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This talk introduced our research on developing sensing materials for harsh environmental applications. By combining first-principles density functional theory simulations with AI/ML approach, we have established a sensor database which can predict candidate materials at given operating conditions.
Large momentum effective theory (LaMET) provides a general framework for computing the multi-dimensional partonic structure of the proton from first principles using lattice quantum chromodynamics (QCD). In this effective field theory approach, LaMET predicts parton distributions through a power expansion and perturbative matching of a class of Euclidean observables—quasi-distributions—evaluated at large proton momenta. Recent advances in lattice renormalization, such as the hybrid scheme with leading renormalon resummation, together with improved matching kernel that incorporates higher-loop corrections and resummations, have enhanced both the perturbative and power accuracy of LaMET, enabling a reliable quantification of theoretical uncertainties. Moreover, the Coulomb-gauge correlator approach further simplifies lattice analyses and improves the precision of transverse-momentum-dependent structures, particularly in the non-perturbative region. State-of-the-art LaMET calculations have already yielded certain parton observables with important phenomenological impact. In addition, the recently proposed kinematically enhanced lattice interpolation operators promise access to unprecedented proton momenta with greatly improved signal-to-noise ratios, which will extend the range of LaMET prediction and further suppress the power corrections. The remaining challenges, such as controlling excited-state contamination in lattice matrix elements and extracting gluonic distributions, are expected to benefit from emerging lattice techniques for ground-state isolation and noise reduction. Thus, lattice QCD studies of parton physics have entered an exciting stage of precision control and systematic improvement, which will have a broader impact for nuclear and particle experiments.
It was recently estimated that the strong isospin-symmetry breaking (ISB) corrections to the Fermi matrix element in free neutron decay could be of the order 10 –4 , one order of magnitude larger than the naïve estimate based on the Behrends-Sirlin-Ademollo-Gatto theorem. To investigate this claim, we derive a general expression of the leading ISB correction to hadronic Fermi matrix elements, which takes the form of a four-point correlation function in lattice gauge theory and is straightforward to compute from first principles. Our formalism paves the way for the first determination of such correction in the neutron sector with fully-controlled theory uncertainties.
The structural, electronic, and magnetic properties of adsorbed SiC monolayer with a series of nonmagnetic metal atoms, including Al, Ga, Li, Mg, and Na, are systematically investigated using first-principles calculations. Magnetic behavior shows in the Al-, Ga-, Li-, and Na-adsorbed systems, and both nonmagnetic metals and their neighboring Si/C atoms contribute to the magnetism. Meanwhile, due the most stable structure of Al-adsorbed SiC monolayer, we investigated the magnetic interaction between two Al atoms. A long-range antiferromagnetic (AFM) is always observed as the Al-Al distance increases. Our results show that the two-Al-adsorbed 2D SiC exhibits an AFM order due to the p-p hybridization mechanism.
The large non-saturating magnetoresistance (MR) of bulk WTe 2 is known to be greatly reduced in thin films with decreasing thickness. In this study, based on first-principles calculations, we demonstrate that 2D WTe 2 bonded to graphene, through a WTe 2 /graphene van der Waals (vdW) heterojunction, can exhibit a significantly enhanced MR, which can be even larger than that of bulk WTe 2 . Moreover, the MR shows a strong stacking-orientation-dependent behavior, which facilitates a tunable MR effect. We report our findings illustrate a new route to enhancing the MR of WTe 2 and other 2D semimetals via heterojunction engineering, which is useful for a range of applications in information technology.
Composed of inexpensive and naturally abundant elements, the chalcopyrite mineral CuFeS 2 has received attention as a potentially useful thermoelectric. We use first-principles electronic structure and Boltzmann transport theory calculations to investigate thermoelectric properties of n -doped CuFeS 2 . We find that energy-dependent carrier lifetimes that are inversely proportional to the electronic density-of-states are crucial for reproducing experimental data on the transport properties, including the measured values of the Seebeck coefficient, α. The heavy-effective-mass conduction band promotes high values of α, but it also leads to low mobility due to strong electron-acoustic-phonon scattering. Low mobility forces one to rely on high carrier concentration to achieve high conductivity, which decreases α and limits the achievable power factor. Our calculations predict that ideally doped CuFeS 2 that has been nanostructured to an average grain size d≈20nm can attain thermoelectric figures of merit z T=0.25 to 0.8 for T=300 to 700 K, respectively, due to a reduction in the lattice thermal conductivity.
