First-principles Approach Research Articles

Systematic strain-induced bandgap tuning in binary III–V semiconductors from density functional theory

The modification of the nature and size of bandgaps for III-V semiconductors is of strong interest for optoelectronic applications. Strain can be used to systematically tune the bandgap over a wide range of values and induce indirect-to-direct transition (IDT), direct-to-indirect transition (DIT), and other changes in bandgap nature. Here, we establish a predictive first-principles approach, based on density functional theory, to analyze the effect of uniaxial, biaxial, and isotropic strain on the bandgap. We show that systematic variation is possible. For GaAs, DITs are observed at 1.56% isotropic compressive strain and 3.52% biaxial tensile strain, while for GaP an IDT is found at 2.63% isotropic tensile strain. We additionally propose a strategy for the realization of direct-to-indirect transition by combining biaxial strain with uniaxial strain. Further transition points are identified for strained GaSb, InP, InAs, and InSb and compared to the elemental semiconductor silicon. Our analyses thus provide a systematic and predictive approach to strain-induced bandgap tuning in binary III-V semiconductors.

Theoretical study of Schottky regulation of graphene/MoSe2 heterojunctions by non-metal doping

The Schottky regulation mechanism of nonmetal-doped graphene/MoSe2 heterojunctions was investigated using a first-principles approach. Graphene and MoSe2 bonded with weak van der Waals forces to form a stable structure. The combination of graphene and MoSe2 still maintains their respective intrinsic properties and forms an n-type Schottky contact. Non-metal doping can effectively modulate the Schottky type and height of graphene/MoSe2 heterojunctions. B and P doping of MoSe2 transforms MoSe2 from a direct band-gap semiconductor to metal, and when combined with graphene to form a heterojunction, the heterojunction behaves as an ohmic contact.After N-doped MoSe2 combines with graphene to form a heterojunction, the Schottky type is converted from n-type to p-type. The doping of C and Si atoms reduces the direct band gap of MoSe2, and the doping of S increases the band gap of MoSe2 but does not have much effect on it. When C-, Si- and S-doped MoSe2 is combined with graphene to form a heterojunction, impurity energy levels appear in the conduction band and effectively reduce the band gap of MoSe2, resulting in a lower Schottky barrier.

Separating weak integrated information theory into inspired and aspirational approaches.

Mediano etal. (The strength of weak integrated information theory. Trends Cogn Sci 2022;26: 646-55.) separate out strong and weak flavours of the integrated information theory (IIT) of consciousness. They describe 'strong IIT' as attempting to derive a universal formula for consciousness and 'weak IIT' as searching for empirically measurable correlates of aspects of consciousness. We put forward that their overall notion of 'weak IIT' may be too weak. Rather, it should be separated out to distinguish 'aspirational-IIT', which aims to empirically test IIT by making trade-offs to its proposed measures, and 'IIT-inspired' approaches, which adopt high-level ideas of IIT while dropping the mathematical framework it reaches through its introspective, first-principles approach to consciousness.

Effect of substitutional oxygen on the cohesion of transition-metal nitride multilayers

Using a first-principles approach, we investigated the effect of oxygen as a substitutional impurity on cohesion of three transition metal nitride multilayers. Namely, we studied AlN/VN, AlN/TiN, and VN/TiN systems in a rock salt structure (B1) with (001) interfaces. The preferred oxygen positions were determined with the help of calculations of free energy that also included contribution from the vibrational entropy. Subsequent calculations of the cleavage energy for all possible cleavage planes enabled us to identify the weakest link and assess the impact of the oxygen impurity on a cohesion of each of the studied multilayers. Supercells of different sizes were used to estimate the effect of oxygen concentration. Our results indicate that oxygen prefers to replace nitrogen atoms in interfacial planes and that these impurities do not reduce the multilayer cohesion. Moreover, in the case of the AlN/TiN system, their presence was found to increase cohesion of the interface.

Investigations of thermoelectric properties of different gallium nitride polytypes through first-principles approach

