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Revisiting the structures and energies of silicon ?110? symmetric tilt grain boundaries
摘要： Atomistic simulations of 18 silicon ?110? symmetric tilt grain boundaries are performed using Stillinger Weber, Tersoff, and the optimized Modified Embedded Atom Method potentials. We define a novel structural unit classification through dislocation core analysis to characterize the relaxed GB structures. GBs with the misorientation angle h ranging from 13.44° to 70.53° are solely composed of Lomer dislocation cores. For GBs with h less than but close to 70.53°, GB 'step' appears and the equilibrated states with lowest GB energies can be attained only when such GB 'step' is located in the middle of each single periodic GB structure. For the misorientation angles in the range of 93.37° ￡ h ￡ 148.41°, GB structures become complicated since they contain multiple types of dislocation cores. This work not only facilitates the structural characterization of silicon ?110? STGBs, but also may provide new insights into mirco-structure design in multicrystalline silicon.
关键词： silicon,structural units,energies,grain boundaries,atomistic simulations,dislocation cores
更新于2025-09-23 15:22:29
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Generalized gradient approximation exchange energy functional with near-best semilocal performance
摘要： We develop and validate a non-empirical generalized gradient approximation (GGA) exchange (X) density functional which performs as well as the SCAN meta-GGA on standard thermochemistry tests. Additionally, the new functional (“NCAP”) yields Kohn-Sham eigenvalues that are useful approximations of the density functional theory (DFT) ionization potential theorem values by inclusion of a systematic derivative discontinuity shift of the X potential. NCAP also enables time-dependent DFT (TD-DFT) calculations of good quality polarizabilities, hyper-polarizabilities, and one-fermion excited states without modification (calculated or ad hoc) of the long-range behavior of the exchange potential or other patches. NCAP is constructed by reconsidering the imposition of the asymptotic correctness of the X potential (-1/r) as a constraint. Inclusion of derivative discontinuity and approximate integer self-interaction correction treatments along with first-principles determination of the effective second-order gradient expansion coefficient yields a major advance over our earlier correct asymptotic potential functional [“CAP”; J. Chem. Phys. 142, 054105 (2015)]. The new functional reduces a spurious bump in the CAP atomic exchange potential and moves it to distances irrelevantly far from the nucleus (outside the tail of essentially all practical basis functions). It therefore has nearly correct atomic exchange-potential behavior out to rather large finite distances r from the nucleus but eventually goes as ? c / r with an estimated value for the constant c of around 0.3, so as to achieve other important properties of exact DFT exchange within the restrictions of the GGA form. We illustrate the results with the Ne atom optimized effective potentials and with standard molecular benchmark test data sets for thermochemical, structural and response properties.
关键词： hyperpolarizabilities,excitation energies,Density functional theory,exchange potential asymptotic behavior,polarizabilities,exchange-correlation functional
更新于2025-09-23 15:21:21
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Late-stage Customization in Volume Production of Organic Photovoltaics
摘要： Organic photovoltaics (OPV) in free-form shapes have become a unique feature compared to other thin-film photovoltaic technologies. The ability to conform coated layers to any form of shape or structure is a game changer for OPV and creates a paradigm shift in conventional energy businesses. As urban growth prevails, the energy requirement must be compensated by modern means and OPVs provide unique properties where its form or shape can be fully customized. This creates a synergy as they are then easily integrated onto structures or even products. By doing so not only the space requirements are diminished but the energy is delivered directly to the point of use rather than having them transported from central harvesting. The present communication discusses the advances in realizing such free-from patterns by structuring the functional layers to shape after they have been deposited which is referred to as late-stage customization. Using this approach, a pre-coated generic OPV material can be converted into any design upon customer request. The advantages include easier planning, shorter lead times in production as well as paving the way towards lean manufacturing.
