First-principles Calculations Research Articles

Computational study of the supramolecular complexation of azocompounds with cucurbit[7]uril: effects on the production and release of free radicals.

An inclusion complex between 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH), a widely employed azocompound, and cucurbit[7]util (CB[7]), has shown an increased yield of radicals derived from the homolytic cleavage of the azo bond. Aimed to get insights about the formation of complexes and their effect on the yield of radicals production, complexes of CB[7] with seven azocompounds were studied by computational methods. Molecular electrostatic surfaces and structural analysis showed that the inclusion of symmetrical azocompounds inside of CB[7] depends mainly on the charge density and position of the functional groups at the main chain of the azoderivative. Analysis of non-covalent interactions and thermodynamic outcomes revealed that positively charged azocompounds with amidinium or imidazolium groups presented strong favorable interactions (multiple hydrogen bonds) with the oxygens of CB[7] portals. Additionally, carbon-centered radicals generated from the complexes (azocompounds@CB[7]) were corroborated using the electron localization function (ELF). Results evidenced that the strength of the interactions and the level of inclusion (partial or complete) between the azocompound and CB[7] determined the final orientation of the radicals (located out- or inside of the CB[7] cavity). Obtained results could be employed to design new supramolecular systems based on the properties of azocomplound@CB[7] complexes for new scientific or industrial applications. First-principles calculations at B3LYP-D3BJ/6-311g(d,p) level theory in the gas phase and in solvent (PCM, water) were performed in Gaussian 16 software package. The dispersion energy correction was included through the Grimme's dispersion with Becke-Johnson damping D3(BJ). Thermodynamical data and the minimum character of all structures were obtained from vibrational frequency calculations. NBO, Multiwfn, Chemcraft, and NCIPLOT software were used to perform population analysis, analyze outcomes, visualize data, and display non-covalent interactions respectively.

Geometric optimisation and structural properties of organic−inorganic halide perovskites from van der Waals density functional theory calculations

Organic–inorganic hybrid perovskites have attracted extensive attention in the photovoltaic field due to their unique photoelectric properties and low production costs. Using the density functional theory-based first-principles calculations, we reported the geometric optimisation and structural properties of halide perovskites using van der Waals density functional theory calculations. The strongly constrained and appropriately normed (SCAN) meta-GGA with the revised Vydrov-van Voorhis no-local correlation functional (SCAN + rVV10) are promising van der Waals density functional for solving van der Waals (vdW) interaction problems that many non-empirical semilocal functionals fail to include. We found the optimised structure parameters of halide perovskites based on the SCAN + rVV10 functionals are much closer to the experimental results than other functional including PBE and PBE + vdW-TS functionals, which provides the fundamental aspect for the theoretical calculations of surfaces, interfaces, optical properties, and structure-properties relationship.

Language Model-Assisted Machine Learning, Photoelectrochemical, and First-Principles Investigation of Compatible Solvents for a CH3NH3PbI3 Film in Water.

Machine learning and data-driven methods have attracted a significant amount of attention for the acceleration of the design of molecules and materials. In this study, a material design protocol based on multimode modeling that combines literature modeling, numerical data collection, textual descriptor design, genetic modeling, experimental validation, first-principles calculation, and theoretical efficiency calculation is proposed, with a case study on designing compatible complex solvent molecules for a halide perovskite film, which is notorious for optoelectronic deactivation under hostile conditions, especially in water. In the multimode modeling design process, the textual descriptors play the central role and store rich literature scientific knowledge, which starts from the construction of a high-dimension literature model based on scientific articles and is realized by a genetic algorithm for materials predictions. The prediction is substantiated by follow-up experiments and first-principles calculations, leading to the successful identification of effective molecular combinations delivering an unprecedented large aqueous photocurrent (increasing by 3 orders of magnitude compared with that of CH3NH3PbI3) and remarkable aqueous stability (improving from 36% to 89% after immersion in water) under the hostile condition. This study provides a practical route via multimode modeling for accelerating the design of molecule-modified and solution-processed materials in a real scenario.

