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1.
Nanomaterials (Basel) ; 11(12)2021 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-34947746

RESUMO

The model of a graphene (Gr) sheet putting on a silicon (Si) substrate is used to simulate the structures of Si microparticles wrapped up in a graphene cage, which may be the anode of lithium-ion batteries (LIBS) to improve the high-volume expansion of Si anode materials. The common low-energy defective graphene (d-Gr) structures of DV5-8-5, DV555-777 and SV are studied and compared with perfect graphene (p-Gr). First-principles calculations are performed to confirm the stable structures before and after Li penetrating through the Gr sheet or graphene/Si-substrate (Gr/Si) slab. The climbing image nudged elastic band (CI-NEB) method is performed to evaluate the diffusion barrier and seek the saddle point. The calculation results reveal that the d-Gr greatly reduces the energy barriers for Li diffusion in Gr or Gr/Si. The energy stability, structural configuration, bond length between the atoms and layer distances of these structures are also discussed in detail.

2.
J Phys Condens Matter ; 34(7)2021 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-34753113

RESUMO

Zr-Rh metallic glass has enabled its many applications in vehicle parts, sports equipment and so on due to its outstanding performance in mechanical property, but the knowledge of the microstructure determining the superb mechanical property remains yet insufficient. Here, we develop a deep neural network potential of Zr-Rh system by using machine learning, which breaks the dilemma between the accuracy and efficiency in molecular dynamics simulations, and greatly improves the simulation scale in both space and time. The results show that the structural features obtained from the neural network method are in good agreement with the cases inab initiomolecular dynamics simulations. Furthermore, we build a large model of 5400 atoms to explore the influences of simulated size and cooling rate on the melt-quenching process of Zr77Rh23. Our study lays a foundation for exploring the complex structures in amorphous Zr77Rh23, which is of great significance for the design and practical application.

3.
Small ; 17(39): e2102699, 2021 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-34396696

RESUMO

g-C3 N4 /CdS heterojunctions are potential photocatalysts for hydrogen production but their traditional type-II configuration generally leads to weak oxidative and reductive activity. How to construct the novel Z-scheme g-C3 N4 /CdS counterparts to address this issue remains a great challenge in this field. In this work, a new direct Z-scheme heterojunction of defective g-C3 N4 /CdS is designed by introducing cyano groups (NC-) as the active bridge sites. Experimental observations in combination with density functional theory (DFT) calculations reveal that the unique electron-withdrawing feature of cyano groups in the defective g-C3 N4 /CdS heterostructure can endow this photocatalyst with numerous advantageous properties including high light absorption ability, strong redox performance, satisfactory charge separation efficiency, and long lifetime of charge carriers. Consequently, the resultant photocatalytic system exhibits more active performance than CdS and g-C3 N4 under visible light and reaches an excellent hydrogen evolution rate of 1809.07 µmol h-1 g-1 , which is 6.09 times higher than pristine g-C3 N4 . Moreover, the defective g-C3 N4 /CdS photocatalyst maintains good stability after 40 h continuous test. This work provides new insights into design and construction of Z-scheme heterojunctions for regulating the visible-light-induced photocatalytic activity for H2 evolution.