关键词： renewable energies,mass production,organic photovoltaics (OPV),laser scribing,slot-die coating,module customization,roll-to-roll fabrication,dielectric material
更新于2025-09-23 15:21:01
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Excitonic complexes in InAs/InP nanowire quantum dots
摘要： InAs quantum dots embedded in InP nanowires form an important platform for basic research studies, as well as for quantum dot applications. Notably, understanding of nanowire quantum dot spectral properties is essential in both cases. Therefore, in this work we use atomistic theory to study spectra of the single exciton (X ), the biexciton (X X ), the triexciton (X X X ), and the positively and negatively charged trions (X + and X ?) con?ned in these nanostructures. We focus on the role of vertical and lateral con?nement, therefore, we systematically study a large family of quantum dots with different heights and diameters, and ?nd the important role of correlations due to presence of higher states. We ?nd that the order of excitonic binding energies is a characteristic feature of InAs/InP nanowire quantum dots being (ordered from negative to positive values): X ?, X X , and X +, with strongly bound X ?, rather weakly bound X X , and typically unbound X +. Next, we determine the key role of alloy randomness due to intermixing, which turns out to especially important for larger quantum dot heights and phosphorous contents over 40%. In selected cases, the alloying can lead to an unbound biexciton, and can even reverse ordering of excitonic lines.
关键词： InAs/InP nanowire quantum dots,atomistic theory,binding energies,alloy randomness,excitonic complexes
更新于2025-09-23 15:21:01
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Nested control loop design for differential boost inverter using generalized averaged model in photovoltaic applications
摘要： To use photovoltaic energy, voltage source inverters are playing an important role. The most of local AC loads such as AC motors need higher voltage than solar panel output voltage. Differential boost inverter produces an AC voltage that is greater than the DC input voltage in a single power stage. This inverter consists of two DC-DC bilateral boost converters in which work via time-variant duty cycles to produce sinusoidal voltage, and this feature causes complexity in control design. To deal with this complexity, new modeling so-called generalized averaged model is used to achieve a linear time-invariant model. In this paper, a nested control loop is designed. This control strategy consists of two control loops in which the inner loop is designed by linear quadratic regulator theory to displace poles in proper location and the second loop uses a PI-PR controller to track desired voltage and reject disturbances. To evaluate the proposed control method, the sliding mode controller is applied and compared as well. As shown by simulations, the proposed control strategy has more reliable performance and provides higher robustness in comparison with sliding mode control technique in rigid situations such as dealing with nonlinear load, parameters values changes, and external disturbances.
关键词： PI-PR,renewable energies,boost inverter,linear quadratic regulator,generalized averaged model
更新于2025-09-23 15:21:01
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Performance analysis of photovoltaic-thermal air collectors combined with a water to air heat exchanger for renewed air conditioning in building
摘要： In this work, a new solar system that includes photovoltaic-thermal (PVT) air collectors coupled to a water-to-air heat exchanger is investigated. The considered system generates sufficient energy for cooling and heating of the ambient air injected in a 300 m2 tertiary building and saves its total energy consumption. Therefore, it allows the minimization of greenhouse gas emissions of the building. A numerical model is developed to ensure comfortable temperatures during summer and winter, including days with the highest energy needs. The results show that the proposed system can generate the required heating and cooling needs using an airflow rate equal to 0.25 kg/s and a PVT area of 17 m2. It was found that the coupling of the PVT air collectors with a water to air heat exchanger minimizes the total required area for heating by ~ 33%. Moreover, the PV module’s efficiency was enhanced by 2.0% in winter and 5.1% in summer. The thermal energy saved for heating, thermal energy saved for cooling and the electrical energy saved are, respectively, equal to 15.30 kWh/day, 24.79 kWh/day, and 3.14 kWh/day. This represents an average emission reduction of 11.4 kg CO2 per day.
关键词： Water to air heat exchanger,Energy saving,Thermal comfort in buildings,Photovoltaic air collectors,Renewable energies,Greenhouse gas emissions
更新于2025-09-23 15:19:57
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Theoretical study of the structural and electronic properties of impurities in non-passivated silicon thin nanowires
摘要： In this work, we report theoretical results for the presence of the B, C, N, O and F as impurities in non-passivated [001] thin silicon nanowires. The results for the formation energies show that some dopants tend to segregate to the nanowire surfaces, as observed for passivated [110] ones, but at the double negative charge state. The most stable site for the considered impurities is the interstitial one, where the dopants make bridges with the lateral surface Si atoms, below to this surface, except for the oxygen and ?uorine ones, which stay close to the central Si atom. For the neutral carbon, nitrogen and ?uorine impurities, the surface π-states located at the facets are ?lled and a small bandgap appears in the calculated impurity band structures. However, if they were at the double negative charge state, the nanowire metallicity is recovered. Considering the boron and oxygen dopants, the neutral charge state enhances the metallic character at the opposite side of the nanowire where they are, which is reduced when two extra electrons are injected in the system and thus, opening slightly the nanowire bandgap. Our results clearly indicate that doping (or creating vacancies in) these nanowires with acceptors, as well as with hydrogen atoms, can reduce the thin nanowire metallic behavior.
