Plane-wave Density Functional Theory Research Articles

Dual-Grid and Mixed-Precision Methods for Accelerating Plane-Wave Hybrid Functional Electronic Structure Calculations.

Hybrid functionals that incorporate exact Hartree-Fock exchange (HFX) into density functional theory (DFT) are crucial for accurately predicting the electronic structures of extended systems in condensed-matter physics and materials science. Although the exact exchange contributes only a small fraction of the total energy, HFX calculations in hybrid functionals demand significant computational resources. Here, we introduce dual-grid and mixed-precision techniques, based on two low-rank approximations, adaptively compressed exchange (ACE) and interpolative separable density fitting (ISDF) methods, to significantly improve the computational efficiency of plane-wave hybrid functional calculations in the software package PWDFT (plane wave density functional theory). The dual-grid method introduces a smaller cutoff energy, thereby reducing the number of Fourier and real-space grids involved in the HFX calculations. The mixed-precision method reduces the computational cost by shifting from double precision to single precision during the HFX construction while maintaining double precision for other DFT processes. Numerical results demonstrate that both the dual-grid and mixed-precision techniques can accelerate plane-wave hybrid functional calculations several times, with an acceptable trade-off in accuracy compared to the original low-rank approximations. Furthermore, by utilizing a hybrid MPI and OpenMP parallel implementation, we successfully perform large-scale plane-wave hybrid functional calculations with up to 8,000 silicon atoms using 16,000 CPU cores.

The EFG Rosetta Stone: translating between DFT calculations and solid state NMR experiments.

We present a comprehensive study on the best practices for integrating first principles simulations in experimental quadrupolar solid-state nuclear magnetic resonance (SS-NMR), exploiting the synergies between theory and experiment for achieving the optimal interpretation of both. Most high performance materials (HPMs), such as battery electrodes, exhibit complex SS-NMR spectra due to dynamic effects or amorphous phases. NMR crystallography for such challenging materials requires reliable, accurate, efficient computational methods for calculating NMR observables from first principles for the transfer between theoretical material structure models and the interpretation of their experimental SS-NMR spectra. NMR-active nuclei within HPMs are routinely probed by their chemical shielding anisotropy (CSA). However, several nuclear isotopes of interest, e.g.7Li and 27Al, have a nuclear quadrupole and experience additional interactions with the surrounding electric field gradient (EFG). The quadrupolar interaction is a valuable source of information about atomistic structure, and in particular, local symmetry, complementing the CSA. As such, there is a range of different methods and codes to choose from for calculating EFGs, from all-electron to plane wave methods. We benchmark the accuracy of different simulation strategies for computing the EFG tensor of quadrupolar nuclei with plane wave density functional theory (DFT) and study the impact of the material structure as well as the details of the simulation strategy. Especially for small nuclei with few electrons, such as 7Li, we show that the choice of physical approximations and simulation parameters has a large effect on the transferability of the simulation results. To the best of our knowledge, we present the first comprehensive reference scale and literature survey for 7Li quadrupolar couplings. The results allow us to establish practical guidelines for developing the best simulation strategy for correlating DFT to experimental data extracting the maximum benefit and information from both, thereby advancing further research into HPMs.

DFT investigation of the impact of inner-sphere water molecules on RE nitrate binding to internal pore and external surface of MCM-22.

