar nitrobenzene molecules for the partially periodic case.
-
real space Pseudopotential Method for computing the electronic properties of periodic systems
Physical Review B, 2004Co-Authors: M M G Alemany, Manish Jain, Leeor Kronik, James R ChelikowskyAbstract:We present a real-space Method for electronic-structure calculations of periodic systems. Our Method is based on the self-consistent solution of the Kohn-Sham equations on a uniform three-dimensional grid. A higher-order finite-difference Method is combined with ab initio Pseudopotentials. The kinetic energy operator, the nonlocal term of the ionic Pseudopotential, and the Hartree and exchange-correlation potentials are set up directly on the real-space grid. The local contribution to the ionic Pseudopotential is initially obtained in reciprocal space and is then transferred to the real-space grid by Fourier transform. Our Method enjoys the main advantages of real-space grid techniques over traditional plane-wave representations for density-functional calculations, i.e., improved scaling and easier implementation on parallel computers. We illustrate the Method by application to liquid silicon.
