Iodine capture of a two-dimensional layered uranyl-organic framework: a combined DFT and AIMD study.

To develop nuclear energy sustainably, it is important to effectively capture radioiodine in nuclear waste. In this study, we used density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations to investigate how well the uranyl-organic framework (UOF) could capture radioiodine. We found that the uranyl center and C-N ring sites in both cluster and periodic UOF models are very attractive to the I2 molecule. The adsorption energies of the I2 molecule in the periodic UOF models are as high as -1.10 eV, which is much higher than in the cluster model. The interaction characteristics between the I2 molecule and the UOF were revealed by electronic density topological analyses. Our AIMD simulations at 300 and 600 K have confirmed that the UOF has high adsorption kinetics for I2 molecules and can effectively capture them. The UOF has a high adsorption capacity and good adsorption stability for the I2 molecule, making it a promising option for the environmentally friendly removal of radioiodine.

Transition metal single-atoms supported on hexagonal ZnIn2S4 monolayers for the hydrogen evolution reaction.

Herein, we report a series of 5d transition metal (TM) single atoms supported on ZIS as promising catalysts for the hydrogen evolution reaction using first-principles calculations. The binding behaviors of TMs with the ZIS surface in single-atom catalyst formation are analysed using the adsorption energy (Eads), partial density of states (PDOS), charge density difference (CDD), and crystal orbital Hamilton population (COHP). The TM@ZIS (TM = Ta, W, Re, Os, Ir, and Pt) shows excellent hydrogen evolution performance with the Gibbs free energy (ΔGH*) values from -0.120 to 0.128 eV. The Tafel and Heyrovsky reaction mechanisms to drive H2 formation are also identified.

High Coordination Numbers of Actinides (An) in AnC13+ Rings (An = Th and U).

An intriguingly high abundance of both ThC13+ and UC13+ cluster cations was observed in a previous mass spectrometry experiment; however, the structural identification of these cations has not yet been completed. In this study, we determined the lowest lying structures of ThC13+ and UC13+ clusters using an unbiased structural search method. The 13-coordinate planar ring configuration was the most stable for both ThC13+ and UC13+ cluster cations. The C-An bonds in ThC13+ and UC13+ show a small degree of covalency, originating from the overlap of the s, d, and f orbitals of the An atoms with C 2p orbitals of both π and σ characteristics. The infrared and electronic absorption spectra of the most favorable planar ring configurations were theoretically simulated to facilitate the identification of the molecular structures in future experiments. This study provides an in-depth understanding of the experimental mass spectra.

Adsorption and diffusion of actinyls on the basal gibbsite (001) surface: a theoretical perspective.

Actinides are an important component of nuclear fuel for nuclear power and affect human health, and a key process in the transport of radionuclides in the environment is adsorption on mineral surfaces. In this work, we have used density functional theory (DFT) to investigate the microscopic adsorption and diffusion mechanisms of actinyls, U(V), U(VI), Np(V), Np(VI) Pu(V), and Pu(VI), on the gibbsite (001) surface. Actinyls(VI) are attached to the gibbsite surface through two An-Os bonds, which results in a bidentate inner sphere mode, while actinyls(V) favor a monodentate inner sphere adsorption mode with the gibbsite (001) surface. The solvent effects were considered through an explicit water cluster model. All the actinyls studied can be efficiently adsorbed on the gibbsite (001) surface with binding energies ranging from -113.9 kJ mol-1 to -341.2 kJ mol-1. Electronic structure analyses indicate that the cooperation of the An-Os bonds and hydrogen bonds leads to high adsorption stability of the actinyls with the gibbsite surface. The diffusion barriers of the actinyls on the gibbsite surface were determined, and the high energy barriers indicate that this type of gas-phase diffusion process is not likely to take place.

Screening out the Transition Metal Single Atom Supported on Onion-like Carbon (OLC) for the Hydrogen Evolution Reaction.

A recent experiment has confirmed that onion-like nanospheres of carbon (OLC) covered with single Pt atoms show comparable hydrogen evolution reaction (HER) catalytic activity to the commercial Pt/C. In this work, we have performed screening calculations on the single transition metal (TM) atom supported on OLC (a total of 26 candidates) using the density functional theory (DFT) to find excellent HER catalysts. Our calculated results indicate that the Nb1/CLO, Mo1/CLO, Ru1/CLO, Rh1/CLO, Pd1/CLO, and Ir1/OLC show high-efficient catalysts performance for the HER, as experimental Pt1/OLC does. We also try to seek an appropriate descriptor relevant to the Gibbs free energies, and the average local ionization energy (ALIE), which is first used to predict HER activity, shows a perfect linear correlation with Gibbs free energy. It is interesting to note that the ALIE descriptor is more successful than the commonly used d-band center.

The strong interaction of actinyl ions with fullerenol driven by multiple hydrogen bonds.

