Multiscale Modeling of a Quantum Dot Heterostructure

2011 ◽  
Vol 1370 ◽  
Author(s):  
P. Sengupta ◽  
S. Lee ◽  
S. Steiger ◽  
H. Ryu ◽  
G. Klimeck
Keyword(s):  
Optical Transition ◽  
Tight Binding ◽  
Integrated Approach ◽  
Multiscale Approach ◽  
Multiscale Simulations ◽  
Numerical Accuracy ◽  
Structure Description ◽  
Valence Bands ◽  
Proper Splitting ◽  
Computational Resources

ABSTRACTA multiscale approach was adopted for the calculation of confined states in self-assembled semiconductor quantum dots (QDs). While results close to experimental data have been obtained with a combination of atomistic strain and tight-binding (TB) electronic structure description for the confined quantum states in the QD, the TB calculation requires substantial computational resources. To alleviate this problem an integrated approach was adopted to compute the energy states from a continuum 8-band k.p Hamiltonian under the influence of an atomistic strain field. Such multiscale simulations yield a roughly six-fold faster simulation. Atomic-resolution strain is added to the k.p Hamiltonian through interpolation onto a coarser continuum grid. Sufficient numerical accuracy is obtained by the multiscale approach. Optical transition wavelengths are within 7% of the corresponding TB results with a proper splitting of p-type sub-bands. The systematically lower emission wavelengths in k.p are attributable to an underestimation of the coupling between the conduction and valence bands.

Theory of chemically induced kink formation on cracks in silica. II. Force law calculations

1987 ◽  
Vol 2 (5) ◽  
pp. 631-637 ◽  
Author(s):  
K. Masuda-Jindo ◽  
V. K. Tewary ◽  
Robb Thomson
Keyword(s):  
Tight Binding ◽  
High Peak ◽  
Bond Breaking ◽  
Dimensional Chain ◽  
Numerical Accuracy ◽  
Long Tail ◽  
One Dimensional ◽  
Crack Motion ◽  
Chemically Induced ◽  
Assisted Fracture

This article is this second of a pair on a theory of chemically assisted fracture. In it a simple bond orbital model of the force laws to be used in fracture is developed. In the bond orbital model, only a few of the atoms in the vicinity of the bond to be broken are considered and do not include interactions with the rest of the system, which is assumed to be Newtonian. Numerical accuracy is not required, but qualitative features of the force laws are believed to be valid. The silica bond is shown to rise quickly to a high peak, after which it develops a relatively long tail. When the bond is attacked by water, modeling by the same technique indicates that the bond has a “snapping” characteristic that is important in the theory developed in the first article. For bonds with smooth “back sides” the barriers to crack motion are shown to be low, but barriers are expected to be observable when the bond snaps. A tight binding treatment of a one-dimensional chain has been included in order to investigate the effect of including band effects in the force law. These effects are found to be small compared to the simple bond breaking of the bond orbital calculation.

Local Structural Changes Around Charged Dangling Bonds

1996 ◽  
Vol 420 ◽  
Author(s):  
R. Biswas ◽  
Qiming Li
Keyword(s):  
Energy Minimization ◽  
Local Structure ◽  
Structural Changes ◽  
Nearest Neighbor ◽  
Energy Surface ◽  
Optical Transition ◽  
Tight Binding ◽  
Dangling Bond ◽  
Fast Relaxation ◽  
Minimization Procedure

AbstractTight-binding total energy calculations are used to describe the changes in local structure following either electron or hole capture by a neutral dangling bond in computer generated a-Si:H models. After the change in charge state, the structure is allowed to relax by a steepest descent energy minimization procedure. Generally the local bond angles increase (decrease) rapidly by 3- 100 in transitions from the D0 to the D+ (D-) configurations. The displacement of nearest neighbor atoms and nearby H atoms is large (more than 0.2 Å), but displacement of distant atoms is generally much smaller. Calculated optical transition levels have the D- level below D0 and the D+ level above D0. The fast relaxation of the charged defect configurations suggest a smooth energy surface for the relaxation.

ELEMENTARY EXCITATIONS AND OPTICAL ABSORPTION IN A POLYACENE CHAIN

2003 ◽  
Vol 17 (10) ◽  
pp. 2023-2034 ◽  
Author(s):  
Z. AN ◽  
C. Q. WU
Keyword(s):  
Optical Absorption ◽  
Tight Binding ◽  
Electronic States ◽  
Open Boundary ◽  
Aromatic Rings ◽  
Open Boundary Condition ◽  
Elementary Excitations ◽  
Strongly Coupled ◽  
Valence Bands ◽  
Doubly Charged

Within a tight-binding Su–Schrieffer–Heeger model, the elementary excitations and optical absorption of a polyacene chain are investigated. The polyacene chain composed of a number of aromatic rings is considered as two strongly coupled polyacetylene chains with an open boundary condition. First of all we found an interchain-coupled neutral soliton in a pristine chain as a consequence of odd-number sites in each chain. There are two localized electronic states accompanying the soliton and appearing in the conduction and valence bands, respectively. Moreover, an injected electron or hole will induce a polaron-like deformation mixed with the interchain soliton, while two extra electrons or holes will result in three separate solitons, among which one is doubly charged and other two are neutral. The optical absorption due to these elementary excitations are obtained.