Interface modeling analysis using density functional theory in highly reliable Pt/HfO2/TaOx/Ta self-rectifying memristor

The self-rectifying memristor (SRM) is a promising device prototype for high-density three-dimensional (3D) integration and high-efficiency in-memory computing (IMC) by virtue of its ability to effectively suppress sneak current, simple device structure, and low energy consumption. Theoretically understanding the intrinsic mechanisms of SRM is a matter of concern. Here, we fabricated a Ta/TaOx/HfO2/Pt-stacked SRM exhibiting >103 on/off ratio, rectification ratio, and nonlinearity. The SRM can be repeatedly programmed by more than 106 pulses and demonstrates robust retention and high scalability (∼59 Mbit). A reasonable interface model for this SRM is established based on first-principles calculations. Using self-energy corrected density function theory, we calculate the barrier heights at each interface. Detailed I–V curve fitting and energy band analysis are performed and computationally verified to explain the intrinsic reasons for resistive switching, self-rectifying, and nonlinear behaviors. The work may advance the development of SRM prototype to enable energy-efficient 3D IMC.

Molecular insights into the performance of promoters for carbon dioxide hydrate

Hydrate-based CO2 storage is a cost-effective and environmentally friendly approach to reduce carbon emission, and the addition of hydrate promoters has shown a promising avenue for enhancing CO2 hydrate formation. In this work, the promotion mechanism and promotion performance of five different hydrate promoters (denoted as DIOX, CP, THF, THP, and CH) were investigated and compared by first-principles calculations and molecular dynamics simulations. The results show that the hydrate promoters prefer to singly occupy 51264 cages of the sII hydrate, and CO2 molecules can singly occupy 512 cage or multiply occupy 51264 cages. The cohesive energy density indicates that the optimum CO2 storage capacity can reach up to ∼28 wt%. The stabilization effects of hydrate promoters on the hydrate stability should follow the order of CP > CH > DIOX > THF ≈ THP. The hydrate promoters can increase the water-water interactions, and the molecular diffusivity shows that the dynamic stability of the hydrates is THP ≈ CH > CP > DIOX > THF. Further, the hydrate promoters can accelerate the hydrate formation kinetics, which reduce the induction time and increase the nucleation and growth process.

Fully spin-polarized two dimensional polar semi-metallic phase in Eu substituted GdI2 monolayer

Abstract The coexistence of seemingly mutually exclusive properties such as ferromagnetism, ferroelectricity and metallicity in atomically thin materials is the requirement of the hour in electronics as the Moore’s law faces an impending end. Only a few 2D multiferroic materials have been predicted/realized so far. The polar metals with simultaneous presence of polarity and conductivity are also equally rare. Here, we predict, based on first-principles calculations that an Eu-substituted rare-earth halide GdI2 monolayer showcases ferromagnetism, ferroelasticity while being polar and a fully spin-polarized semi-metal at the same time. The ferroelasticity and polarity are shown to be coupled making it possible to switch the polar direction using external mechanical stress. Further, it is observed that, an application of biaxial tensile strain of 5% causes the spin easy-axis to shift from out-of-plane to in-plane direction. Thus spin easy axis gets coupled with the direction of polarization in the strained monolayer making the switching of magnetization also possible using external strain. Simultaneous coexistence and coupling of the ferroic orders in a metallic 2D material makes the Eu substituted GdI2 monolayer an incredibly rare material for nano-electronics and spintronics applications.

Ferrimagnetic second-order topological insulator with valley polarization in two-dimensional magnet

Two-dimensional (2D) ferromagnetic and antiferromagnetic second-order topological insulators (SOTIs) coexisting with valley polarization have received increasing attention recently, while 2D valley-polarized ferrimagnetic (ferri-valley) SOTI has not been reported yet. In this work, we propose an effective six-band tight-binding model based on structural symmetry to confirm the possibility of coexistence of ferrimagnetism, second-order topological corner states, and valley polarization in 2D systems, and predict Mo2CSCl monolayer as the robust 2D ferri-valley SOTI with good structural stability, considerable Curie temperature estimated to be 100 K, and distinct valley polarization up to 109 meV under out-of-plane exchange field based on our model and first-principles calculations. Also, we find that the spin polarization direction of corner states combined with valley polarization can be controlled by switching the direction of the magnetization direction using an external magnetic field. These findings of the combination of intrinsic ferrimagnetism, second-order topological properties, and valley polarization in single 2D materials provide an ideal platform for practical applications in multifield-control spintronic devices.