In recent years, exploring new polytypes of III-V semiconductors has been widely practiced for the development of thermoelectric devices of high efficiency. In this work, the thermoelectric properties of new polytypes, namely the wurtzite(wz), Berrylium oxide (β-BeO), Nickel arsenide (NiAs), Silicon carbide (SiC), and Titanium arsenide (TiAs) phases of GaN have been investigated using the first-principles approaches. It is found that the p-type of doping induces enhancement of the power factors (PFs) and figure-of-merits (zT) of the GaN polytypes. The optimal p-type doping for PFs has been recognized as −1.67 eV for wz-GaN, −1.78 eV for β-BeO-GaN, −1.33 eV for NiAs-GaN, −1.58 eV for SiC-GaN, and −1.48 eV for TiAs-GaN. These optimal p-type doping has induced the room-temperature PFs as high as 13.75 × 1010 W/mK2s recorded for wz-GaN, 13.61 × 1010 W/mK2s for β-BeO-GaN, 41.14 × 1010 W/mK2s for NiAs-GaN, 14.06 × 1010 W/mK2s for SiC-GaN, and 49.21 × 1010 W/mK2s for TiAs-GaN. Furthermore, the PFs of the GaN polytypes are enhanced by increasing the temperature. Due to such significant PFs, the zT values corresponding to p-type doping have been recorded as 1.013 for wz-GaN, 0.998 for β-BeO-GaN, 1.00 for NiAs-GaN, 1.015 for SiC-GaN, and 0.999 for TiAs-GaN. Moreover, we comprehensively discussed the electrical and thermal conductivities and Seebeck coefficients (S) for the predicted GaN polytypes. The results of the thermoelectric properties presented in this study reveal the predicted GaN polytypes may find interesting applications in thermoelectric devices for clean energy harvesting.

Bateson's Process Ontology for Psychological Practice

AbstractThe work of Gregory Bateson offers a metaphysical basis for a “process psychology,” that is, a view of psychological practice and research guided by an ontology of becoming—identifying change, difference, and relationship as the basic elements of a foundational metaphysics. This article explores the relevance of Bateson's recursive epistemology, his reconception of the Great Chain of Being, a first-principles approach to defining the nature of mind, and understandings of interaction and difference, pattern and symmetry, interpretation and context. Bateson's philosophical contributions will be drawn into relationship with Wittgenstein's philosophy of language as use, Melnyk's theory of causal levels of explanation, Korzybski's account of map and territory, the rejection of the heuristic rigidity of substantialist ontologies, and a cybernetics communication science-informed approach to contextual-bidirectionality of causality. We thereby arrive at an understanding of Bateson's process psychology that, given its ecological-systemic nature, is explanatorily applicable across the mind sciences. This process psychology equips us to answer the question: What is mind? Not by explanatory appeal to substantial entities contained within mind, but instead by recourse to the contextually relevant patterns for understanding mind to a particular purpose. We have thereby attended to the gulf between heuristics and fundamentals, between psychological models and an onto-epistemic account of reality. Insufficient attention has been given to characterizing the vital nature of Bateson's philosophical oeuvre to psychological practice. This article draws out Bateson's relevance to establishing foundational principles for a process psychology capable of reinvigorating psychological thought.

Exciton Lifetime and Optical Line Width Profile via Exciton-Phonon Interactions: Theory and First-Principles Calculations for Monolayer MoS2.

Exciton dynamics dictates the evolution of photoexcited carriers in photovoltaic and optoelectronic devices. However, interpreting their experimental signatures is a challenging theoretical problem due to the presence of both electron-phonon and many-electron interactions. We develop and apply here a first-principles approach to exciton dynamics resulting from exciton-phonon coupling in monolayer MoS2 and reveal the highly selective nature of exciton-phonon coupling due to the internal spin structure of excitons, which leads to a surprisingly long lifetime of the lowest-energy bright A exciton. Moreover, we show that optical absorption processes rigorously require a second-order perturbation theory approach, with photon and phonon treated on an equal footing, as proposed by Toyozawa and Hopfield. Such a treatment, thus far neglected in first-principles studies, gives rise to off-diagonal exciton-phonon self-energy, which is critical for the description of dephasing mechanisms and yields exciton line widths in excellent agreement with experiment.

First-principle study on the lattice-directed missing linker defect in zirconium based metal-organic framework (MOF-801): Electronic properties and interaction with hydrogen

The nature of defects in metal-organic frameworks (MOFs) due to missing linker has been studied using first-principle approach based on periodic density functional theory (DFT). MOF-801 as zirconium-based MOFs is investigated in this study due to its densely packed structure where a zirconium node is coordinated with twelve fumarate ligands. In this study, the missing linker defect was formed by removing fumarate ligand in each lattice direction and the energy is compared. The removal of one fumarate ligand in each lattice direction seems to have relatively homogenous energy distribution with small energy differences when the defect sites are capped with formate HCOO- (FA), chloride (Cl-), hydroxide (OH-) ions, OH- plus H2O and Cl- plus H2O according to the HSE06 calculations. The electronic properties of defective MOF-801 have shown that removing a fumarate ligand decreases the bandgap energy by small fraction which can be further identified from the density of states. The application of defective MOF-801 was also tested for hydrogen adsorption. The adsorption energy indicates that the presence of defect might increase the affinity of MOF-801 for hydrogen storage in certain binding sites. This study shows further understanding about the nature of defect due to missing linker in densely packed MOF-801 and its prospect for hydrogen storage.