4.
Dalton Trans ; 50(19): 6463-6476, 2021 May 18.
Artigo em Inglês | MEDLINE | ID: mdl-34002748

RESUMO

Complex polymorphic relationships in the LnSiP3 (Ln = La and Ce) family of compounds are reported. An innovative synthetic method was developed to overcome differences in the reactivities of the rare-earth metal and refractory silicon with phosphorus. Reactions of atomically mixed Ln + Si with P allowed for selective control over the reaction outcomes resulting in targeted isolation of three new polymorphs of LaSiP3 and two polymorphs of CeSiP3. In situ X-ray diffraction studies revealed that the developed method bypasses formation of the thermodynamic dead-end, the binary SiP. Careful re-determination of the crystal structure ruled out the previously reported ordered centrosymmetric structure of CeSiP3 and showed that the main LnSiP3 polymorphs crystallize in the non-centrosymmetric Pna21 and Aea2 space groups featuring distinct distortions of the regular P square net to yield either cis-trans 1D phosphorus chains (Pna21) or disordered-2D phosphorus layers (Aea2). The disordered 2D nature of the P layers in the Aea2 LaSiP3 polymorph was confirmed by Raman spectroscopy. A unique centrosymmetric P21/c polymorph was observed for LaSiP3 and has a completely different crystal structure lacking P layers. Consecutive polymorphic transformations at increasing temperatures for LaSiP3(Pna21 → P21/c → Aea2) were derived from optimized synthetic profiles and confirmed by a combination of phonon computations and experimental in situ and ex situ annealings. Crystal structures of the LaSiP3 polymorphs were verified via advanced solid state NMR analysis using 31P MAS and 31P{139La} double resonance techniques. A combination of phonon and electronic structure calculations, NMR T1 relaxation times, UV/Vis/NIR spectroscopy, and resistivity measurements revealed that all the reported polymorphs are semiconductors with resistivities and thermal conductivities strongly dependent on the degree of distortion of P square layers in the crystal structure. Reported here, non-centrosymmetric LnSiP3 polymorphs with tunable resistivity and thermal conductivity provide a platform for the development of novel functional materials with a wide range of applications.

5.
J Am Chem Soc ; 143(11): 4213-4223, 2021 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-33719436

RESUMO

The pursuit of two-dimensional (2D) borides, MBenes, has proven to be challenging, not the least because of the lack of a suitable precursor prone to the deintercalation. Here, we studied room-temperature topochemical deintercalation of lithium from the layered polymorphs of the LiNiB compound with a considerable amount of Li stored in between [NiB] layers (33 at. % Li). Deintercalation of Li leads to novel metastable borides (Li∼0.5NiB) with unique crystal structures. Partial removal of Li is accomplished by exposing the parent phases to air, water, or dilute HCl under ambient conditions. Scanning transmission electron microscopy and solid-state 7Li and 11B NMR spectroscopy, combined with X-ray pair distribution function (PDF) analysis and DFT calculations, were utilized to elucidate the novel structures of Li∼0.5NiB and the mechanism of Li-deintercalation. We have shown that the deintercalation of Li proceeds via a "zip-lock" mechanism, leading to the condensation of single [NiB] layers into double or triple layers bound via covalent bonds, resulting in structural fragments with Li[NiB]2 and Li[NiB]3 compositions. The crystal structure of Li∼0.5NiB is best described as an intergrowth of the ordered single [NiB], double [NiB]2, or triple [NiB]3 layers alternating with single Li layers; this explains its structural complexity. The formation of double or triple [NiB] layers induces a change in the magnetic behavior from temperature-independent paramagnets in the parent LiNiB compounds to the spin-glassiness in the deintercalated Li∼0.5NiB counterparts. LiNiB compounds showcase the potential to access a plethora of unique materials, including 2D MBenes (NiB).

7.
Nanoscale ; 13(3): 1485-1506, 2021 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-33439199

RESUMO

Encapsulation of metal nanoparticles just below the surface of a prototypical layered material, graphite, is a recently discovered phenomenon. These encapsulation architectures have potential for tuning the properties of two-dimensional or layered materials, and additional applications might exploit the properties of the encapsulated metal nanoclusters themselves. The encapsulation process produces novel surface nanostructures and can be achieved for a variety of metals. Given that these studies of near-surface intercalation are in their infancy, these systems provide a rich area for future studies. This Review presents the current progress on the encapsulation, including experimental strategies and characterization, as well as theoretical understanding which leads to the development of predictive capability. The Review closes with future opportunities where further understanding of the encapsulation is desired to exploit its applications.

8.
Phys Rev Lett ; 125(19): 195503, 2020 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-33216596

RESUMO

We report the laser-induced solid-state transformation between a periodic "approximant" and quasicrystal in the Al-Cr system during rapid quenching. Dynamic transmission electron microscopy allows us to capture in situ the dendritic growth of the metastable quasicrystals. The formation of dendrites during solid-state transformation is a rare phenomenon, which we attribute to the structural similarity between the two intermetallics. Through ab initio molecular dynamics simulations, we identify the dominant structural motif to be a 13-atom icosahedral cluster transcending the phases of matter.

