Local screened Coulomb correction approach to strongly correlated d-electron systems

Ultrafast Hole Trapping in Te-MoTe2-MoSe2/ZnO S-Scheme Heterojunctions for Photochemical and Photo-/Electrochemical Hydrogen Production

Te-MoTe2-MoSe2/ZnO S-scheme heterojunctions are engineered to ascertain the advanced redox ability in sustainable HER operations. Photo-physical studies have established the steady state transfer of photo-induced charge carriers whereas an improved transfer dynamics realized by state-of-art ultrafast transient absorption and irradiated-XPS analysis of optimized 5wt% Te-MoTe2-MoSe2/ZnO heterostructure. 2.5, 5, and 7.5wt% Te-MoTe2-MoSe2/ZnO photocatalysts (2.5MTMZ, 5MTMZ and 7.5MTMZ) exhibited 2.8, 3.3, and 3.1-fold higher HER performance than pristine ZnO with marvelous apparent quantum efficiency of 35.09%, 41.42% and 38.79% at HER rate of 4.45, 5.25, and 4.92 mmol/gcat/h, respectively. Electrochemical water splitting experiments manifest subdued 583 and 566 mV overpotential values of 2.5MTMZ and 5MTMZ heterostructures to achieve 10 mA cm-2 current density for HER, and 961 and 793 mV for OER, respectively. For optimized 5MTMZ photocatalyst, lifetime kinetic decay of interfacial charge transfer step is evaluated to be 138.67 ps as compared to 52.92 ps for bare ZnO.

Doubly Screened Coulomb Correction Approach for Strongly Correlated Systems

Strongly correlated systems containing d/f electrons present a challenge to conventional density functional theory such as the local density approximation or generalized gradient approximation. We developed a doubly screened Coulomb correction (DSCC) approach to perform on-site Coulomb interaction correction for strongly correlated materials. The on-site Coulomb interaction between localized d/f electrons is self-consistently determined from a model dielectric function that includes both the static dielectric and Thomas-Fermi screening. We applied DSCC to simulate the electronic and magnetic properties of typical 3d, 4f, and 5f strongly correlated systems. The accuracy of DSCC is comparable to that of hybrid functionals but an order of magnitude faster. In addition, DSCC can reflect the difference in the Coulomb interaction between metallic and insulating situations, similar to the popular but computationally expensive constrained random phase approximation approach. This feature suggests that DSCC is also a promising method for simulating Coulomb interaction parameters.

Comparative study of first-principles approaches for effective Coulomb interaction strength Ueff between localized f-electrons: Lanthanide metals as an example

As correlation strength has a key influence on the simulation of strongly correlated materials, many approaches have been proposed to obtain the parameter using first-principles calculations. However, a comparison of the different Coulomb strengths obtained using these approaches and an investigation of the mechanisms behind them are still needed. Taking lanthanide metals as an example, we research the factors that affect the effective Coulomb interaction strength, U_eff, by local screened Coulomb correction (LSCC), linear response (LR), and constrained random-phase approximation (cRPA) in the Vienna Ab initio Simulation Package. The U_eff ^LSCC value increases from 4.75 to 7.78 eV, U_eff ^LR is almost stable at about 6.0 eV (except for Eu, Er, and Yb), and U_eff ^cRPA shows a two-stage decreasing trend in both light and heavy lanthanides. To investigate these differences, we establish a scheme to analyze the coexistence and competition between the orbital localization and the screening effect. We find that LSCC and cRPA are dominated by the orbital localization and the screening effect, respectively, whereas LR shows the balance of the competition between the two factors. Additionally, the performance of these approaches is influenced by different starting points from the Perdew-Burke-Ernzerhof (PBE) and PBE + U, especially for cRPA. Our results provide useful knowledge for understanding the U_eff of lanthanide materials, and similar analyses can also be used in the research of other correlation strength simulation approaches.

Quasi-solid-state Zn-air batteries with an atomically dispersed cobalt electrocatalyst and organohydrogel electrolyte

Quasi-solid-state Zn-air batteries are usually limited to relatively low-rate ability (<10 mA cm-2), which is caused in part by sluggish oxygen electrocatalysis and unstable electrochemical interfaces. Here we present a high-rate and robust quasi-solid-state Zn-air battery enabled by atomically dispersed cobalt sites anchored on wrinkled nitrogen doped graphene as the air cathode and a polyacrylamide organohydrogel electrolyte with its hydrogen-bond network modified by the addition of dimethyl sulfoxide. This design enables a cycling current density of 100 mA cm-2 over 50 h at 25 °C. A low-temperature cycling stability of over 300 h (at 0.5 mA cm-2) with over 90% capacity retention at -60 °C and a broad temperature adaptability (-60 to 60 °C) are also demonstrated.