Hadronic light-by-light scattering contribution to the muon g − 2 from lattice QCD: semi-analytical calculation of the QED kernel

Hadronic light-by-light scattering is one of the virtual processes that causes the gyromagnetic factor g of the muon to deviate from the value of two predicted by Dirac’s theory. This process makes one of the largest contributions to the uncertainty of the Standard Model prediction for the muon (g − 2). Lattice QCD allows for a first-principles approach to computing this non-perturbative effect. In order to avoid power-law finite-size artifacts generated by virtual photons in lattice simulations, we follow a coordinate-space approach involving a weighted integral over the vertices of the QCD four-point function of the electromagnetic current carried by the quarks. Here we present in detail the semi-analytical calculation of the QED part of the amplitude, employing position-space perturbation theory in continuous, infinite four-dimensional Euclidean space. We also provide some useful information about a computer code for the numerical implementation of our approach that has been made public at https://github.com/RJHudspith/KQED.

Effects of fission product doping on the structure, electronic structure, mechanical and thermodynamic properties of uranium monocarbide: A first-principles study

A first-principle approach within the framework of density functional theory was employed to study the effect of vacancy defects and fission products (FPs) doping on the mechanical, electronic, and thermodynamic properties of uranium monocarbide (UC). Firstly, the calculated vacancy formation energies confirm that the C vacancy is more stable than the U vacancy. The solution energies indicate that FPs prefer to occupying in U site rather than in C site. Zr, Mo, Th, and Pu atoms tend to directly replace U atom and dissolve into the UC lattice. Besides, the results of the mechanical properties show that U vacancy reduces the compressive and deformation resistance of UC while C vacancy has little effect. The doping of all FPs except He has a repairing effect on the mechanical properties of U1-xC. In addition, significant modifications are observed in the phonon dispersion curves and partial phonon density of states (PhDOS) of UC1-x, ZrxU1-xC, MoxU1-xC, and RhxU1-xC, including narrow frequency gaps and overlapping phonon modes, which increase the phonon scattering and lead to deterioration of thermal expansion coefficient (αV) and heat capacity (Cp) of UC predicted by the quasi harmonic approximation (QHA) method.

Electric field tunable multi-state tunnel magnetoresistances in 2D van der Waals magnetic heterojunctions

Magnetic tunnel junction (MTJ) based on van der Waals (vdW) magnetic layers has been found to present excellent tunneling magnetoresistance (TMR) property, which has great potential applications in field sensing, nonvolatile magnetic random access memories, and spin logics. Although MTJs composed of multilayer vdW magnetic homojunction have been extensively investigated, the ones composed of vdW magnetic heterojunction are still to be explored. Here, we use first-principles approaches to reveal that the magnetic heterojunction MTJs have much more distinguishable TMR values than the homojunction ones. In the MTJ composed of bilayer CrI3/bilayer Cr2Ge2Te6 heterojunction, we find there are eight stable magnetic states, leading to six distinguishable electronic resistances. As a result, five sizable TMRs larger than 300% can be obtained (the maximum TMR is up to 620 000%). Six distinguishable memories are obtained, which is two times larger than that of a four-layered homojunction MTJ. The underlying relationships among magnetic state, spin-polarized band structures, and transmission spectra are further revealed to explain the multiple TMR values. We also find that the magnetic states, and thus TMRs, can be efficiently modulated by an external electric field. This study opens an avenue to the design of high-performance MTJ devices based on vdW heterojunctions.

Effects of Mn content on austenite stability and mechanical properties of low Ni alumina-forming austenitic heat-resistant steel: a first-principles study

Low Ni alumina-forming austenitic (AFA) heat-resistant steel is an advanced high-temperature stainless steel with reduced cost, good machinability, high-temperature creep strength, and high-temperature corrosion resistance. Using the First-principles approach, this study examined the effect of Mn content on austenite stability and mechanical properties at the atomic level. Adding Mn to low Ni-AFA steel increases the unit cell volume with an accompanying increase in the absolute value of formation energy; the austenite formed more easily. The austenitic matrix binding energy decreases and remains negative, indicating austenite stability. As the Mn content increases from 3.2 to 12.8 wt%, the system's bulk modulus (B) rises significantly, and the shear modulus (G) falls. In addition, the system's strength and hardness decrease, and the Poisson ratio of the austenite matrix increases with improved elasticity; the system has excellent plasticity with an increase in the B/G. For the Fe22–Cr5–Ni3–Al2 system, with the increase of Mn content, the electron density distribution between the atoms is relatively uniform, and the electrons around the Mn atoms are slightly sparse, which will slightly reduce the structural stability of the matrix. The experiment demonstrated the matrix maintains the austenitic structure when adding 3.2–12.8 wt% Mn elements to low Ni-AFA steel. At an Mn content of 8 wt%, the overall mechanical properties of the high-Mn AFA steel are optimal, with a tensile strength of 581.64 MPa, a hardness of 186.17 HV, and an elongation of 39%.

