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Revealing the Spectrum of Unknown Layered Materials with Super-Human Predictive Abilities
摘要： We discover the chemical composition of over 1000 materials that are likely to exhibit layered and two-dimensional phases but have yet to be synthesized. This includes two materials our calculations indicate can exist in distinct structures with different band gaps, expanding the short list of two-dimensional phase change materials. While databases of over 1000 layered materials have been reported, we provide the first full database of materials that are likely layered but yet to be synthesized, providing a roadmap for the synthesis community. We accomplish this by combining physics with machine learning on experimentally obtained data and verify a subset of candidates using density functional theory. We find our model performs five times better than practitioners in the field at identifying layered materials and is comparable or better than professional solid-state chemists. Finally, we find that semi-supervised learning can offer benefits for materials design where labels for some of the materials are unknown.
关键词： two-dimensional materials,machine learning,materials discovery,density functional theory,layered materials
更新于2025-09-09 09:28:46
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surface alloy
摘要： We have investigated the atomic and electronic structure of the (√3×√3)R30? SnAu2/Au(111) surface alloy. Low-energy electron diffraction and scanning tunneling microscopy measurements show that the native herringbone reconstruction of bare Au(111) surface remains intact after formation of a long-range ordered (√3×√3)R30? SnAu2/Au(111) surface alloy. Angle-resolved photoemission and two-photon photoemission spectroscopy techniques reveal Rashba-type spin-split bands in the occupied valence band with comparable momentum space splitting as observed for the Au(111) surface state, but with a hole-like parabolic dispersion. Our experimental findings are compared with density functional theory (DFT) calculation that fully support our experimental findings. Taking advantage of the good agreement between our DFT calculations and the experimental results, we are able to extract that the occupied Sn-Au hybrid band is of (s, d )-orbital character, while the unoccupied Sn-Au hybrid bands are of (p, d )-orbital character. Hence we can conclude that the Rashba-type spin splitting of the hole-like Sn-Au hybrid surface state is caused by the significant mixing of Au d with Sn s states in conjunction with the strong atomic spin-orbit coupling of Au, i.e., of the substrate.
关键词： angle-resolved photoemission spectroscopy,density functional theory,SnAu2/Au(111) surface alloy,Rashba-type spin splitting,two-photon photoemission spectroscopy
更新于2025-09-09 09:28:46
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with pentagonal structure
摘要： Structure-property relationships have always been guiding principles for materials discovery. Here we explore the relationships to discover two-dimensional (2D) materials with the goal of identifying 2D magnetic semiconductors for spintronics applications. In particular, we report a density functional theory + U study of single-layer antiferromagnetic (AFM) semiconductor CoS2 with the pentagonal structure forming the so-called Cairo tessellation. We ?nd that this single-layer magnet exhibits an indirect band gap of 1.06 eV with electron and hole effective masses of 0.52 and 1.93 m0, respectively, which may lead to relatively high electron mobility. The hybrid density functional theory calculations correct the band gap to 2.24 eV. We also compute the magnetocrystalline anisotropy energy (MAE), showing that the easy axis of the AFM ordering is along the b axis with a sizable MAE of 153 μeV per Co ion. We further calculate the magnon frequencies at different spin-spiral vectors, based on which we estimate the N′eel temperatures to be 20.4 and 13.3 K using the mean ?eld and random phase approximations, respectively. We then apply biaxial strains to tune the band gap of single-layer pentagonal CoS2. We ?nd that the energy difference between the ferromagnetic and AFM structures strongly depends on the biaxial strain, but the ground state remains the AFM ordering. Although the low critical temperature prohibits the magnetic applications of single-layer pentagonal CoS2 at room temperature, the excellent electrical properties may ?nd single-layer semiconductor applications in optoelectronic nanodevices.
关键词： two-dimensional materials,magnon frequencies,N′eel temperature,biaxial strain,Cairo tessellation,antiferromagnetic semiconductor,density functional theory,band gap,magnetocrystalline anisotropy energy,pentagonal structure,spintronics
更新于2025-09-09 09:28:46
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Size and strain effects on mechanical and electronic properties of green phosphorene nanoribbons
摘要： Recently, a phosphorus isomer named green phosphorus was theoretically predicted with a similar interlayer interaction compared to that of black phosphorus, thus indicating that individual layers can be mechanically exfoliated to form two-dimensional (2D) layers known as green phosphorene. In this work, we investigated the properties of green phosphorene nanoribbons along both armchair and zigzag directions with ribbon widths up to 57 ? using density functional theory. Effects of ribbon width and strain on the mechanical and electronic properties of the ribbons were studied. The Young’s modulus, effect of quantum con?nement on the band gap, and effect of strain on the band structures of the ribbons were investigated. The green phosphorene ribbons were found to exhibit prominent anisotropic properties, with the Young’s modulus in the range of 10-35 GPa for the armchair green phosphorene nanoribbons (AGPNR) and 160-170 GPa for the zigzag green phosphorene nanoribbons (ZGPNR), which are the same order of magnitude as those of the 2D sheets. The work function was found to be between 5 eV ～ 5.7 eV for the range of widths studied. Both size and strain trigger direct-indirect band gap transitions in the ribbons and their transition mechanisms were discussed.