Intersystem crossing is a common and important nonadiabatic process in molecular systems. Revealed with a first-principles investigation, the quenching of C( 1 D) by N 2 is efficient due to multiple passages via long-lived collisional resonances, despite relatively small spin–orbit couplings.
Ever since ferroelectricity was discovered in HfO2, the question of its origin remains controversial. Here, we probe this question using a combination of Landau theory of phase transitions and first-principles computations. In such an approach, the energy landscape associated with the phase transition between cubic and different experimentally demonstrated phases of HfO2 (tetragonal, monoclinic, orthorhombic Pbca, orthorhombic Pnma, and orthorhombic Pca21) is explored using density functional theory calculations. Computations revealed that stabilization of all but orthorhombic Pbca phase is driven by a single unstable zone-boundary antipolar mode X2−. When coupled with zone-center modes (Γ1+ and Γ3+), it stabilizes the tetragonal phase. Coupling with four additional modes (Γ5+, X3−, X5−, X5+) results in the monoclinic phase, which is the ground state of the material. If, however, Γ5+ mode is replaced with Γ4− mode, orthorhombic polar phase Pca21 is stabilized. The application of this framework to examine the effect of electric field on the ferroelectric phase of hafnia reveals that the field of 5 MV/cm is capable of stabilizing ferroelectric phase over the monoclinic one at 0 K.
Gallium nitride (GaN) is a key semiconductor for solid-state lighting, but its radiative processes are not fully understood. Here we show a first-principles approach to accurately compute the radiative lifetimes in bulk uniaxial crystals, focusing on wurtzite GaN. Our computed radiative lifetimes are in very good agreement with experiment up to 100 K. We show that taking into account excitons (through the Bethe–Salpeter equation) and spin–orbit coupling is essential for computing accurate radiative lifetimes. A model for exciton dissociation into free carriers allows us to compute the radiative lifetimes up to room temperature. Our work enables precise radiative lifetime calculations in III-nitrides and other anisotropic solid-state emitters.
We study the electronic and magnetic structures of quasi-one-dimensional interfaces along the zigzag direction in two-dimensional GaN/SiC heterostructures using first-principles calculations. Four representative heterostructures with six inequivalent interfaces are discussed in detail. Our results indicate that a bulk electric field will develop only when both interfaces feature no gap states and the total net charge at interfaces are of opposite sign. All the geometries studied exhibit an intriguing quasi-one-dimensional conductor character, of which three show finite nonzero magnetic moment. Furthermore, the magnetic moment in one of the systems can be tuned by applying an electric field along the normal direction of monolayer indicating a strong magnetoelectric coupling. Our analysis shows that the magnetization at the interfaces is closely related to the density of states at the Fermi level due to the Stoner instability, and the ribbon-width-dependent magnetization for different geometries implies the existence of an in-bulk electric field.
Twelve layered hybrid organic-inorganic perovskites combining oligoacene derivatives [phenylmethylammonium (PMA), naphthylmethylammonium (NMA), anthrylmethylammonium (AMA), and tetrylmethylammonium (TMA)] and lead halides (Cl - , Br - , and I - anions) are investigated by first-principles density functional theory (DFT), showing broad, rational tunability of band gap, quantum well type, and spin-dependent energy band properties. Six compounds are known from previous syntheses and are used to devise a computational search space for likely low-energy structures. Among the six known compounds, a refined structure is identified for (NMA) 2 PbCl 4 and a new, lower-energy structure is suggested for (AMA) 2 PbCl 4 . The DFT based search methodology is next applied to predict the likely structures for the six unknown compounds. Computationally predicted energy levels for all 12 compounds from spin-orbit coupled hybrid DFT reveal tunable type I quantum well alignments, with frontier orbitals located on the inorganic component, on the organic component, or on both, as controlled by cation and anion selection. In conclusion, several structures spontaneously break local and global inversion symmetry, causing strong spin splitting of the conduction bands [up to 0.12 eV for (PMA) 2 PbCl 4 ] and showing potential for spin-dependent transport properties and future spintronic and tunable chiroptical applications.