Assessing factors that determine adatom migration and clustering on a thin film oxide; Pt1 and Rh1 on the “29” CuxO/Cu(1 1 1) surface

The dynamical nature of single-site catalysts under non-equilibrium conditions poses significant challenges in the full characterization of their active sites. The “29” oxide is a thin CuxO film grown on Cu(111) which provides a well-defined surface on which to study the structure and chemistry of atomically dispersed precious metals. A combination of experimental and first-principles approaches is used to investigate the factors that influence the mobility of metal adatoms and their clustering tendencies. Our work elucidates how a homogenous coordination environment of neutral single-atoms can be obtained when its tendency to break oxide bonds within its vicinity is low. We demonstrate that this in turn affects the chemical activity of atomically dispersed species on thin-film oxides, as defects on the oxide would in fact allow such species to be more accessible to CO. We thus highlight the importance of understanding the relationship between defects and atomically dispersed active sites upon designing single-site catalysts.

Transport properties in liquids from first-principles: The case of liquid water and liquid argon.

Shear and bulk viscosities of liquid water and argon are evaluated from first-principles in the density functional theory (DFT) framework, by performing molecular dynamics simulations in the NVE ensemble and using the Kubo-Greenwood equilibrium approach. The standard DFT functional is corrected in such a way to allow for a reasonable description of van der Waals effects. For liquid argon, the thermal conductivity has been also calculated. Concerning liquid water, to our knowledge, this is the first estimate of the bulk viscosity and of the shear-viscosity/bulk-viscosity ratio from first-principles. By analyzing our results, we can conclude that our first-principles simulations, performed at a nominal average temperature of 366 to guarantee that the systems are liquid-like, actually describe the basic dynamical properties of liquid water at about 330K. In comparison with liquid water, the normal, monatomic liquid Ar is characterized by a much smaller bulk-viscosity/shear-viscosity ratio (close to unity) and this feature is well reproduced by our first-principles approach, which predicts a value of the ratio in better agreement with experimental reference data than that obtained using the empirical Lennard-Jones potential. The computed thermal conductivity of liquid argon is also in good agreement with the experimental value.

Ab initio calculation of thermoelectric properties in 3d ferromagnets based on spin-dependent electron–phonon coupling

Crossed magneto-thermo-electric coefficients are central to novel sensors and spin(calori)tronic devices. Within the framework of Boltzmann’s transport theory, we calculate the resistivity and Seebeck coefficients of the most common 3d ferromagnetic metals: Fe, Co, and Ni. We use a fully first-principles variational approach, explicitly taking electron-phonon scattering into account. The electronic band structures, phonon dispersion curves, phonon linewidths, and transport spectral functions are reported, comparing with experimental data. Successive levels of approximation are discussed: constant relaxation time approximation, scattering for a non-magnetic configuration, then spin polarized calculations with and without spin–orbit coupling (enabling spin-flips). Spin polarization and explicit electron–phonon coupling are found to be necessary to reach a correct qualitative picture: the effect of spin flipping is substantial for resistivity and very delicate for the Seebeck coefficient. The spin-dependent Seebeck effect is also predicted.

A new carbon allotrope: Biphenylene as promising anode materials for Li-ion and Li[sbnd]O2 batteries

Using first-principles computational approaches, we investigate a new carbon allotrope, biphenylene, composed of tetragonal, hexagonal, and octagonal carbon rings as a promising material for Li-ion and LiO2 batteries. We find the Li/C ratio is <1/6 for the single-layer biphenylene which is similar to that of graphene. However, it can reach to lithium composition of Li1C6, Li1C4.5, Li1C4, Li1C3.75, and Li1C3 for bi-, tri-, tetra-, penta-layer, and bulk biphenylene, respectively. It is also found that Li is very mobile on both single-layer and bi-layer biphenylene based on the calculation results of the interaction between Li and substrate and Li diffusion. In addition, we also elucidate the electrochemical performance via the discharge−charge mechanism using Li/biphenylene as electrocatalyst materials of LiO2 battery. Gibbs free energy diagram of the discharge-charge mechanism is illustrated to examine the electrochemical performance. Our results reveal that biphenylene network can be a promising and low-cost catalyst for both Li-ion and LiO2 batteries.