9.
Artigo em Inglês | MEDLINE | ID: mdl-33017810

RESUMO

An appropriate treatment of electronic correlation effects plays an important role in accurate descriptions of physical and chemical properties of real materials. The recently proposed Correlation Matrix Renormalization theory with Sum Rule correction (CMR) for studying correlated electron materails has shown good performance in molecular systems and a periodic Hydrogen chain in comparison with various quantum chemistry and quantum Monte Carlo calculations. This work gives a detailed formulation and computational code implementation of CMR in multi-band periodic lattice systems. This lattice CMR ab initio theory is highly efficient, has no material specific adjustable parameters, and has no double counting issues faced by the hybrid approaches like LDA+U, DFT+DMFT and DFT+GA type theories. Benchmark studies on materials with s and p orbitals in this study show that CMR in its current implementation consistently performs well for these systems as the electron correlation increases from the bonding region to the bond breaking region.

10.
J Chem Theory Comput ; 16(10): 6256-6266, 2020 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-32877181

RESUMO

We develop a resource-efficient step-merged quantum imaginary time evolution approach (smQITE) to solve for the ground state of a Hamiltonian on quantum computers. This heuristic method features a fixed shallow quantum circuit depth along the state evolution path. We use this algorithm to determine the binding energy curves of a set of molecules, including H2, H4, H6, LiH, HF, H2O, and BeH2, and find highly accurate results. The required quantum resources of smQITE calculations can be further reduced by adopting the circuit form of the variational quantum eigensolver (VQE) technique, such as the unitary coupled cluster ansatz. We demonstrate that smQITE achieves a similar computational accuracy as VQE at the same fixed-circuit ansatz, without requiring a generally complicated high-dimensional nonconvex optimization. Finally, smQITE calculations are carried out on Rigetti quantum processing units, demonstrating that the approach is readily applicable on current noisy intermediate-scale quantum devices.

11.
Phys Chem Chem Phys ; 22(25): 13975-13980, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32609127

RESUMO

Due to the high cost and insufficient resources of lithium, alternative sodium-ion batteries have been widely investigated for large-scale applications. NaFePO4 has the highest theoretical capacity of 154 mA h g-1 among the iron-based phosphates, which makes it an attractive cathode material for Na-ion batteries. Experimentally, LiFePO4 has been highly successful as a cathode material in Li-ion batteries because its olivine crystal structure provides a stable framework during battery cycling. In NaFePO4, maricite replaces olivine as the most stable phase. However, the maricite phase is experimentally found to be electrochemically inactive under normal battery operating voltages (0-4.5 V). We found that partial substitutions of Na with Li stabilize the olivine structure and may be a way to improve the performance of NaFePO4 cathodes. Using the previously developed structural LiFePO4 database, we examined the low-energy crystal structures in the system when we replace Li with Na. The known maricite and olivine NaFePO4 phases are reconfirmed and an unreported phase with energy between them is identified by our calculations. Besides, the Li-doped olivine type compound LixNa1-xFePO4 with mixed alkali ions retains better energetic stability compared with the other two types of structures of the same composition, as long as the proportion of Li exceeds 0.25. The thermodynamic stability of o-type LixNa1-xFePO4 can be further improved at finite temperatures. The primary limitation of the calculations is that we mainly focus on the zero-temperature condition; however, the relative stability of the structures may vary depending on the ambient temperature.

12.
ChemSusChem ; 13(18): 4985-4993, 2020 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-32671990

RESUMO

Z-scheme photocatalytic systems are an ideal band alignment structure for photocatalysis because of the high separation efficiency of photo-induced carriers while simultaneously preserving the strong reduction activity of electrons and oxidation activity of holes. However, the design and construction of Z-scheme photocatalysts is challenging because of the need for appropriate energy band alignment and built-in electric field. Here, we propose a novel approach to a Z-scheme photocatalytic system using density functional theory calculations with the HSE06 hybrid functional. The undesirable type-I g-C3 N4 /MoSe2 heterojunction is transformed into a direct Z-scheme system through boron doping of g-C3 N4 (B-doped C3 N4 /MoSe2 ). Detailed analysis of the total and partial density of states, work functions and differential charge density distribution of the B-doped C3 N4 /MoSe2 heterojunction shows the proper band alignment and existence of a built-in electric field at the interface, with the direction from g-C3 N4 to MoSe2 , demonstrating a direct Z-scheme heterojunction. Further investigation on the absorption spectra reveals a large enhancement of the light absorption efficiency after boron doping. The results consistently confirm that electronic structures and photocatalytic performance can be effectively manipulated by a facile boron doping. Modulating the band alignment of heterojunctions in this way provides valuable insights for the rational design of highly efficient heterojunction-based photocatalytic systems.