Selective incorporation of antimony into gallium nitride

Dilute concentrations of antimony (Sb) incorporation into GaN induce strong bandgap bowing and tunable room-temperature photoluminescence from the UV to the green spectral regions. However, the atomistic details of the incorporation of Sb into the GaN host remain unclear. In this work, we use first-principles calculations to understand the thermodynamics of Sb substitution into GaN and its effect on the optical and Raman spectra. Although it is empirically considered that Sb is preferentially incorporated as an anion (Sb3−) into the N sublattice, we demonstrate that Sb can also be incorporated as a cation (Sb3+, Sb5+) into the metal sublattice. Our thermodynamic analysis demonstrates that SbN0, SbGa2+, and SbGa0 can co-exist under Ga-rich conditions in n-type samples. We further confirm the dual incorporation of Sb by calculating the vibrational frequencies of different anionic and cationic substitutions to explain the origins of experimentally observed additional Raman peaks of Sb-doped GaN. Moreover, the calculated band structures of different Sb substitutions into GaN explain the experimental photoluminescence and optical absorption spectra. Overall, our analysis suggests that the coexistence of Sb3−, Sb3+, and Sb5+ substitutions into GaN explains the totality of experimental measurements. Our results demonstrate that the selective incorporation of Sb into GaN (and potentially other group-V elements such as As, P, or Bi) by tuning the growth conditions can drastically modify the electronic properties, for applications in visible light emitters and photocatalysis.

Photocatalytic water splitting and charge carrier dynamics of Janus PtSSe/ζ-phosphorene heterostructure

On the basis of first-principles calculations and non-adiabatic molecular dynamics (NAMD) simulations, we explore the photocatalytic water splitting properties of PtSSe/ζ-Phosphorene heterostructure. This heterostructure possess semiconducting nature with high carrier mobility (≈ 103 cm2V− 1s− 1). The calculated high value of electron-hole recombination rate as compared to electron transfer rate and hole transfer rate, establish the Type-II mechanism more favorable for PtSSe/ζ-Phosphorene heterostructure. Further, the calculated value of solar-to-hydrogen (STH) conversion efficiency of PtSSe/ζ-Phosphorene exceeds to 10%, which makes it the potential candidate for commercial production of hydrogen for industrial use. STH conversion efficiency is further tunable on rotating one monolayer over other with specific angles in the heterostructure. Our study demonstrates PtSSe/ζ-Phosphorene heterostructure to be efficient Type II-scheme photocatalyst for water splitting.

Ideal quadratic nodal point in half-Heusler semimetal LaPtBi

The research focus on topological states in electronic systems has recently expanded from traditional linear dispersions to encompass higher-order dispersions. These higher-order dispersions exhibit unique physical properties, including high topological charge, exotic magnetoresponse, and novel transport behaviors. In this study, we employ first-principles calculations to propose the half-Heusler material LaPtBi as an ideal quadratic nodal point semimetal. Our comprehensive analysis of the band structure reveals an ideal nodal point located precisely at the Fermi level, exhibiting quadratic dispersion in all directions. This finding is supported by symmetry analysis and effective model arguments. Moreover, when the spin-orbit coupling effect is considered, the nodal point transitions from triple to quadruple degeneracy, while maintaining its quadratic dispersion. The material also features multiple prominent arc surface states originating from the nodal point, which are distinctly separated from the bulk bands. This separation facilitates experimental verification. Overall, LaPtBi, with its quadratic nodal point and advantageous properties, serves as an ideal platform for further research. The study of this material is expected to enhance our understanding of higher-order topological states in electronic systems, potentially driving future advancements in the field.

Above-room-temperature intrinsic ferromagnetism in ultrathin van der Waals crystal Fe3+xGaTe2