关键词： Electronic structure,Silicon thin nanowires,First row impurities,DFT calculations,Formation energies
更新于2025-09-19 17:15:36
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Role of metallic dopants on the properties of copper (1) iodide nanopod-like structures
摘要： The addition of impurities as dopants to any material affects the properties of the material where the dopant modulates the optical and structural properties of the material. Copper (1) iodide films which were successfully doped with Al, Pb and Zn (as metallic dopants) were synthesized by the successive ionic layer adsorption and reaction (SILAR) technique while the morphological, structural, optical and electrochemical properties were investigated using the scanning electron microscope (SEM), X-ray diffraction (XRD), UV–Vis spectrophotometer and potentiostat respectively. The SEM image revealed a nanopod-like structure for the deposited CuI films while the XRD results confirmed the crystalline nature of the films with a face centered cubic structure. The optical results showed a progressive decrease of the absorbance values at increasing wavelengths while the optical bandgap energy of the undoped CuI film reduced from 2.47eV to 1.90eV, 1.75eV and 1.8eV for the Al-doped, Pb-doped and Zn-doped CuI films respectively. The undopedCuI film also showed a higher extinction coefficient value than the metallic-doped CuI films. The Zn-doped film had the maximum specific capacitance of 116 F g?1 at 2 mV/s.
关键词： Bandgap energies,Metallic dopants,CuI,SILAR,Specific capacitance
更新于2025-09-19 17:15:36
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Reduced-scaling approach for CIS and time-dependent DFT calculations using hybrid functionals
摘要： An approximation is presented which can efficiently decrease the computational expenses of configuration interaction singles (CIS) and time-dependent density functional theory (TDDFT) methods employing hybrid functionals. The approach is the adaptation of the local density fitting scheme developed for Hartree–Fock (HF) calculations for excited states and reduces the quartic scaling of the methods to cubic. It can also be applied to related methods, such as the time-dependent HF and Tamm–Dancoff approximation TDDFT approaches. Our benchmark calculations show that, for molecules of 50 to 100 atoms, average speedups of 2 to 4 can be achieved for CIS and TDDFT calculations at the expense of negligible errors in the calculated excitation energies and oscillator strengths, but for bigger systems or molecules of localized electronic structure significantly larger speedups can be gained. We also demonstrate that the approximation enables excited-state calculations on a single processor even for molecules of 1000 atoms using basis sets augmented with diffuse functions including more than 17000 atomic orbitals.
关键词： hybrid functionals,local density fitting,excitation energies,TDDFT,reduced scaling,CIS
更新于2025-09-19 17:15:36
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Hermitian second-order methods for excited electronic states: Unitary coupled cluster in comparison with algebraica??diagrammatic construction schemes
摘要： Employing an intermediate state representation (ISR) approach, Hermitian second-order methods for the calculation of electronic excitation energies are presented and compared in detail. These comprise the algebraic–diagrammatic construction scheme for the polarization propagator, a hybrid second-order ISR scheme based on traditional coupled-cluster theory as well as two similar approaches based on a unitary coupled-cluster (UCC) ansatz. Although in a strict perturbation-theoretical framework all prove to be identical, differences emerge when the corresponding converged cluster amplitudes are used and depending on how the similarity-transformed UCC Hamiltonian is evaluated. The resulting excitation energies, however, do not significantly differ for systems well described by means of perturbation theory.
关键词： unitary coupled-cluster,electronic excitation energies,intermediate state representation,perturbation theory,Hermitian second-order methods,algebraic–diagrammatic construction scheme
更新于2025-09-19 17:13:59