13.
ACS Nano ; 14(6): 6795-6802, 2020 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-32479719

RESUMO

A first-principles prediction of the binary nanoparticle phase diagram assembled by solvent evaporation has eluded theoretical approaches. In this paper, we show that a binary system interacting through the Lennard-Jones (LJ) potential contains all experimental phases in which nanoparticles are effectively described as quasi hard spheres. We report a phase diagram consisting of 53 equilibrium phases, whose stability is quite insensitive to the microscopic details of the potentials, thus giving rise to some type of universality. Furthermore, we show that binary lattices may be understood as consisting of certain particle clusters, i.e., motifs, that provide a generalization of the four conventional Frank-Kasper polyhedral units. Our results show that metastable phases share the very same motifs as equilibrium phases. We discuss the connection with packing models, phase diagrams with repulsive potentials, and the prediction of likely experimental superlattices.

14.
Phys Chem Chem Phys ; 22(17): 9759-9766, 2020 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-32334427

RESUMO

Phase-change materials such as Ge-Sb-Te compounds have attracted much attention due to their potential value in electrical data storage. In contrast to the amorphous and crystalline phases, supercooled liquids are far from being deeply understood despite their inevitable role in both amorphization and crystallization processes. To this end, we have studied the dynamics properties and structural characteristics of liquid and supercooled liquid Ge3Sb2Te6 during the fast cooling process. As the temperature decreases, chemical bonds become more homogeneous, but coordination numbers of Ge, Sb and Te atoms change very little. Meanwhile, the structural order of short-range configuration is obviously enhanced. Further studies suggest that Ge-centered, Sb-centered and Te-centered configurations change to the more ordered defective octahedrons mainly by adjusting the bond-angle relationship and bond length, rather than just by changing the coordination environment. It is the more ordered octahedrons that promote the formation of medium-range order. Our findings provide a deep insight into the origin of local structural order in supercooled liquid Ge3Sb2Te6, which is of great importance for the comprehensive understanding of amorphization and crystallization processes.

15.
Nat Commun ; 11(1): 1348, 2020 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-32165638

RESUMO

Employing high-rate ion-intercalation electrodes represents a feasible way to mitigate the inherent trade-off between energy density and power density for electrochemical energy storage devices, but efficient approaches to boost the charge-storage kinetics of electrodes are still needed. Here, we demonstrate a water-incorporation strategy to expand the interlayer gap of α-MoO3, in which water molecules take the place of lattice oxygen of α-MoO3. Accordingly, the modified α-MoO3 electrode exhibits theoretical-value-close specific capacity (963 C g-1 at 0.1 mV s-1), greatly improved rate capability (from 4.4% to 40.2% at 100 mV s-1) and boosted cycling stability (from 21 to 71% over 600 cycles). A fast-kinetics dual-ion-intercalation energy storage device is further assembled by combining the modified α-MoO3 anode with an anion-intercalation graphite cathode, operating well over a wide discharge rate range. Our study sheds light on a promising design strategy of layered materials for high-kinetics charge storage.

16.
Phys Rev Lett ; 123(10): 105701, 2019 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-31573294

RESUMO

Relaxation processes significantly influence the properties of glass materials. However, understanding their specific origins is difficult; even more challenging is to forecast them theoretically. In this study, using microseconds molecular dynamics simulations together with an accurate many-body interaction potential, we predict that an Al_{90}Sm_{10} metallic glass would have complex relaxation behaviors: In addition to the main (α) relaxation, the glass (i) shows a pronounced secondary (ß) relaxation at cryogenic temperatures and (ii) exhibits an anomalous relaxation process (α_{2}) accompanying α relaxation. Both of the predictions are verified by experiments. Computational simulations reveal the microscopic origins of relaxation processes: while the pronounced ß relaxation is attributed to the abundance of stringlike cooperative atomic rearrangements, the anomalous α_{2} process is found to correlate with the decoupling of the faster motions of Al with slower Sm atoms. The combination of simulations and experiments represents a first glimpse of what may become a predictive routine and integral step for glass physics.

