An empirical potential for simulating hydrogen isotope retention in highly irradiated tungsten.

We describe the parameterization of a tungsten-hydrogen empirical potential designed for use with large-scale molecular dynamics simulations of highly irradiated tungsten containing hydrogen isotope atoms, and report test results. Particular attention has been paid to getting good elastic properties, including the relaxation volumes of small defect clusters, and to the interaction energy between hydrogen isotopes and typical irradiation-induced defects in tungsten. We conclude that the energy ordering of defects changes with the ratio of H atoms to point defects, indicating that this potential is suitable for exploring mechanisms of trap mutation, including vacancy loop to plate-like void transformations.

A comparative study of receptor interactions between SARS-CoV and SARS-CoV-2 from molecular modeling.

The pandemic of COVID-19 severe acute respiratory syndrome, which was fatal for millions of people worldwide, triggered the race to understand in detail the molecular mechanisms of this disease. In this work, the differences of interactions between the SARS-CoV/SARS-CoV-2 Receptor binding domain (RBD) and the human Angiotensin Converting Enzyme 2 (ACE2) receptor were studied using in silico tools. Our results show that SARS-CoV-2 RBD is more stable and forms more interactions with ACE2 than SARS-CoV.

Effect of axial molecules and linker length on CO adsorption and selectivity of CAU-8: a combined DFT and GCMC simulation study.

Density Functional Theory (DFT) and Grand Canonical Monte Carlo (GCMC) calculations are performed to study the structures and carbon dioxide (CO) adsorption properties of the newly designed metal-organic framework based on the CAU-8 (CAU stands for Christian-Albrechts Universität) prototype. In the new MOFs, the 4,4'-benzophenonedicarboxylic acid (HBPDC) linker of CAU-8 is substituted by 4,4'-oxalylbis(azanediyl)dibenzoic acid (HODA) and 4,4'-teraphthaloylbis(azanediyl)dibenzoic acid (HTDA) containing amide groups (-CO-NH- motif). Furthermore, MgO octahedral chains where dimethyl sulfoxide (DMSO) decorating the axial position bridged two Mg ions are considered.

Hydrogen adsorption mechanism of MOF-74 metal-organic frameworks: an insight from first principles calculations.

The microscopic mechanism of the H adsorption of two Mg-MOF-74 isoreticular frameworks, one with a benzenedicarboxylate (BDC) linker and the other with a dihydroxyfumarate (DHF) linker, were studied on the basis of density functional theory (DFT) method. Possible adsorption sites on the internal surface of the two MOFs were detected using molecular dynamics (AIMD) annealing simulations. The simulations were able to reproduce all adsorption sites which have been experimentally observed for the BDC-based M-MOF-74 frameworks with M = Ni and Zn.

Chemical short-range order in derivative Cr-Ta-Ti-V-W high entropy alloys from the first-principles thermodynamic study.

The development of high-entropy alloys (HEAs) focuses on exploring compositional regions in multi-component systems with all alloy elements in equal or near-equal atomic concentrations. Initially it was based on the main idea that high mixing configurational entropy contributions to the alloy free energy could promote the formation of a single solid solution phase. By using the ab-initio based Cluster Expansion (CE) Hamiltonian model constructed for the quinary bcc Cr-Ta-Ti-V-W system in combination with Monte Carlo (MC) simulations, we show that the phase stability and chemical short-range order (SRO) of the equiatomic quinary and five sub-quaternary systems, as well as their derivative alloys, can dramatically change the order-disorder transition temperatures (ODTT) as a function of alloy compositions.

The electronic structures and magnetic properties of mixed-valence Fe-based metal-organic VNU-15 frameworks: a theoretical study from linear response DFT+U calculations.

The crystal symmetries, electronic structures, and magnetic properties of metal-organic VNU-15 frameworks (VNU = Vietnam National University) were investigated using density functional calculations (DFT) with an on-site Coulomb repulsion approximation, , of 4.30 eV, determined the linear response method. Two different orientations of dimethylammonium (DMA) cations in VNU-15 were investigated.

Quantum de-trapping and transport of heavy defects in tungsten.

The diffusion of defects in crystalline materials controls macroscopic behaviour of a wide range of processes, including alloying, precipitation, phase transformation and creep. In real materials, intrinsic defects are unavoidably bound to static trapping centres such as impurity atoms, meaning that their diffusion is dominated by de-trapping processes. It is generally believed that de-trapping occurs only by thermal activation.

Mechano-chemical stability and water effect on gas selectivity in mixed-metal zeolitic imidazolate frameworks: a systematic investigation from van der Waals corrected density functional theory.