The impact of inner-sphere water molecules on the binding of rare earth (RE) nitrates to MCM-22 aluminosilicates is analyzed. We used cluster models of MCM-22 to investigate the binding phenomena through localized-basis density functional theory (DFT) calculations. We also conducted plane-wave DFT calculations for a few selected binding configurations using the entire periodic MCM-22 unit cell to check for consistency. Two different MCM-22 cluster models are developed to represent an internal pore and an external surface. Starting with pure silica MCM-22, we substituted one Si with Al and added a H atom on the O bridging the Si and Al to create a Brønsted acid site (BAS), Si-{OH}-Al. Specifically, we investigated the binding of two RE nitrate aqua complexes, [X(NO3)3(H2O)n] where n = 4 (3) for X = Nd (Yb) via the reaction X(NO3)3(H2O)n + Si-{OH}-Al → Si-{OX(NO3)2(H2O)n}-Al + HNO3 at BASs, and via an analogous reaction at silanol sites, Si-{OH}. The above analysis just includes the inner coordination sphere H2O. Actually, for the Nd (Yb) complex, after binding at the T1 and T2 sites (T1 site) within the internal pore, one of the H2O molecules leaves this inner sphere. The binding strength at BASs and silanol sites is calculated from the energy change during the above reactions. One finds that Nd complexes prefer binding at the internal pore, while Yb complexes have a comparable binding preference both at the internal pore and external surface. The cluster calculations show good agreement with periodic calculations, implying that the cluster models are suitable for binding studies. Compared to the binding of non-hydrated RE nitrates, the explicit H2O molecules have a minimal impact on overall binding energy trends, but they do increase individual binding energy values. This study also demonstrated the stronger binding affinity of BASs over silanol sites.

Investigating Activity and Stability of Mixed-Metal Oxides (M-NiO) for Anion Exchange Membrane Electrolysis

Recent experimental studies suggest mixed oxides of Ni, Co, and Fe operated in basic media may be the strongest alternative to iridium.1, 2 However, the efficiency of these catalysts is strongly synthesis-dependent and there is no established understanding of the role of the different metals in operation with ionomers. Notably, Trotochaud, et al. observed catalyst efficiency in the order Ni0.9Fe0.1Ox > NiOx > NiyCo1-y, whereas Morales-Guio, et. al. ranked FeNiOx, CoFeNiOx > CoNiOx > NiOx.1, 2 Anderson et al. found in their RDE studies of commercial catalysts that NiFe2O4outperformed NiO, Co3O4 by 7 times kinetically. In low concentrations, these mixed-oxide materials may behave more closely to doped-catalysts, where dopants can increase activity, change selectivity, and even improve resistance to poisoning of active sites.3-6 Understanding how and why these catalysts work, and do not work, is critical to enabling these materials to achieve the Hydrogen Shot goal of $1/kg H2 in 1 decade. For our theoretical model, we limited our mixed material model to a single dopant to fully examine the geometric and electronic effects of a nearby transition metal e.g., Fe and Co dopants. Plane-wave density functional theory calculations elucidated the dopant-effects on both activity (the oxygen evolution reaction) and stability in anion exchange membrane electrolysis in the presence of experimentally-relevant ionomers (Georgia Tech, Nafion, Versogen, and Sustainion).(1) Trotochaud, L.; Ranney, J. K.; Williams, K. N.; Boettcher, S. W. Solution-cast metal oxide thin film electrocatalysts for oxygen evolution. Journal of the American Chemical Society 2012, 134 (41), 17253-17261.(2) Morales-Guio, C. G.; Liardet, L.; Hu, X. Oxidatively electrodeposited thin-film transition metal (oxy) hydroxides as oxygen evolution catalysts. Journal of the American Chemical Society 2016, 138 (28), 8946-8957.(3) Ha, M.-A.; Dadras, J.; Alexandrova, A. Rutile-deposited Pt–Pd clusters: A hypothesis regarding the stability at 50/50 ratio. ACS Cat. 2014, 4(10), 3570-3580.(4) Baxter, E. T.; Ha, M.-A.; Cass, A. C.; Alexandrova, A. N.; Anderson, S. L. Ethylene Dehydrogenation on Pt4, 7, 8 Clusters on Al2O3: Strong Cluster Size Dependence Linked to Preferred Catalyst Morphologies. ACS Cat. 2017, 7 (5), 3322-3335.(5) Ha, M.-A.; Baxter, E. T.; Cass, A. C.; Anderson, S. L.; Alexandrova, A. N. Boron switch for selectivity of catalytic dehydrogenation on size-selected Pt clusters on Al2O3. Journal of the American Chemical Society 2017, 139 (33), 11568-11575.(6) Halder, A.; Ha, M.-A.; Zhai, H.; Yang, B.; Pellin, M. J.; Seifert, S.; Alexandrova, A. N.; Vajda, S. Oxidative Dehydrogenation of Cyclohexane by Cu vs Pd Clusters: Selectivity Control by Specific Cluster Dynamics. ChemCatChem 2020, 12 (5), 1307-1315. DOI: 10.1002/cctc.201901795. Figure 1