Two-dimensional (2D) van der Waals (vdW) magnets are crucial for ultra-compact spintronics. However, so far, no vdW crystal has exhibited tunable above-room-temperature intrinsic ferromagnetism in the 2D ultrathin regime. Here, we report the tunable above-room-temperature intrinsic ferromagnetism in ultrathin vdW crystal Fe3+xGaTe2 (x = 0 and 0.3). By increasing the Fe content, the Curie temperature (TC) and room-temperature saturation magnetization of bulk Fe3+xGaTe2 crystals are enhanced from 354 to 376 K and 43.9 to 50.4 emu·g−1, respectively. Remarkably, the robust anomalous Hall effect in 3-nm Fe3.3GaTe2 indicates a record-high TC of 340 K and a large room-temperature perpendicular magnetic anisotropy energy of 6.6 × 105 J m−3, superior to other ultrathin vdW ferromagnets. First-principles calculations reveal the asymmetric density of states and an additional large spin exchange interaction in ultrathin Fe3+xGaTe2 responsible for robust intrinsic ferromagnetism and higher TC. This work opens a window for above-room-temperature ultrathin 2D magnets in vdW-integrated spintronics.

A first-principles investigation into the adsorption behavior and deposition mechanism of boron-containing gases on Si(100) surfaces during chemical vapor deposition

Polysilicon serves as a primary raw material in the production of solar cells and semiconductors. However, its impurity content, particularly boron, poses significant challenges during the chemical vapor deposition (CVD) process. Therefore, it is essential to investigate the behavior of boron impurities during CVD. In this study, we conducted first-principles calculations to explore the adsorption behavior and deposition mechanism of boron-containing gases (BCl3, BHCl2, B2H6) on the Si(100) surface. We considered different adsorption sites and performed a systematic analysis of various adsorption systems' adsorption energy, charge transfer, and electronic properties. Our findings indicate that BCl3, BHCl2, and B2H6 molecules undergo dissociative chemisorption at specific adsorption sites. Moreover, charge transfer analysis confirms that each of these adsorbed molecules functions as an electron acceptor. Subsequent analyses, including total charge density (TCD), charge density difference (CDD), total density of states (TDOS), and projected density of states (PDOS), collectively underscore the robust electronic interactions between the gaseous molecules and the Si(100) surface. Through the computation of transition states and energy barriers across three potential reaction pathways, we identify a predominant sequence: BCl3→BCl2+Cl→BCl+Cl→B+Cl, that governs boron impurity formation on the Si(100) surface during CVD. Our work elucidates the underlying microscopic mechanisms of boron-containing gas adsorption and deposition in the CVD context.

Sliding-reversible bandgap modulation in irreversible asymmetric multilayers

The electronic bandgap of a material is often fixed after fabrication. The capability to realize on-demand and nonvolatile control over the bandgap will unlock exciting opportunities for adaptive devices with enhanced functionalities and efficiency. We introduce a general design principle for on-demand and nonvolatile control of bandgap values, which utilizes reversible sliding-induced polarization driven by an external electric field to modulate the irreversible background polarization in asymmetric two-dimensional (2D) multilayers. The structural asymmetry can be conveniently achieved in homobilayers of Janus monolayers and heterobilayers of nonpolar monolayers, making the design principle applicable to a broad range of 2D materials. We demonstrate the versatility of this design principle using experimentally synthesized Janus metal dichalcogenide multilayers as examples. Our first-principles calculations show that the bandgap modulation can reach up to 0.3 eV and even support a semimetal-to-semiconductor transition. By integrating a ferroelectric monolayer represented by 1T″′-MoS2 into a bilayer, we show that the combination of intrinsic ferroelectricity and sliding ferroelectricity leads to multi-bandgap systems coupled to multi-step polarization switching. The sliding-reversible bandgap modulation offers an avenue to dynamically adjust the optical, thermal, and electronic properties of 2D materials through mechanical and electrical stimuli.

Discovering novel γ-γ′ Pt-Al superalloys via lattice stability in Pt3Al induced by local atomic environment distortion