One of the key challenges in separation science is the lack of precise ion separation methods and mechanistic understanding crucial for efficiently recovering critical materials from complex aqueous matrices. Herein, first-principles electronic structure calculations and in situ Raman spectroscopy are studied to elucidate the factors governing ion discrimination in an adsorptive membrane specifically designed for transition metal ion separation. Density functional theory calculations and in situ Raman data jointly reveal the thermodynamically favorable binding preferences and detailed adsorption mechanisms for competing ions. How membrane binding preferences correlate with the electronic properties of ligands is explored, such as orbital hybridization and electron localization. The findings underscore the importance of the phenolate group in oxime ligands for achieving high selectivity among competing transition metal ions. In-depth understanding on which specific atomistic site within the microenvironment of metal-ligand binding pockets governs the ion discrimination behaviors of the host will build a solid foundation to guide the rational design of next-generation materials for precision separation essential for energy technologies and environment remediation. In tandem, synthetic controllability is demonstrated to transform 3D micrometer-scale crystals to a 2D crystalline selective layer in membranes, paving the way for more precise and sustainable advances in separation science.
The structural, electronic, and magnetic properties of monolayer boron nitride (BN) doped with a series of nonmagnetic metal atoms, including Ga, Li, Mg, and Na, are systematically investigated by the first-principles method. Both different dopants and doping sites are considered. Magnetic behavior is observed in the systems doped with Li, Mg, and Na atoms. On the other hand, owing to the stable structures of the BN monolayers with Li and Mg dopants among the three magnetic systems, we study the magnetic interaction in these two systems. Interestingly, a long-range ferromagnetic (FM) coupling is observed in the BN monolayer with two Li atoms doped as the Li–Li distance increases. Our results show that the FM interaction originates from a p–d exchange-like s–p coupling interaction. Moreover, nonmagnetic state appears in the system with two Mg dopants.
The structural, electronic, and magnetic properties of binary Heusler alloys ZCl{sub 3} (Z = Li, Na, K, Rb) with DO{sub 3}-type structure have been studied by means of the first principle calculations. The calculated results reveal that all four alloys are half-metallic (HM) materials at the stable ferromagnetic ground state. The total magnetic moments (M{sub t}) of LiCl{sub 3}, NaCl{sub 3}, KCl{sub 3,} and RbCl{sub 3} alloys are all 2.000 μ{sub B}/f.u., following the Slater-Pauling rule M{sub t} = 24 − Z{sub t} for the former two alloys, while satisfying the Slater-Pauling rule M{sub t} = 30 − Z{sub t} for the latter two alloys. The spin-up band gaps of the binary Heusler alloys ZCl{sub 3} (Z = Li, Na, K, Rb) are 5.598, 5.687, 6.744, and 6.745 eV at equilibrium lattice constants 7.076, 7.237, 7.588, and 7.819 Å, respectively. The positive cohesion energy and negative formation energy indicate that they are thermodynamically stable. Moreover, wide HM regions for binary Heusler alloys ZCl{sub 3} (Z = Li, Na, K, Rb) show their HM characters are robust when the lattices are expanded or compressed under uniform and tetragonal strains. Finally, the total charge density, magnetic charge density, and charge density difference of the (110) plane for LiCl{sub 3} alloy are analyzed in detail.