17.
Angew Chem Int Ed Engl ; 58(44): 15855-15862, 2019 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-31373096

RESUMO

Two novel lithium nickel boride polymorphs, RT-LiNiB and HT-LiNiB, with layered crystal structures are reported. This family of compounds was theoretically predicted by using the adaptive genetic algorithm (AGA) and subsequently synthesized by a hydride route with LiH as the lithium source. Unique among the known ternary transition-metal borides, the LiNiB structures feature Li layers alternating with nearly planar [NiB] layers composed of Ni hexagonal rings with a B-B pair at the center. A comprehensive study using a combination of single crystal/synchrotron powder X-ray diffraction, solid-state 7 Li and 11 B NMR spectroscopy, scanning transmission electron microscopy, quantum-chemical calculations, and magnetism has shed light on the intrinsic features of these polymorphic compounds. The unique layered structures of LiNiB compounds make them ultimate precursors for exfoliation studies, thus paving a way toward two-dimensional transition-metal borides, MBenes.

18.
J Phys Condens Matter ; 31(33): 335601, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31067512

RESUMO

We propose an approach that is under the framework of Gutzwiller wave function but goes beyond the commonly adopted Gutzwiller approximation to improve the accuracy and flexibility in treating the correlation effects. Detailed formalism is described for a dimer which is straightforwardly generalized later to more complicated periodic bulk systems. The accuracy of the approach is demonstrated by evaluating the potential energy curves of spin-singlet N2 dimer, spin-triplet O2 dimer, and 1D hydrogen chain. The computational workload of the approach can be easily handled by efficient parallel computing.

19.
ACS Appl Mater Interfaces ; 11(22): 19986-19993, 2019 Jun 05.
Artigo em Inglês | MEDLINE | ID: mdl-31083896

RESUMO

For lithium-sulfur batteries (LSBs), the dissolution of lithium polysulfide and the consequent "shuttle effect" remain major obstacles for their practical applications. In this study, we designed a new cathode material comprising MoSe2/graphene to selectively adsorb polysulfides on the selenium edges and thus to mitigate their dissolution. More specifically, few-layered MoSe2 was first grown on nitrogen-doped reduced graphene oxide (N-rGO) using the chemical vapor deposition method and then infiltrated with sulfur as the cathode for LSBs. An initial capacity of 1028 mA h g-1 was achieved for S/MoSe2/N-rGO at 0.2 C, higher than 981 and 405.1 mA h g-1 for pure graphene and sulfur, respectively, along with enhanced cycling durability and rate capability. Moreover, the density functional theory simulation, in addition to the experimental adsorption test, X-ray photoelectron spectroscopy analysis, and transmission electron microscopy technique, reveals the dual roles that MoSe2 plays in improving the performance of LSBs by functioning as the binding sites for lithium polysulfides and as the platform that enables fast Li-ion diffusion by reducing its diffusion barrier. The reported finding suggests that the transition-metal selenides could be an efficient alternative material as the cathode for LSBs.

20.
J Phys Condens Matter ; 31(19): 195902, 2019 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-30736027

RESUMO

We report benchmark calculations of the correlation matrix renormalization (CMR) approach for 23 molecules in the well-established G2 molecule set. This subset represents molecules with spin-singlet ground state in a variety of chemical bonding and coordination environments. The QUAsi-atomic minimal basis-set orbitals (QUAMBOs) are used as local orbitals in both CMR and full configuration interaction (FCI) calculations for comparison. The results obtained from the calculations are also compared with available experimental data. It is shown that the CMR method produces binding and dissociation energy curves in good agreement with the QUAMBO-FCI calculations as well as experimental results. The CMR benchmark calculations yield a standard deviation of 0.09 Å for the equilibrium bond length and 0.018 Hartree/atom for the formation energy, with a gain of great computational efficiency which scales like Hartree-Fock method.

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