The strength of Pt-Al superalloys can be effectively improved using a coherent structure composed of a disordered γ phase and an ordered γ′ phase. However, γ′-Pt3Al has a cubic phase only at high temperatures and a tetragonal phase at low temperatures, thus breaking the coherent interface and deteriorating its mechanical properties. Here, high throughput first-principles calculations and rational experiments were conducted to discover novel γ-γ′ Pt-Al superalloys. The alloying strategy stabilizes the γ′ phase through the local charge distortion (LCD) or the local lattice distortion (LLD). Alloying elements, such as, Ti, Hf, and Ta, occupy the Al site in combination with Pt, making the spherical shape of change density in Pt3Al showing obvious directionality, i.e., LCD. Therefore, the stability of the γ′ phase is proposed at a lower alloying element concentration (3.125 at.%). However, alloying elements near Pt, e.g., Ni, Co, and Ru, tend to occupy the Pt site and induce LLD to stabilize the γ′ phase at higher alloying element concentration (12.5 at.%). The shape of the change density is similar to that of Pt3Al, and no obvious LCD is found when alloying elements occupy the Pt site. LCD-induced phase stability is observed exclusively at the Al site, whereas LLD-induced phase stability is solely present at the Pt site. The Pt-12Al-6X (X = Hf, Ti, Ta, Cr, and Ni in at.%) alloys were prepared, among which Pt-12Al-6Hf possessed a stable γ′ phase, a lower lattice misfit between γ and γ′, and a higher precipitation strengthening, resulting in its hardness (442.1 HV) surpassing that of Ni-based superalloys IN718 (413.6 HV). The γ′ phase in Pt-12Al-6Hf was characterized by high-resolution transmission electron microscopy, suggesting that the Pt site of the γ′ phase was occupied by Pt, while the Al site was shared by Pt, Al, and Hf. This is consistent with the calculated results.

Unconventional spin textures emerging from a universal symmetry theory of spin-momentum locking

Spin textures, i.e., the distribution of spin polarization vectors in reciprocal space, exhibit diverse patterns determined by symmetry constraints, resulting in a variety of spintronic phenomena. Here, we propose a universal theory to comprehensively describe the nature of spin textures by incorporating three symmetry flavors of reciprocal wavevector, atomic orbital, and atomic site. Such an approach enables us to establish a complete classification of spin textures constrained by the little co-group and predict some exotic spin texture types, such as Zeeman-type spin splitting in antiferromagnets and quadratic spin texture. To illustrate the influence of atomic orbitals and sites on spin textures, we predict orbital-dependent spin texture and anisotropic spin-momentum-site locking effects, and corresponding material candidates validated through first-principles calculations. The comprehensive classification and the predicted new spin textures in realistic materials are expected to trigger future spin-based functionalities in electronics.

The effects and mechanisms of two-dimensional V2C and V2CT2 (T = O, F, and OH) on hydrogen adsorption and dissociation properties of MgH2: First-principles calculations

Two-dimensional vanadium carbide (V2C) MXene has been confirmed the excellent catalytic activity on hydrogen storage of magnesium hydride (MgH2) in experimental. In present work, adsorption energy, density of states (DOS), charge density difference, dissociation barrier and dehydrogenation energy of the small MgH2 clusters on V2C and V2CT2 (T = O, F, and OH) were investigated by using density functional theory (DFT). The results revealed that the (MgH2)1 cluster adsorbed on the V2C has the best adsorption energy with −0.91eV and the lengths of Mg–H bonds were increased from 1.71 Å to 1.77 Å. The electronic structure results displayed that the H s states hybridized with the V d states, and the charge transferred from H atoms to V atoms. In addition, the (MgH2)1 cluster could be spontaneously dissociated on the V2C, and the dissociation barriers of (MgH2)2 and (MgH2)4 clusters on the V2C reduced by 1.33 and 1.25 eV than that of pristine (MgH2)2 and (MgH2)4 clusters, respectively. Compared with the pristine (MgH2)4 cluster, the dehydrogenation energies of (MgH2)4 cluster were dramatically promoted by adding V2C. The thermodynamic performance of MgH2 were noticeably improved.

The design of Mg–Ti–V–Nb–Cr lightweight high entropy alloys for hydrogen storage

In this study, body-centered-cubic Ti24V18Nb6Cr12 high entropy alloy (HEA) is selected as the matrix to design Mg–Ti–V–Nb–Cr lightweight HEAs. Based on first-principles calculations, the hydrogen storage properties of a series of Mg–Ti–V–Nb–Cr HEAs are systematically investigated. The designed Mg-based HEAs are found to be stable after hydrogenation and exhibit high gravimetric hydrogen storage capacities (HSCs). Particularly, the gravimetric HSC of Mg6Ti24V18Cr12 HEA is as high as 4.091 wt%. Besides, the dehydrogenation temperature of the Mg–Ti–V–Nb–Cr HEAs decreases obviously with increasing Mg content, which results from the weakened bonding strength of <M-H> pairs. This study demonstrates that the Mg6Ti24V18Cr12 HEA is a potential candidate for hydrogen storage.