Although perovskite oxyhydrides (POHs) have shown promise as a support for selective hydrogenation, it is unknown if they themselves can catalyze alkyne semi-hydrogenation. Here, we use first-principles density functional theory, coupled with microkinetic modeling, to investigate acetylene semi-hydrogenation on a prototypical POH, cubic BaTiO 2.5 H 0.5 (BTOH). Two different mechanisms are examined on a representative surface of BTOH under the reaction conditions: both are based on the Horiuti–Polanyi mechanism, but the way of H 2 dissociation is different. In mechanism 1, a lattice hydride H atom and then a surface adsorbed H atom sequentially hydrogenate the adsorbed acetylene. In mechanism 2, two lattice hydride H atoms from the BTOH sequentially hydrogenate the adsorbed acetylene. In both mechanisms, the H atoms are replenished from gas phase H 2 dissociation. Using density functional theory (DFT), we have calculated pathways for these two mechanisms in hydrogenation of acetylene to ethylene, as well as further to ethane. Microkinetic modeling based on the DFT energetics indicates that at 523 K, hydrogenation to ethylene and ethane via mechanism 1 occurs at a rate up to two orders of magnitude faster than via mechanism 2. A selectivity analysis for the temperature range of 373–673 K shows that the product observed is essentially only ethylene within the more active mechanism 1. This is because at the steady state, there is a significant amount of surface anion vacancies that facilitate heterolytic H 2 dissociation and help stabilize a vinyl intermediate. In conclusion, the present findings suggest that POHs are capable of selective hydrogenation, thanks to their rich hydrogen surface-redox chemistry.
Abstract The electronic transport behaviour of materials determines their suitability for technological applications. We develop a computationally efficient method for calculating carrier scattering rates of solid-state semiconductors and insulators from first principles inputs. The present method extends existing polar and non-polar electron-phonon coupling, ionized impurity, and piezoelectric scattering mechanisms formulated for isotropic band structures to support highly anisotropic materials. We test the formalism by calculating the electronic transport properties of 23 semiconductors, including the large 48 atom CH 3 NH 3 PbI 3 hybrid perovskite, and comparing the results against experimental measurements and more detailed scattering simulations. The Spearman rank coefficient of mobility against experiment ( r s = 0.93) improves significantly on results obtained using a constant relaxation time approximation ( r s = 0.52). We find our approach offers similar accuracy to state-of-the art methods at approximately 1/500th the computational cost, thus enabling its use in high-throughput computational workflows for the accurate screening of carrier mobilities, lifetimes, and thermoelectric power.
Instanton rate theory is used to study tunneling events in a wide range of systems including low-temperature chemical reactions. Despite many successful applications, the method has never been obtained from first principles, relying instead on the “Im F” premise. In this paper, the same expression for the rate of barrier penetration at finite temperature is rederived from quantum scattering theory [W. H. Miller, S. D. Schwartz, and J. W. Tromp, J. Chem. Phys. 79, 4889 (1983)] using a semiclassical Green’s function formalism. This justifies the instanton approach and provides a route to deriving the rate of other processes.
We calculated the partial charges in methylammonium (MA) lead-iodide perovskite CH{sub 3}NH{sub 3}PbI{sub 3} in its different crystalline phases using different first-principles electronic charge partitioning approaches, including the Bader, ChelpG, and density-derived electrostatic and chemical (DDEC) schemes. Among the three charge partitioning methods, the DDEC approach provides chemically intuitive and reliable atomic charges for this material, which consists of a mixture of transition metals, halide ions, and organic molecules. The DDEC charges are also found to be robust against the use of hybrid functionals and/or upon inclusion of spin–orbit coupling or dispersive interactions. We calculated explicitly the atomic charges with a special focus on the dipole moment of the MA molecules within the perovskite structure. The value of the dipole moment of the MA is reduced with respect to the isolated molecule due to charge redistribution involving the inorganic cage. DDEC charges and dipole moment of the organic part remain nearly unchanged upon its rotation within the octahedral cavities. Our findings will be of both fundamental and practical importance, as the accurate and consistent determination of the atomic charges is important in order to understand the average equilibrium distribution of the electrons and to help in the development of force fields for larger scale atomistic simulations to describe static, dynamic, and thermodynamic properties of the material.