A series of Zn/Cu Zeolitic Imidazolate Frameworks (ZIFs) ZIF-202, -203, and -204 are systematically investigated by Density Functional Theory (DFT) with and without van der Waals (vdW) corrections. The elastic constants for non-solvent structures indicate that ZIF-202 and -204 are mechanically stable while ZIF-203 is unstable, which arises from the stiffness along the x-axis under a uniaxial strain in the PBE-D3 method. By considering the presence of solvents in ZIF-203, a structural phase transformation from a monoclinic to a triclinic structure is found which could be explained by the Jahn-Teller distortion.

Electron delocalization in single-layer phthalocyanine-based covalent organic frameworks: a first principle study.

In this work, we first investigate the localized electronic states in the band structures of three single-layer COFs based on typical building units of COFs chemistry. Our results confirm that the polar nature of strong bonds in these building units is a hindrance to a fully delocalized structure and disfavors the band-like mechanism of transport. We then show that a rational design of the building units can lead to dispersive band states in the electronic structure and results in conducting single-layer COFs.

Configurational Entropy in Multicomponent Alloys: Matrix Formulation from Ab Initio Based Hamiltonian and Application to the FCC Cr-Fe-Mn-Ni System.

Configuration entropy is believed to stabilize disordered solid solution phases in multicomponent systems at elevated temperatures over intermetallic compounds by lowering the Gibbs free energy. Traditionally, the increment of configuration entropy with temperature was computed by time-consuming thermodynamic integration methods. In this work, a new formalism based on a hybrid combination of the Cluster Expansion (CE) Hamiltonian and Monte Carlo simulations is developed to predict the configuration entropy as a function of temperature from multi-body cluster probability in a multi-component system with arbitrary average composition.

Monitoring Mechanical, Electronic, and Catalytic Trends in a Titanium Metal Organic Framework Under the Influence of Guest-Molecule Encapsulation Using Density Functional Theory.

In this study, we conduct a density functional theory investigation to study the mechanical stability of a titanium-based metal organic framework (MOF-901), which was hypothetically assumed to possess 2D characteristics. It is systematically found that the encapsulation of methanol enhances the mechanical stability of MOF-901 as the elastic tensors C of MOF-901∙nMeOH are higher than the corresponding C quantities reported for solvent-free MOF-901. Moreover, the 2D characteristics of MOF-901 is confirmed by verifying the negative values of C.

The Effect of Electronic Structure on the Phases Present in High Entropy Alloys.

Multicomponent systems, termed High Entropy Alloys (HEAs), with predominantly single solid solution phases are a current area of focus in alloy development. Although different empirical rules have been introduced to understand phase formation and determine what the dominant phases may be in these systems, experimental investigation has revealed that in many cases their structure is not a single solid solution phase, and that the rules may not accurately distinguish the stability of the phase boundaries. Here, a combined modelling and experimental approach that looks into the electronic structure is proposed to improve accuracy of the predictions of the majority phase.

First-principles modeling of 3d-transition-metal-atom adsorption on silicene: a linear-response DFT + U approach.

By employing DFT  +  U calculations with the linear response method, we investigate the interactions between various 3d transition-metal atoms (Cr, Mn, Fe, Co) and silicene. In the cases of two-dimensional (2D) FeSi2 and CoSi2, the metal atoms tend to penetrate into the silicene layer. While CoSi2 is non-magnetic, FeSi2 exhibits a total magnetic moment of 2.

First-principles modeling of C60-Cr-graphene nanostructures for supporting metal clusters.

We present a first-principles modeling study of a new class of nanomaterials in which buckminsterfullerene (C60) and graphene (G) are bridged by Cr via coordination bonds. Two nanostructures denoted as G(C54)-Cr-C60 and G(C150)-Cr-C60 are investigated, which share many similarities in the configuration geometries but differ in the distribution densities of Cr-C60 on the graphene surface. The binding energies between C60 and the rest of the system in these complexes are calculated to be 2.

Anatase-rutile phase transformation of titanium dioxide bulk material: a DFT + U approach.

The anatase-rutile phase transformation of TiO(2) bulk material is investigated using a density functional theory (DFT) approach in this study. According to the calculations employing the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional with the Vanderbilt ultrasoft pseudopotential, it is suggested that the anatase phase is more energetically stable than rutile, which is in variance with the experimental observations. Consequently, the DFT + U method is employed in order to predict the correct structural stability in titania from electronic-structure-based total energy calculations.

Origin of brittle cleavage in iridium.

Iridium is unique among the face-centered cubic metals in that it undergoes brittle cleavage after a period of plastic deformation under tensile stress. Atomistic simulation using a quantum-mechanically derived bond-order potential shows that in iridium, two core structures for the screw dislocation are possible: a glissile planar core and a metastable nonplanar core. Transformation between the two core structures is athermal and leads to exceptionally high rates of cross slip during plastic deformation.