关键词： green phosphorene,mechanical properties,nanoribbons,electronic properties,density functional theory
更新于2025-09-09 09:28:46
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Quantum behavior of hydrogen-vacancy complexes in diamond
摘要： Hydrogen plays an essential role in the growth process of artificial diamond and can easily form complexes with lattice vacancies. Despite substantial efforts to resolve the electronic structure and the ground-state properties of the hydrogen-vacancy (HV) center, the final remarks are ambiguous, while the complexes of vacancy with two and more hydrogen atoms remain unexplored. In this paper, we used spin-polarized, hybrid density-functional theory method to investigate electronic structure and magneto-optical properties of various hydrogen-vacancy clusters in diamond. Our theoretical results indicate a very strong tendency toward the formation of HnV complexes up to four hydrogen atoms that are mostly electrically and optically active centers. One of the investigated defects introduce highly correlated electronic states that pose a challenge for density-functional theory and, therefore, require special treatment when charge- and spin-density-related properties are determined. We introduced an extended Hubbard model Hamiltonian with fully ab initio provided parameters to analyze the complex electronic structure of highly correlated H2V0 defects. The role of quantum tunneling of hydrogen in HV center and its impact on the hyperfine structure was discussed. We demonstrate that experimentally observed HV1? center is similar to well-known NV1?, i.e., I) it possesses triplet 3A ground state and 3E excited state in C3v symmetry; II) the calculated zero-phonon line is 1.71 eV (1.945 eV for NV1?). A detailed experimental reinvestigation based on optically detected electron paramagnetic resonance spectroscopy is suggested to verify whether the HV1? center has metastable singlet shelving states between the ground and excited state triplets and, as a result, whether it may exhibit a spin-selective decay to the ground state.
关键词： quantum tunneling,diamond,hydrogen-vacancy complexes,magneto-optical properties,density-functional theory,quantum behavior
更新于2025-09-09 09:28:46
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Electronic states of dibenzo-p–dioxin. A synchrotron radiation linear dichroism Investigation
摘要： The UV absorbance bands of dibenzo-p-dioxin (dibenzo-1,4-dioxin, DD) are investigated by synchrotron radiation linear dichroism (SRLD) spectroscopy on molecular samples aligned in stretched polyethylene. The investigation covers the range 58000–30000 cm–1 (170–330 nm), thereby providing new information on the transitions of DD in the vacuum UV region. The observed polarization data enable experimental symmetry assignments of the observed transitions, leading to revision of previously published assignments by Ljubi? and Sablji? (J. Phys. Chem. A 109 (2005) 8209-8217). In general, the experimental spectra are well predicted by the results of quantum chemical calculations using time-dependent density functional theory (TD–DFT). The observed absorbance in the region 58000–55000 cm–1 (170–180 nm) in the vacuum UV is almost entirely short-axis polarized, in pleasing agreement with the predicted spectrum.
关键词： Dibenzo-p-dioxin,Near and vacuum UV,Stretched polyethylene,Polarization directions,Time-dependent density functional theory (TD-DFT),Synchrotron radiation,Linear dichroism (LD)
更新于2025-09-09 09:28:46
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Surface enhanced Raman spectroscopy with methyl-orange on Ag-TiO2 nanocomposites: Experimental and theoretical investigation
摘要： Ag-TiO2 nanocomposites of different Ag nanoparticle (NP) concentrations are experimentally prepared and their UV-vis and surface enhanced Raman scattering characteristics are determined. The enhancement of the Raman signal for the ligand methyl-orange (MO) adsorbed onto the nanocomposite system, is observed. To investigate the influence of changing Ag concentration in this nanocomposite system, molecular dynamics (MD) simulations are conducted with both a fixed as well as varying number of the surfactant MO adsorbed onto the nanocomposite. Density functional theory (DFT) simulations are performed to investigate the conditions for charge transfer from the MO surfactant via the highest occupied molecular orbitals (HOMO), lowest unoccupied molecular orbitals (LUMO) as well as the electrostatic potentials. It is shown that the bonding mode of the surfactant contributes greatly to the observed Raman scattering enhancement.