Investigating Ionomer Interactions on the Catalytic Interface of Model Catalysts (NiO, IrO2)

Anion exchange membrane electrolysis enables the use of earth abundant metals for the catalyst and other components of the membrane electrode assembly. However, earth abundant metal catalysts may be sensitive to poisoning and degradation due to the extreme pH of the electrolyte or interactions with the ionomer. Plane-wave density functional theory calculations probed the binding strength of different functional groups from popular ionomers (Nafion, Sustainion, tetramethylammonium-based ETFE/Gen 2/Georgia Tech, Versogen) on model catalysts such as Platinum Group Metal IrO2 and earth abundant NiO.1 We evaluated the stability of these various ionomers on these model catalysts, whether they remain intact or degrade, as well as their catalytic effects on the oxygen evolution reaction (OER) e.g. in the presence of OH*. These calculations allowed us to understand the poisoning of active sites: 1) if the functional group bound more strongly than key reaction intermediates, then the ionomer effectively blocked activity by displacing the reaction intermediate; 2) if the functional group introduced competing reactions, then the ionomer was consuming the OxHy* intermediates necessary for OER. Ideally, ionomers remain stable in contact with the catalyst and shuttle hydroxide ions from the cathode to the anode.1. S. Ghoshal, B. S. Pivovar and S. M. Alia, J. Power Sources, 2021, 488, 229433. Figure 1

Experimental Evaluation and Density Functional Theory Analysis of Activation Barriers in Dry Reforming Reaction Using Ni Nanoparticle-Supported CeO2 Novel Flower-like Catalyst

IntroductionIn the realm of renewable energy, biomass emerges as a crucial resource, capable of generating methane through anaerobic fermentation. This methane, in its role as a hydrogen carrier, presents an opportunity for fuel cells to leverage their high efficiency in electricity generation. Recent studies have illuminated the potential of biomass utilization, particularly in converting waste from shrimp farming into methane[1][2]. The prospect of utilizing revenue from shrimp farming to offset investments in fuel cells underscores the symbiotic relationship between these industries and drives interest in exploring new avenues for sustainable energy production.Efficient extraction of hydrogen from methane is an important factor in optimizing the fuel cell systems described above. Consequently, there has been a burgeoning focus on improving the efficiency of the dry reforming of methane (DRM) reaction. Within this context, CeO2 loaded with Ni nanoparticles has emerged as a promising catalyst, holding the potential to innovate methane utilization in fuel cells. This study embarks on a meticulous investigation into the dissociation reactions of methane and carbon dioxide, key steps in the DRM reaction, aiming to elucidate the underlying mechanisms and enhance reaction efficiency.MethodologyThe methodology employed in this study density functional theory (DFT) to calculate activation barriers for each dissociation reaction. Leveraging the plane-wave DFT method within the Vienna ab initio simulation package (VASP), the study explores diverse configurations of tetrahedral Ni nanoparticles on CeO2(111) surfaces. Through the nudged elastic band (NEB) method, activation barriers for methane and carbon dioxide dissociation were determined for each configuration. To validate these computational findings, experimental DRM reaction tests were conducted utilizing a Ni nanoparticle-supported flower-shaped CeO2 catalyst specifically synthesized for this study. Then, the activation barriers were calculated from the amount of hydrogen gas produced and methane consumed, offering a comprehensive understanding of reaction kinetics.Results and discussionResults from the study reveal intriguing insights into methane dissociation kinetics. The activation barrier for methane dissociation is found to range from 0.80 eV to 1.03 eV, depending on the loading site of Ni nanoparticles, closely mirroring the value derived from experimental methane consumption rates (=0.67 eV). On the other hand, the dissociation of carbon dioxide exhibits higher activation barriers compared to methane dissociation, suggesting its role as a rate-limiting step in the DRM reaction. Particularly noteworthy is the study's suggestion that augmenting the positive charge of Ni nanoparticles may enhance methane dissociation, offering a promising avenue for catalyst optimization in DRM processes.[1] Y. Shiratori et al., Biogas Power Generation with SOFC to Demonstrate Energy Circulation Suitable for Mekong Delta, Vietnam. Fuel Cells 19, 346-353 (2019).[2] P. H. Tu et al., Paper‐structured catalyst with a dispersion of ceria‐based oxide support for improving the performance of an SOFC fed with simulated biogas. Fuel Cells, 1-11 (2024).