Modulation of the magnetic, electronic, and optical behaviors of WS2 after metals adsorption: A first-principles study

The electronic, magnetic, and optical absorption properties of partial metal adsorbed WS2 systems were calculated by using the first-principles approach. The optimal adsorption sites corresponding to each metal adsorption on the WS2 system are diverse. The Pt-, Mg-, and Zn-WS2 systems are non-magnetic semiconductors, and the Ag-, Au-, Cr-, Fe-, Mn-, Mo-, Nb-, Ni-, and Ti-WS2 systems appear magnetic semiconductors. Whereas the Ca-, Li-, and Na-WS2 systems exhibit magnetic metal properties. The Ca- and Nb-WS2 systems have a significant red-shift tendency in the ultraviolet region. In particular, the adsorption of Ca and Nb enhance the absorption of WS2 in the ultraviolet region. The Nb-WS2 system has a strong absorption peak intensity that reached 1.09◊105 cm−1 at 448.3 nm. Therefore, metal adsorbed WS2 systems will be helpful for the studying of nano-spintronics and photovoltaics devices.

Phonon-assisted optical absorption of SiC polytypes from first principles

Silicon carbide (SiC) is an indirect-gap semiconductor material widely used in electronic and optoelectronic applications. While experimental measurements of the phonon-assisted absorption coefficient of SiC across its indirect gap have existed for more than 50 years, theoretical investigations of phonon-assisted absorption have been hampered by their excessive computational cost. In this work, we calculate the phonon-assisted temperature-dependent optical absorption spectra of the commonly occurring SiC polytypes (3C, 2H, 4H, 6H, and 15R), using first-principles approaches based on density functional theory and related techniques. We show that our results agree with experimentally determined absorption coefficients in the spectral region between the direct and indirect band gaps. The temperature dependence of the spectra can be well predicted with taking the temperature dependence of the band gaps into account. Lastly, we compare the spectra obtained with second-order perturbation theory to those determined by the special displacement method and we show that the full consideration of the electronic energy renormalization due to temperature is important to further improve the prediction of the phonon-assisted absorption in SiC. Our insights can be applied to predict the optical spectra of the less common SiC polytypes and other indirect-gap semiconductors in general.

Fluorine substitution and pre-sodiation strategies to boost energy density of V-based NASICON-structured SIBs: Combined theoretical and experimental study

The conventional V-based NASICON-type symmetric sodium-ion batteries (SSIBs) suffer from insufficient energy density mainly due to the low operating voltage. In this study, a novel high-voltage quasi-SSIB (Q-SSIB) was designed by coupling a high-voltage F-substituted cathode (Na3V2(PO4)2F3@rGO) with a low-voltage pre-sodiated anode (Na4V2(PO4)3@rGO) by combining experimental and the first-principles approaches. The electrochemical performance of the cathode was improved by slightly regulating the pH value of the precursor solution to optimize the balance between its crystallization quality and purity, with introducing surface energy analysis to help elucidate the mechanism. An electrochemical pre-intercalation strategy was adopted to synthesize the sodium-rich anode. Besides, the ionic diffusion properties of electrodes were systematically studied by combining DSCV, GITT tests and density functional theory (DFT) calculations, demonstrating that the anode presents faster kinetics in the pre-sodiated phase and shows favorable kinetics compatibility with the cathode. The Na4V2(PO4)3//Na3V2(PO4)2F3 Q-SSIB exhibits a high energy density of 340.1 Wh kg−1 and a maximum output voltage plateau of 3.75 V, highly improved compared to the ones (1.8 V, 211 Wh kg−1) in Na3V2(PO4)3 SSIBs. This work provides references from theoretical design to experimental study for boosting the energy density of NASICON-type SIBs for broadening their application prospects in energy storage.

Quantitative Solvation Energies from Gas-Phase Calculations: First-Principles Charge Transfer and Perturbation Approaches.

We present a first-principles approach for the calculation of solvation energies and enthalpies with respect to different ion pair combinations in various solvents. The method relies on the conceptual density functional theory (DFT) of solvation, from which detailed expressions for the solvation energies can be derived. In addition to fast and straightforward gas phase calculations, we also study the influence of modified chemical reactivity descriptors in terms of electronic perturbations. The corresponding phenomenological changes in molecular energy levels can be interpreted as the influence of continuum solvents. Our approach shows that the introduction of these modified expressions is essential for a quantitative agreement between the calculated and the experimental results.