关键词： HOMO-LUMO,Surface Enhanced Raman Scattering,density functional theory,molecular dynamics,Ag-TiO2 nanocomposite,electrostatic potential
更新于2025-09-09 09:28:46
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Chemical inactivity of GaN(0001) surface – The role of oxygen adsorption – Ab initio picture
摘要： Density Functional Theory (DFT) calculations were used to determine adsorption of oxygen at GaN(0001), i.e. Ga-terminated surface. It was shown that at low coverage the oxygen molecule dissociates during adsorption so that the two separate O adatoms are located in H3 sites. Oxygen adatom saturates three Ga broken bonds, modifying their energy by overlap with Op states, so that the three states are degenerate with valence band (VB). The electron counting rule (ECR) indicate on the electron surplus, the excess electrons are donated to other Ga broken bond states, the adsorption energy is equal to 3.74 eV/atom for clean surface. At the first critical coverage it is, the Fermi level is shifted to conduction band while at the second critical coverage shifted down to VBM. The adsorption energy is for, for and decreases and, respectively, for the energy jumps to, and for higher coverage the energy rapidly decreases to zero and becomes negative The singular point at is essential for stability of oxygen coverage of the surface. The equilibrium pressure at low coverage is 10?5 bar for 1500 K and 10?12 bar 1000 K. It is reduced for higher coverage, due to reduction of the energy and configurational entropy contributions. At the coverage the pressure is reduced by several orders of magnitude, indicating extremely high thermodynamic stability of such coverage, which is responsible for chemical inactivity of GaN(0001) surface observed in experiments, the critical factor for mechano-chemical polishing of the substrates for electronic applications.
关键词： Density functional theory,Surface,Oxygen,Gallium nitride
更新于2025-09-09 09:28:46
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Probing the upper band gap of atomic rhenium disulfide layers
摘要： Here, we investigate the ultrafast carrier dynamics and electronic states of exfoliated ReS2 films using time-resolved second harmonic generation (TSHG) microscopy and density functional theory (DFT) calculations. The second harmonic generation (SHG) of layers with various thicknesses is probed using a 1.19-eV beam. Up to ~13 nm, a gradual increment is observed, followed by a decrease caused by bulk interferometric light absorption. The addition of a pump pulse tuned to the exciton band gap (1.57 eV) creates a decay-to-rise TSHG profile as a function of the probe delay. The power and thickness dependencies indicate that the electron–hole recombination is mediated by defects and surfaces. The two photon absorptions of 2.38 eV in the excited state that are induced by pumping from 1.57 to 1.72 eV are restricted because these transitions highly correlate with the forbidden d–d intrasubshell orbital transitions. However, the combined usage of a frequency-doubled pump (2.38 eV) with wavelength-variant SHG probes (2.60–2.82 eV) allows us to vividly monitor the variations in TSHG profiles from decay-to-rise to rise-to-decay, which imply the existence of an additional electron absorption state (s-orbital) at an approximate distance of 5.05 eV from the highest occupied molecular orbital states. This observation was critically examined by considering the allowance of each electronic transition and a small upper band gap (~0.5 eV) using modified DFT calculations.
关键词： density functional theory,ReS2,time-resolved spectroscopy,ultrafast carrier dynamics,second harmonic generation
更新于2025-09-09 09:28:46
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Performance of DFT for C <sub/>60</sub> Isomerization Energies: A Noticeable Exception to Jacob’s Ladder
摘要： The ability to accurately calculate relative energies of fullerenes is important in many areas of computational nanotechnology. Due to the large size of fullerenes, their relative energies cannot normally be calculated by means of high-level ab initio procedures, and therefore density functional theory (DFT) represents a cost-effective alternative. In an extensive benchmark study, we calculate the electronic energies of eight C60 isomers by means of the high-level G4(MP2) composite procedure. G4(MP2) isomerization energies span a wide range between 307.5–1074.0 kJ mol–1. We use this benchmark data to assess the performance of DFT, double-hybrid DFT (DHDFT), and MP2-based ab initio methods. Surprisingly, functionals from the second and third rungs of Jacob’s Ladder (i.e., GGA and meta-GGA functionals) significantly and systematically outperform hybrid and hybrid-meta-GGA functionals, which occupy higher rungs of Jacob’s Ladder. In addition, DHDFT functionals do not offer a substantial improvement over meta-GGA functionals, with respect to isomerization energies. Overall, the best performing functionals with mean absolute deviations (MADs) below 15.0 kJ mol–1 are (MADs given in parenthesis) the GGA N12 (14.7); meta-GGAs M06-L (10.6), M11-L (10.8), MN15-L (11.9), and TPSS-D3BJ (12.8); and the DHDFT functionals B2T-PLYP (9.3), mPW2-PLYP (9.8), B2K-PLYP (12.1), and B2GP-PLYP (12.3 kJ mol–1). In light of these results, we recommend the use of meta-GGA functionals for the calculation of fullerene isomerization energies. Finally, we show that inclusion of very small percentages of exact Hartree–Fock exchange (3–5%) slightly improves the performance of the GGA and meta-GGA functionals. However, their performance rapidly deteriorates with the inclusion of larger percentages of exact Hartree–Fock exchange.
关键词： Buckminsterfullerene,coupled cluster theory,G4(MP2) theory,density functional theory
更新于2025-09-04 15:30:14