An alternative GPU acceleration for a pseudopotential plane-waves density functional theory code with applications to metallic systems

We present an alternative GPU acceleration for plane waves pseudopotentials electronic structure codes designed for systems that have small unit cells but require a large number of k points to sample the Brillouin zone as happens, for instance, in metals. We discuss the diagonalization of the Kohn and Sham equations and the solution of the linear system derived in density functional perturbation theory. Both problems take advantage from a rewriting of the routine that applies the Hamiltonian to the Bloch wave-functions to work simultaneously (in parallel on the GPU threads) on the wave-functions with different wave-vectors k, as many as allowed by the GPU memory. Our implementation is written in CUDA Fortran and makes extensive use of kernel routines that run on the GPU (GLOBAL routines) or can be called from inside the GPU kernel (DEVICE routines). We compare our method with the CPUs only calculation and with the approach currently implemented in Quantum ESPRESSO that uses GPU accelerated libraries for the FFT and for the linear algebra tasks such as the matrix-matrix multiplications as well as OpenACC directives for loop parallelization. We show in a realistic example that our method can give a significant improvement in the cases for which it has been designed.

Automated optimization and uncertainty quantification of convergence parameters in plane wave density functional theory calculations

First principles approaches have revolutionized our ability in using computers to predict, explore, and design materials. A major advantage commonly associated with these approaches is that they are fully parameter-free. However, numerically solving the underlying equations requires to choose a set of convergence parameters. With the advent of high-throughput calculations, it becomes exceedingly important to achieve a truly parameter-free approach. Utilizing uncertainty quantification (UQ) and linear decomposition we derive a numerically highly efficient representation of the statistical and systematic error in the multidimensional space of the convergence parameters for plane wave density functional theory (DFT) calculations. Based on this formalism we implement a fully automated approach that requires as input the target precision rather than convergence parameters. The performance and robustness of the approach are shown by applying it to a large set of elements crystallizing in a cubic fcc lattice.

Theoretical and experimental investigation of BaY2(MoO4)4:xSm3+ phosphors

In this paper, the novel BaY2(MoO4)4:xSm3+ phosphors with strong red emission and high thermal stabilization were prepared by a conventional method of high temperature solid state reaction in air atmosphere. Morphology, phase purity, element distribution, UV–Vis–NIR diffuse reflectance spectroscopy (DRS), and luminescence properties were investigated in detail. The crystal structure of the BaY2(MoO4)4 host was refined with the aid of the Rietveld refinement method by the GSAS program. The electronic band structure and phonon dispersion were performed using plane-wave density functional theory (DFT). The prepared BaY2(MoO4)4:Sm3+ phosphor exhibits excellent red emission under near-ultraviolet excitation. Strong red emission intensity and high thermal stability suggest potential application in backlighting or phosphor-covered white light-emitting diodes (pc-LEDs).

Implementation of frozen density embedding in CP2K and OpenMolcas: CASSCF wavefunctions embedded in a Gaussian and plane wave DFT environment.

Most chemical processes happen at a local scale where only a subset of molecular orbitals is directly involved and only a subset of covalent bonds may be rearranged. To model such reactions, Density Functional Theory (DFT) is often inadequate, and the use of computationally more expensive correlated wavefunction (WF) methods is required for accurate results. Mixed-resolution approaches backed by quantum embedding theory have been used extensively to approach this imbalance. Based on the frozen density embedding freeze-and-thaw algorithm, we describe an approach to embed complete active space self-consistent field simulations run in the OpenMolcas code in a DFT environment calculated in CP2K without requiring any external tools. This makes it possible to study a local, active part of a chemical system in a larger and relatively static environment with a computational cost balanced between the accuracy of a WF method and the efficiency of DFT, which we test on environment-subsystem pairs. Finally, we apply the implementation to an oxygen molecule leaving an aluminum (111) surface and a ruthenium(IV) oxide (110) surface.