Sliding Ferroelectricity Induced Ultrafast Switchable Photovoltaic Response in ε-InSe Layers.

2D sliding ferroelectric semiconductors have greatly expanded the ferroelectrics family with the flexibility of bandgap and material properties, which hold great promise for ultrathin device applications that combine ferroelectrics with optoelectronics. Besides the induced different resistance states for non-volatile memories, the switchable ferroelectric polarizations can also modulate the photogenerated carriers for potentially ultrafast optoelectronic devices. Here, it is demonstrated that the room temperature sliding ferroelectricity can be used for ultrafast switchable photovoltaic response in ε-InSe layers. By first-principles calculations and experimental characterizations, it is revealed that the ferroelectricity with out-of-plane (OOP) polarization only exists in even layer ε-InSe. The ferroelectricity is also demonstrated in ε-InSe-based vertical devices, which exhibit high on-off ratios (≈104) and non-volatile storage capabilities. Moreover, the OOP ferroelectricity enables an ultrafast (≈3ps) bulk photovoltaic response in the near-infrared band, rendering it a promising material for self-powered reconfigurable and ultrafast photodetector. This work reveals the essential role of ferroelectric polarization on the photogenerated carrier dynamics and paves the way for hybrid multifunctional ferroelectric and optoelectronic devices.

Theoretical study of HfS2 as anode material of zinc ion battery in sports wearable equipment

In this study, the density functional theory (DFT) based on first-principles calculations was used to conduct a comprehensive theoretical calculation of the Zn adsorption HfS2 system (Zn-HfS2) to develop the potential of HfS2 as an anode material for zinc ion batteries (ZIBs). The calculation results show that the adsorption energy decreases gradually (−1.368 eV) with the increase of shear deformation. There is a significant charge transfer from Zn to HfS2 monolayer, and the electrons of Zn atoms flow to S atoms. The intrinsic HfS2 shows a band gap value of 2.055 eV, and Zn-HfS2 shows a metal property with a zero band gap. The adsorption of Zn leads to an increase in energy near the Fermi level, indicating that the adsorption of Zn enhances the electronic conductivity of HfS2. The deformation reduces the barrier of Zn in the diffusion path to 0.16 eV. The maximum specific capacity of HfS2 to Zn is 447.445 mAh/g. The calculation results will help promote the application of zinc ion batteries in wearable devices.

Comparative investigation of structural, electronic, mechanical and optical responses of CsPbI3-PbSe and CsPbI3 with Mg-doped for optoelectronic applications: A first-principles study

A and B-site doping has been viewed as a very effective approach to stabilise the desired perovskite cube phase of pure and doped hetero-structure CsPbI3-Pb1-xMgxSe and the simple system CsPb1-xMgxI3. In this analysis, the effect of (Mg2+) on the crystal structure, electronic, mechanical, and optical responses of hetero-structure CsPbI3-Pb1-xMgxSe and CsPb1-xMgxI3 were thoroughly investigated, by employing first-principles computations. A theoretical study of target responses of the metal-halide CsPbI3 is presented with a plane wave ultra-soft pseudopotential approach as personified in the CASTP code. The computed results show that the band gap of CsPbI3-Pb1-xMgxSe can be changed from '1.809eV' to '1.75eV' when the concentration range (x = 0 to 0.25) is changed. A valuable band gap of '0.48eV' and '1.28eV' of doped CsPbI3-Pb1-xMgxSe can be achieved under concentrations changed from (x = 0.25 to '0.75eV') and as shown in direct (Γ - Γ) nature and become optically active. The density of states shows that Cs-6p, I-4p, and Pb-6p states contribute to the valence band maximum, whereas the main involvement conduction band minimum by Mg-5p and Cs-6p states in the CsPbI3-Pb1-xMgxSe system. Elastic properties designate the flexibility and softness of target materials. The computed elastic parameters further indicate that this hetero-structure material is stable under the doping concentration condition. Replacing the Pb2+ site with Mg2+ has red-shifted the maximum absorption edges and changed the optical characteristics to be anisotropic. Their ability of these two materials with their Mg2+ based mixed halide perovskite nature for optoelectronic applications.