(Color online) On the left scale it is indicated the confinement energy of the CB NW states as a function of the NW size. The blue dashed line is the fit obtained with Eq. (21) in the text, whereas the red dots represents the confinement energy of the lowest CB NW. The solid line refers to the right scale and it represents the projection of the c1 wave function onto the CB edge bulk state. The charge density of the CB state c1(s) for S = 6.5 nm is shown as an inset. 

(Color online) On the left scale it is indicated the confinement energy of the CB NW states as a function of the NW size. The blue dashed line is the fit obtained with Eq. (21) in the text, whereas the red dots represents the confinement energy of the lowest CB NW. The solid line refers to the right scale and it represents the projection of the c1 wave function onto the CB edge bulk state. The charge density of the CB state c1(s) for S = 6.5 nm is shown as an inset. 

Source publication
Article
Full-text available
We present a semiempirical pseudopotential method based on screened atomic pseudopotentials and derived from \textit{ab initio} calculations. This approach is motivated by the demand for pseudopotentials able to address nanostructures, where \textit{ab initio} methods are both too costly and insufficiently accurate at the level of the local-density...

Similar publications

Article
In this work we use a first-principles method based on the density functional theory, the full-potential linear augmented plane-wave method (FPLAPW), in order to calculate the electronic structures of the AlxGa1−xN alloys in the cubic modification. We adopt a model which allows the simulation of the composition x=0.0, 0.25, 0.50, 0.75 and 1.0. We o...