DFT+U within the framework of linear combination of numerical atomic orbitals

We present a formulation and implementation of the density functional theory (DFT)+U method within the framework of linear combination of numerical atomic orbitals (NAO). Our implementation not only enables single-point total energy and electronic-structure calculations but also provides access to atomic forces and cell stresses, hence allowing for full structure relaxations of periodic systems. Furthermore, our implementation allows one to deal with non-collinear spin texture, with the spin-orbit coupling (SOC) effect treated self-consistently. The key aspect behind our implementation is a suitable definition of the correlated subspace when multiple atomic orbitals with the same angular momentum are used, and this is addressed via the "Mulliken charge projector" constructed in terms of the first (most localized) atomic orbital within the d/f angular momentum channel. The important Hubbard U and Hund J parameters can be estimated from a screened Coulomb potential of the Yukawa type, with the screening parameter either chosen semi-empirically or determined from the Thomas-Fermi screening model. Benchmark calculations are performed for four late transition metal monoxide bulk systems, i.e., MnO, FeO, CoO, and NiO, and for the 5d-electron compounds IrO₂. For the former type of systems, we check the performance of our DFT+U implementation for calculating bandgaps, magnetic moments, electronic band structures, as well as forces and stresses; for the latter, the efficacy of our DFT+U+SOC implementation is assessed. Systematic comparisons with available experimental results, especially with the results from other implementation schemes, are carried out, which demonstrate the validity of our NAO-based DFT+U formalism and implementation.

First principles investigation of electron correlation and Lifshitz transition within iron polynitrides

Metal poly-nitrogen compounds are gaining great interests as potential high energy density materials. Several iron polynitrides have been recently synthesized and investigated under high pressure (2018Nature Communications92756). In this work the electron correlations within these iron poly-nitrogen compounds were self-consistently determined, benchmarked with those obtained from linear response approach. Along with the increase of the concentration of nitrogen, the Coulomb interaction strengths show a monotonic decrease, where FeN and FeN₂are antiferromagnetic and the others are ferromagnetic. Then the electron correlation is studied along with the pressure, where the electrons are more delocalized as pressure becomes higher. One electronic topological transition was found for FeN₂, owing to a breaking of symmetry of spin and a transition of magnetism induced by a structural change. The band structure, densities of states, Fermi surface and absorption spectra were calculated and discussed.

Electron correlation effect versus spin-orbit coupling for tungsten and impurities

The electron correlation and spin-orbit coupling (SOC) effects are investigated for body-centered-cubic tungsten and intrinsic & irradiative impurities using first principles calculations based upon the density functional theory. It is found that the electron correlation between the localized 5delectrons and the SOC effect are significant in modifying the band structures and the formation energies of defects. For the latter one, the involving of electron correlation always makes the defects stabler than the Perdew-Burke-Ernzerhof results, while the SOC contributes diversely for different defects. Moreover, the migration barrier of single tungsten vacancy moving in ⟨111⟩ direction is explored, where the inclusion of electron correlations remarkably decreases the migration barrier, while the influence of SOC is almost negligible. This study can help to validate the previous studies on irradiative defects in tungsten and improve the further investigations.

Electronic, magnetic and optical properties of transition-metal and hydroxides doped monolayer g-C3N4: a first principles investigation

The graphitic carbon nitride (g-C3N4) is a promising layered two-dimension material with an opened bandgap. It is of interest to explore the tunability of the bandgap together with the magnetism by doping transition metal atoms. In this work, we investigated the transition metals (Mn, Fe, Co, Ni) and their hydroxides doped g-C3N4monolayers. The electron correlations between the 3delectrons of the doped transition metal atoms are self-consistently calculated and analyzed based on the density functional theory. The magnetism, electronic band structures and optical properties are systematically investigated. It reveals that the transition metal doped g-C3N4is ferromagnetic (FM) state at small doping concentration, where the two spins show different bandgaps. When the doping is high enough, it turns to metallic antiferromagnetic (AFM) state except that Mn doped g-C3N4is metallic FM state. On another hand, the system shows variable absorption spectra at different doping level. When the vacancy sites are fully occupied, a large absorption peak appears around 1.5 eV suitable for visible light. Moreover, within the transition metal hydroxides doped g-C3N4, the global ground state shows as AFM, and the absorption spectra within low energy range is distinct due to the presence of hydroxyl group. Therefore, doping with transition metal atoms and hydroxides can effectively tune the bandgap, magnetism and optical properties of g-C3N4so as to promote its applications.