Tight-Binding Model for Zn3As2 Valence Bands

1992 ◽  
Vol 173 (2) ◽  
pp. K25-K28 ◽  
Author(s):  
K. Sierański ◽  
Szatkowski
Keyword(s):  
Tight Binding ◽  
Tight Binding Model ◽  
Binding Model ◽  
Valence Bands

Electronic Theory of Mn - Alloyed Diluted Magnetic Semiconductors

1986 ◽  
Vol 89 ◽  
Author(s):  
H. Ehrenreich ◽  
K. C. Hass ◽  
B. E. Larson ◽  
N. F. Johnson
Keyword(s):  
Diluted Magnetic Semiconductors ◽  
Magnetic Semiconductors ◽  
Tight Binding ◽  
Magnetic Interactions ◽  
Potential Approximation ◽  
Exchange Constants ◽  
Density Band ◽  
Level Model ◽  
Diluted Magnetic ◽  
Valence Bands

AbstractRecent calculations of the electronic structure and magnetic interactions in Mn - alloyed II-VI diluted magnetic semiconductors (DMS) are summarized. Detailed band structure results are obtained using an empirical tight-binding, coherent potential approximation approach with input from experiment and local spin density band calculations. The dominant magnetic interactions in these systems result from hybridization between spin-split Mn d states and sp valence bands. Superexchange between Mn moments is well described by a simple three-level model which yields accurate Mn - Mn exchange constants for a variety of II-VI DMS as well as the rocksalt insulators MnO and α-MnS.

scholarly journals Protein engineering by highly parallel screening of computationally designed variants

2016 ◽  
Vol 2 (7) ◽  
pp. e1600692 ◽  
Author(s):  
Mark G. F. Sun ◽  
Moon-Hyeong Seo ◽  
Satra Nim ◽  
Carles Corbi-Verge ◽  
Philip M. Kim
Keyword(s):  
Protein Engineering ◽  
Protein Design ◽  
Tight Binding ◽  
Integrated Approach ◽  
Selection Strategies ◽  
Selection Systems ◽  
Protein Properties ◽  
Protein Binders

Current combinatorial selection strategies for protein engineering have been successful at generating binders against a range of targets; however, the combinatorial nature of the libraries and their vast undersampling of sequence space inherently limit these methods due to the difficulty in finely controlling protein properties of the engineered region. Meanwhile, great advances in computational protein design that can address these issues have largely been underutilized. We describe an integrated approach that computationally designs thousands of individual protein binders for high-throughput synthesis and selection to engineer high-affinity binders. We show that a computationally designed library enriches for tight-binding variants by many orders of magnitude as compared to conventional randomization strategies. We thus demonstrate the feasibility of our approach in a proof-of-concept study and successfully obtain low-nanomolar binders using in vitro and in vivo selection systems.

Tight-binding model for Zn3P2 valence bands

1993 ◽  
Vol 88 (8) ◽  
pp. 663-666 ◽  
Author(s):  
K. Sierański ◽  
J. Szatkowski
Keyword(s):  
Tight Binding ◽  
Tight Binding Model ◽  
Binding Model ◽  
Valence Bands

Silicene dynamic optical response in the presence of external electric and exchange fields

2021 ◽  
Author(s):  
Maryam Mirzaei ◽  
Taraneh Vazifehshenas ◽  
T. Salavati-fard ◽  
Bilal Tanatar
Keyword(s):  
Optical Transition ◽  
Dominant Role ◽  
Incident Light ◽  
Tight Binding ◽  
Polarized Light ◽  
Initial Point ◽  
Optical Response ◽  
Longitudinal Optical ◽  
Binding Model ◽  
Optical Responses

Abstract We investigate the dynamic optical transition of monolayer silicene in the presence of external electric and exchange fields within the low-energy tight-binding model. Applying external electric and exchange fields breaks the silicene band structure spin and valley degeneracies. Three phases of silicene corresponding to different strengths of perpendicular electric field with respect to the spin-orbit coupling (∆z < ∆so, ∆z = ∆so and ∆z > ∆so) are considered. We obtain the spinand valley-dependent optical responses to the incoming circularly polarized light using the Kubo formula. We show and discuss how the magnitude and direction of the transverse and longitudinal optical responses of such a system change with the electric and exchange fields. Our calculations suggest that the intraband part of the longitudinal optical response as well as the initial point of the interband part have strong dependencies on the exchange field. Furthermore, we show that one of the spin subbands plays a dominant role in the response to polarized light. Depending on the type of incident light polarization, the dominant subband may change. Our results shed light on the relation between silicene dynamic optical responses and externally applied fields.

scholarly journals Multiscale Discrete Element Modeling

Symmetry ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 219
Author(s):  
Andrew A. Zhuravlev ◽  
Karine K. Abgaryan ◽  
Dmitry L. Reviznikov
Keyword(s):  
Polycrystalline Silicon ◽  
Reference Data ◽  
Discrete Element ◽  
Quantum Mechanical ◽  
Multiscale Approach ◽  
Multiscale Simulations ◽  
Discrete Element Modeling ◽  
Element Modeling ◽  
Consistent Manner ◽  
Using Data

A multiscale approach to discrete element modeling is presented. A distinctive feature of the method is that each macroscopic discrete element has an associated atomic sample representing the material’s atomic structure. The dynamics of the elements on macro and micro levels are described by systems of ordinary differential equations, which are solved in a self-consistent manner. A full cycle of multiscale simulations is applied to polycrystalline silicon. Macroscale elastic properties of silicon were obtained only using data extracted from the quantum mechanical properties. The results of computational experiments correspond well to the reference data.

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