Generalizing deep learning electronic structure calculation to the plane-wave basis.

Deep neural networks capable of representing the density functional theory (DFT) Hamiltonian as a function of material structure hold great promise for revolutionizing future electronic structure calculations. However, a notable limitation of previous neural networks is their compatibility solely with the atomic-orbital (AO) basis, excluding the widely used plane-wave (PW) basis. Here we overcome this critical limitation by proposing an accurate and efficient real-space reconstruction method for directly computing AO Hamiltonian matrices from PW DFT results. The reconstruction method is orders of magnitude faster than traditional projection-based methods to convert PW results to the AO basis, and the reconstructed Hamiltonian matrices can faithfully reproduce the PW electronic structure, thus bridging the longstanding gap between the AO basis deep learning electronic structure approach and PW DFT. Advantages of the PW methods, such as high accuracy, high flexibility and wide applicability, thus can be all integrated into deep learning electronic structure methods without sacrificing these methods' inherent benefits. This allows for the construction of large-scale and high-fidelity training datasets with the help of PW DFT results towards the development of precise and broadly applicable deep learning electronic structure models.

First-principles study on the mechanism of Hf and Ti doping promoting hydrogen release in ZrCoH3

This paper reveals the mechanism of Hf and Ti doping promoting hydrogen release in ZrCoH3. Different from previous experimental methods, this study employs the plane wave pseudopotential method and density functional theory to predict the relationship between the formation energy and electronic structure of the ZrCoH3-Hf/Ti system, and uses theoretical calculations to guide the modification design of ZrCoH3. Firstly, by calculating the thermodynamic properties of the ZrCoH3-Hf/Ti system and combining the density of states theory, the bonding characteristics and dehydrogenation preference between H atoms and neighboring metal atoms in the ZrCoH3-Hf/Ti system are determined. Additionally, the electronic structure of the ZrCoH3-Hf/Ti system is calculated to elucidate the hybridization of bonding and antibonding orbitals between atoms in the ZrCoH3-Hf/Ti system. Moreover, DCo-d is utilized to measure the strength of antibonding interactions in the ZrCoH3-Hf/Ti system. The main cause of antibonding interactions in the ZrCoH3-Hf/Ti system is attributed to the variation in formation energy, and the change in antibonding interactions is sensitive to the variation in formation energy. Finally, a feasible method to improve the properties of ZrCoH3 is proposed, which involves modifying the electronic structure to increase the partial density of states at the Fermi energy level, making the formation energy of hydrides less negative and forcing the structure to be more unstable. This method has potential application value in the modification of ZrCoH3.

First-principles calculations to investigate phase stability, elastic and thermodynamic properties of TiMoNbX (X=Cr, Ta, Cr and Ta) refractory high entropy alloys

This work uses first-principles calculations to investigate the phase stability, thermophysical and mechanical properties of refractory high entropy alloys (RHEAs) at finite temperatures. On the basis of plane wave quasi-potential and density functional theory, construct the structure model of a solid solution. The TiMoNbX (X = Cr, Ta, Cr and Ta) RHEAs have been determined to preserve a single body-centered cubic solid solution structure by calculations and the equilibrium lattice parameters and elastic modulus are consistent with experimental data obtained by laser cladding, which is combined with TC4 (Ti-6Al-4V) substrate. Using the quasi-harmonic Debye-Grüneisen model, the thermophysical characteristics of three RHEAs are investigated. The Voigt-Reuss-Hill scheme is used for calculating the Young's modulus (E), bulk modulus (B), shear modulus (G), and Poisson's ratio (ν), which indicates that all three RHEAs are ductile materials. Additionally, the modulus and hardness of materials decrease as temperature rises, whereas the properties of TiMoNbX RHEAs are predicted, as the nanoindentation hardness values at room temperature are comparable to, and slightly higher than the calculated values.