Citations

... However, these pseudopotentials lacked transferability across different structures. This issue was addressed by developing continuous pseudopotentials dependent on G vector lengths, enabling accurate calculations of electronic, optical, and transport properties in nanostructures using advanced computational methods [26,28,36,37]. ...
Preprint
Full-text available
The Semiempirical Pseudopotential Method (SEPM) has emerged as a valuable tool for accurately determining band structures, especially in the realm of low-dimensional materials. SEPM operates by utilizing atomic pseudopotentials, which are derived from DFT calculations. SEPM calculations offer a unique advantage compared to DFT as they eliminate the requirement for iterative self-consistent solutions in solving the Schr\"odinger equation, leading to a substantial reduction in computational complexity. The incorporation of both non-local and local Semiempirical Pseudopotentials in our current approach yields band structures and wavefunctions with enhanced precision compared to traditional empirical methods. When applied to monolayer TMDCs, adjusting the parameters to align with pertinent values obtained from DFT computations enables us to faithfully replicate the band structure, opening avenues for investigating the optoelectronic properties of TMDCs and exploring their potential applications in nanodevices.
... To understand the nature of potential, a set of form factors for the first few shells at a large number of additional reciprocal lattice vectors is needed. A variety of algebraic forms have been used in the past for bulk materials [40][41][42]. We have not found an existing form that has sufficient flexibility to obtain the correct band structure for 2D materials. ...
Article
Full-text available
We implemented a semi-empirical pseudopotential (SEP) method for calculating the band structures of graphene and graphene nanoribbons. The basis functions adopted are two-dimensional plane waves multiplied by several B-spline functions along the perpendicular direction. The SEP includes both local and non-local terms, which were parametrized to fit relevant quantities obtained from the first-principles calculations based on the density-functional theory (DFT). With only a handful of parameters, we were able to reproduce the full band structure of graphene obtained by DFT with a negligible difference. Our method is simple to use and much more efficient than the DFT calculation. We then applied this SEP method to calculate the band structures of graphene nanoribbons. By adding a simple correction term to the local pseudopotentials on the edges of the nanoribbon (which mimics the effect caused by edge creation), we again obtained band structures of the armchair nanoribbon fairly close to the results obtained by DFT. Our approach allows the simulation of optical and transport properties of realistic nanodevices made of graphene nanoribbons with very little computation effort.
... Fig. 3(b)]. Such linear polarization of a near-band-edge exciton state has commonly been realized in nanostructures of group II-VI with wurtzite structure, such as CdSe nanorods [49], ZnO QDs under hydrostatic pressure [23], CdSe dot-in-rod [50], and ZnO and GaN nanowires [51,52]. However, it has been rarely observed in QDs of group II-VI with zinc-blende structure. ...
Article
Colloidal quantum dots (QDs) of group II-VI are key ingredients of next-generation QD light-emitting diodes technology for display and lighting, yet the understanding of their luminescent characteristics are far from being mature. Using a hybrid time-dependent density functional theory, we have studied the electronic and excitonic properties of blue-emitting colloidal QDs within group II-VI containing a thousand atoms or more, including CdSe, CdS, ZnSe, and ZnS QDs, considering both quantum confinement and surface ligand effects. It is found that the calculated optical gaps are in excellent quantitative agreement with experiment, irrespective of the QD nature. Scaling laws of size-dependent energy gaps governed solely by quantum confinement effects have further been explored at both single-particle level and correlated excitonic level for all QDs. With concurrently stoichiometric control and enhancing quantum confinement effects, we have predicted an unusual switching of symmetry character of the highest occupied molecular orbital state from a Γ3 to a Γ1 symmetry at ultrasmall size (∼1 nm) for all QDs. After the switching, pronounced linearly polarized band-edge excitonic emission is activated. The radiative exciton decay lifetime is found to increase monotonically with increasing the QD size and tends to saturate at larger sizes. Finally, we have explored the surface passivation mechanism of inorganic chloride ligand, and identified various favorable Cd-Cl bonding configurations which enable an effective surface passivation resembling the commonly applied pseudohydrogen passivation scheme. We find that chloride ligand serves as a hole delocalization ligand and tends to redshift the absorption spectra, reduce the absorption intensity, and significantly enhance the exciton decay lifetime. Our results provide a guideline for spectroscopic studies of excitonic characteristics of colloidal QDs within group II-VI.
... In this respect band diagram shows appearance of bandgap across the Fermi level and is inversely proportional to diameters. Appearance of spurious band near the Fermi level due to undercoordinated lateral surface atom is general consequence for nanowire [16]. In the energy band diagram (FIGURE 2.) we have omitted the same after rigorous investigation and confirmation. ...
Conference Paper
CdTe rectangular nanowire of different diameter in zinc-blende phase is investigated using density functional theory. Enhancement of diameter increased stability and improved electronic qualities suitable for device purpose applications. Cohesive energy per atom enhanced on enlarging diameter advocating the stability. Large diameter nanowire (22.62Å) exhibits bandgap of 1.21eV and electronic effective mass is observed to be 0.51me. The bonding between Cd-Te atoms are predominantly observed as covalent assuring its inertness towards moisture.
Article
Direct Z-scheme heterojunctions are widely used for photocatalytic water splitting and CO 2 reduction by facilitating well-separated photogenerated charge carriers and spatial isolation of redox reactions. Here, using a facile two-step...
Article
Atomistic calculations of passivated nanostructures remain difficult due to the computational demands related to the high number of atoms to be typically considered. The empirical pseudopotential method (EPM) offers a good alternative in this sense, but finding trustable pseudopotentials for passivants in this method is still elusive. Following the idea of extracting nonspherically symmetric potentials from density functional theory (DFT) calculations, hydrogen pseudopotentials for silicon passivation are derived here and used to calculate the electronic states of low-dimensional structures within the EPM scheme. The single-particle Schrödinger equation is solved with the ensuing pseudopotentials for slabs with surfaces on the (111), (110), and (100) planes, as well as for passivated quantum dots and wires of different size. In all cases, the band gap is traced as a function of the sample size, showing good convergence towards the bulk value. For the slabs, the surface local density of states is also calculated and compared successfully to experiments. The derivation of the nonspherical pseudopotentials is based on an analytic formulation of the crystal potential and its connection to a series of DFT calculations, resulting in reliable, highly transferable and first-principles based passivant pseudopotentials to be used with the EPM.
Article
We propose a computational approach to combining the plane-wave method and the real-space treatment to describe the periodic variation in the material plane and the decay of wave functions from the material surfaces. The proposed approach is natural for two-dimensional material systems and thus may circumvent some intrinsic limitations involving the artificial replication of material layers in traditional supercell methods. In particular, we show that the proposed method is easy to implement and, especially, computationally effective since low-cost computational algorithms, such as iterative and recursive techniques, can be used to treat matrices with block tridiagonal structure. Using this approach we show first-principles features that supplement the current knowledge of some fundamental issues in bilayer graphene systems, including the coupling between the two graphene layers, the preservation of the σ band of monolayer graphene in the electronic structure of the bilayer system, and the differences in low-energy band structure between the AA- and AB-stacked configurations.
Article
We present a method to extract accurate pseudopotentials for surface passivants, within the framework of the atomic effective pseudopotential method. We retain the imaginary part of the pseudopotential in the construction procedure. This imaginary component in reciprocal space translates into a nonspherical component in real space. This asphericity allows to model surface dipoles and their ensuing band offsets. We show that these surface effects need to be taken into account to model electronic properties of quantum dots accurately—which requires to go beyond the spherical potential approximation for the passivant/surface atoms. The good level of transferability, without additional computational costs, is demonstrated for Si, CdSe, and InP nanostructures. The results are directly compared to large-scale density functional theory calculations.
Article
Full-text available
This work is focused on the dependence of electronic properties of wurtzite InAs [0001] nanowires on their size and under uniaxial strain using ab initio calculations. Diameter and strain are studied up to 3.0 nm and 8% respectively. We found that the band gap can be modulated by varying size of the nanowires and applying strain to nanowires. The band gap increases with the decrease in diameter of the wire and change in the band gap compared to bulk is directly proportional to 1/D2. There is an indirect–direct band gap transition with diameter and applied strain. The critical value of the diameter and strain for indirect-direct band gap transition is 2.0 nm and 5.5% strain respectively. This indirect-direct band gap transition can make InAs nanowires an optically active medium and hence useful in optoelectronics and light emitting devices.
Article
Full-text available
Using the atomistic pseudopotential method complemented by configuration interaction calculations, we have studied the electronic and optical properties of ZnO nanowires (NWs) in the presence of quantum confinement effects. Our results indicate that the near-band-edge exciton experiences a crossover from an in-plane polarized A-exciton (for D >= 3 nm) to an out-of-plane polarized C-exciton (for D < 3 nm) due to quantum confinement. This transition leads to a non-monotonic variation of Stokes shift, exhibiting a maximum value around the critical diameter of 3 nm. The observed behavior is analyzed by a stepwise inclusion of correlation effects, leading to a comprehensive description of the excitonic fine structure.