Improving the precision of work-function calculations within plane-wave density functional theory

Abstract Work function is a fundamental property of metals and is related to many surface-related phenomena of metals. Theoretically, it can be calculated with a metal slab supercell in density functional theory (DFT) calculations. In this paper, we discuss how the commensurability of atomic structure with the underlying fast Fourier transform (FFT) grid affects the accuracy of work function obtained from plane-wave pseudopotential DFT calculations. We show that the macroscopic average potential, which is an important property in work function calculations under the ‘bulk reference’ method, is more numerically stable when it is calculated with commensurate FFT grids than with incommensurate FFT grids. Due to the stability of the macroscopic average potential, work function calculated with commensurate FFT grids shows better convergence with respect to basis set size, vacuum length and slab thickness of a slab supercell. After we control the FFT grid commensurability issue in our work function calculations, we obtain well-converged work functions for Al, Pd, Au and Pt of (100), (110) and (111) surface orientations. For all the metals considered, the ordering of our calculated work functions of the three surface orientations agrees with experiment. Our findings reveal the importance of the FFT grid commensurability issue, which is usually neglected in practice, in obtaining accurate metal work functions, and are also meaningful to other DFT calculations which can be affected by the FFT grid commensurability issue.

First principles validation of energy barriers in Ni75Al25

Precipitates in nickel-based superalloys form during heat treatment on a time scale inaccessible to direct molecular dynamics simulation, but can be studied using kinetic Monte Carlo (KMC) modelling. This requires reliable values for the barrier energies separating distinct configurations over the trajectory of the system. In this study, we validate vacancy migration barriers found with the Activation-Relaxation Technique nouveau (ARTn) method in partially ordered Ni75Al25 with a monovacancy using published potentials for the atomic interactions against first-principles methods. In a first step, we confirm that the ARTn barrier energies agree with those determined with the nudged elastic band (NEB) method. As the number of atoms used in those calculations is too great for direct ab initio calculations, we cut the cell size to 255 atoms, thus controlling finite size effects. We then use the plane-wave density functional theory code CASTEP and its inbuilt NEB method in the smaller cells. This provides us with a continuous validation chain from first principles to KMC simulations with interatomic potentials (IPs). We evaluate the barrier energies of five further IPs with NEB, demonstrating that none yields values with sufficient reliability for KMC simulations, with some of them failing completely. This is a first step towards quantifying the errors incurred in KMC simulations of precipitate formation and evolution.

Enhanced figure of merit in two-dimensional ZrNiSn nanosheets for thermoelectric applications

A novel two-dimensional (2D) half-Heusler ZrNiSn nanosheet for thermoelectric applications was designed from bulk half-Heusler ZrNiSn through first-principles calculation. Investigation of bulk half-Heusler and 2D nanosheet ZrNiSn was performed with the Quantum Espresso code based on a density functional theory plane wave basis set. Electronic band structure and density of states calculations were used to study the confinement effects. On moving from bulk to 2D a change of structure is observed from face-centered cubic to trigonal due to confinement effects. The semiconducting nature of bulk ZrNiSn is undisturbed while moving to a 2D nanosheet; however, the band gap is widened from 0.46 to 1.3 eV due to the restricted motion of electrons in one direction. Compared with bulk ZrNiSn, 2D nanosheets were found to have a higher Seebeck coefficient a lower thermal conductivity and higher figure of merit, which makes 2D ZrNiSn nanosheets suitable for thermoelectric applications. Atomically thin 2D structures with a flat surface have the potential to form van der Waals heterojunctions, paving the way for device fabrication at the nanoscale level.

Strain-dependent one-dimensional confinement channels in twisted bilayer 1T′−WTe2

The low-symmetry and anistropic lattice of 1T′WTe2 is responsible for the existence of parallel one-dimensional channels in the moiré patterns of twisted bilayers. This gives the opportunity to explore moiré physics of a different nature to that widely observed in twisted bilayers of materials with hexagonal symmetries. Here, we combine plane-wave and linear-scaling density functional theory calculations to describe the electronic properties of twisted bilayer 1T′WTe2. We investigate the strain dependence of both aligned bilayer configurations across a range of stacking geometries, and of the twisted bilayer itself. For a small change in the lattice parameters of the constituent 1T′WTe2 monolayers, we find a very substantial increase in the moiré-induced striped electrostatic potential landscape in the twisted bilayer. We measure a peak-to-trough magnitude >200 meV between parallel linear channels, sufficient to induce Luttinger liquid behavior. Published by the American Physical Society 2024

First principles calculation and corrosion resistance study of Fe60CrxNi40-x medium entropy alloy

In this paper, Fe60CrxNi40-x medium entropy alloys (MEAs) were synthesized through vacuum arc melting. Based on the plane wave pseudo-potential and density functional theory, the solid solution structure is modeled by virtual crystal approximation (VCA). The first principle method was employed to examine how Cr content affects the phase structure, elastic constant, and elastic properties of the Fe60CrxNi40-x. Physical phase analysis of the MEAs by X-ray diffraction reveals that the Fe60CrxNi40-x maintain a single FCC solid solution structure. Meanwhile, the impact of Cr content on MEAs' resistance to corrosion in a Cl- setting was examined and contrasted with 316 L stainless steel. The result indicated that as the Cr content rises, the MEAs exhibit an extended passivation period, a reduced dimensional passivation current, and a more compact and stable passivation film. When considering the aggregate outcomes of pitting potential (Epit), self-corrosion potential (Ecorr), and corrosion current density (icorr) for 316LSS and MEAs, it's evident that Fe60CrxNi40-x in 3.5 wt% NaCl solution exhibits superior corrosion resistance compared to 316 L stainless steel, with Fe3 alloy leading in corrosion resistance among medium entropy alloys.

Enhanced hydrogen adsorption-desorption reversibility found on NiAl alloy: A first-principles study

Improving the hydrogen storage performance of carbon-based materials via transition metals incorporation has been proved experimentally, where control over the hydrogen adsorption kinetics and hydrogen surface diffusion is the key. In this work, we proved theoretically via density functional theory (DFT) how such incorporation promotes better hydrogen storage performance in Ni-based materials supported on graphene, in which static and dynamic behavior of the system were modeled by plane-wave DFT and ab initio molecular dynamics (AIMD), respectively. In addition, the hydrogen storage materials Ni10Al3 and Ni13 supported on graphene, denoted as Ni10Al3/GP and Ni13/GP, are modeled to realize the experimental observation on Ni3Al alloy under high hydrogen pressure. It was found that the Ni10Al3/GP alloy system exhibited better properties in twofold: (1) increased hydrogen adsorption capacity through providing an additional site for H2 molecular adsorption, particularly on the Al atoms, and (2) enhanced hydrogen desorption at ambient conditions observed from reversible H2 adsorption at all coverages with barrierless migration energy. Therefore, the proof from the DFT point-of-view provides valuable insight into exploring other metal alloy systems that can provide additional sites for molecular hydrogen adsorption and improve hydrogen adsorbate mobility.

Effect of Metal Carbides on Hydrogen Embrittlement: A Density Functional Theory Study

This study uses plane wave density functional theory (DFT) to investigate the effect of certain metal carbides (Niobium carbide, Vanadium carbide, Titanium carbide, and Manganese sulfide) on hydrogen embrittlement in pipeline steels. Our results predict that the interaction of hydrogen molecules with these metal carbides occurs in the long range with binding energy varying in the energy window [0.043 eV to 0.70 eV].In addition, our study shows the desorption of H2 molecules from these metal carbides in the chemisorptions. Since atomic state hydrogen interacts with NbC, VC, TiC, and MnS to cause embrittlement, we classified the strength of the hydrogen trapping as TiC + H > VC + H > NbC + H> MnS + H. In addition, our study reveals that the carbon site is a more favorable hydrogen-trapping site than the metal one.