The removal of actinides from radioactive wastewater is an important subject with the continuous application of nuclear energy. All-electron density functional theory (DFT) calculations were carried out to understand the adsorption behaviors of actinyl ions on C60(OH)24 fullerenol in this work. The outer-sphere (OS) bonding mode is more stable than the inner-sphere one because of the formation of multiple hydrogen bonds in the OS mode. The actinyl(VI) ions can be more efficiently absorbed by fullerenol than actinyl(V) ones. The bonding nature of actinyl ions with C60(OH)24 was revealed by various electron density topological analyses. Multiple hydrogen bonds formed in the OS complexes show moderate bond strength with partial covalent nature and are responsible for their high stability. IR spectra were fingerprinted to distinguish the interaction modes of actinyl ions with C60(OH)24.

Highly Thermally Conductive Graphene-Based Thermal Interface Materials with a Bilayer Structure for Central Processing Unit Cooling.

Innovations of transistors toward miniaturization and integration aggravate heat accumulation of central processing units (CPUs). Thermal interface materials (TIMs) are critical to remove the generated heat and to guarantee the device reliability. Herein, maltose-assisted mechanochemical exfoliation was proposed to prepare maltose-g-graphene as a structural motif of TIMs. Then, maltose-g-graphene/gelatin composite films with a bilayer structure were prepared by two-step vacuum filtration to construct effective thermally conductive pathways consisting of the directionally arranged and tightly packed maltose-g-graphene. The bilayer composite film exhibited a remarkable in-plane thermal conductivity (30.8 W m-1 K-1) and strong anisotropic ratio (∼8325%) at 40 wt % maltose-g-graphene addition. More intriguingly, the cooling effect on CPUs was significantly better for the bilayer composite films than commercial thermal pads as TIMs. The outstanding thermally conductive stability in resistance to instantaneous and prolonged thermal shocks as well as fatigue stability was gathered. Our work offers a valuable reference to design and fabricate high-performance TIMs for CPU cooling to surmount harsh application scenarios.

First-principle study on monolayer and bilayer SnP3 sheets as the potential sensors for NO2, NO, and NH3 detection.

Layered SnP3 sheets have recently been predicted as interesting 2D material with many potential applications. In the present work, first-principles calculations were performed to investigate the possibility of layered SnP3 sheets as a candidate for detecting pollutant gases (CO, CO2, H2S, NH3, NO, and NO2). Our results indicate that CO, CO2, H2S molecules are all physisorbed on SnP3 sheets with an adsorption energy of 0.116-0.363 eV. On the other hand, the strong interactions of NH3, NO, and NO2 and SnP3 are found based on the moderate adsorption energy (around 1 eV for NO2) and large charge transfer. The monolayer SnP3 shows a higher affinity to these molecules than bilayer one. The chemisorption of NH3, NO, and NO2 molecules on layered SnP3 sheets could efficiently evoke the electrical signal, and show short recovery time for NH3, NO, and NO2 capture. The work function calculations exhibit significant responses to the NH3 and NO2 molecules. Our results proposed that SnP3 sheets could be utilized as a gas sensor for NO, NO2, and NH3, and extend the potential applications of 2D SnP3 sheets.

Atomistic investigation on effect of Ca doping ratio on mechanical behaviors of nanocrystalline Mg-Ca alloys.

The effects of doping ratio of calcium (Ca) on mechanical behaviors are investigated using molecular dynamics (MD) and the second nearest-neighbor modified embedded-atom method (2NN-MEAM) formalism for nanocrystalline (NC) Mg-Ca alloys system. Research results indicate that mechanical behaviors of Mg-Ca alloys are independent of lower strain rate (under 1.0 × 109 s-1). In addition, we observe that Ca doping can affect the mechanical properties of the Mg-Ca alloys, and the optimal 2.0 at% of Ca atoms, which has excellent plasticity, is revealed. When the doping ratio is lower than critical atomic percent (CAT) of Mg2Ca, Young's modulus and yield stress decrease increasing at% of substitutional Ca. The pyramidal dislocations are observed frequently at more active grain boundary (GB) with higher Ca doping ratios. In contrast, with doping ratio above CAT, Mg2Ca reinforcement dominates brittleness Mg/Mg2Ca nanocomposites to obtain high strength. By calculating, a significant increase of strength is discovered when at% of Mg2Ca is above 18.85 (5.34 at% Ca). Intergranular fractures are more likely to nucleate and propagate along weaker Mg/Mg2Ca interfaces. These results are instrumental in design and improving the mechanical properties of Mg-Ca alloys.

Adsorption of actinide ion complexes on C60O: An all-electron ZORA-DFT-D3 study.

All-electron DFT study was performed to understand the structures, binding natures and spectra of actinide ions complexes (Np(V), Pu(V) and Pu(VI)) adsorbed on C60O surface. The stabilities of the outer-sphere complexes are comparable with the inner-sphere complexes due to the existence of hydrogen bonding. The Pu(VI) ion complex can be more efficiently absorbed on C60O relative to other studied complexes, Np(V) and Pu(V). The bonding natures in the studied complexes were revealed with quantum theory of atoms in molecules (QTAIM), independent gradient model (IGM) and noncovalent interaction (NCI) analyses. The hydrogen bonding can be clearly found in the infrared spectra of the outer-sphere complexes, which can help us to distinguish the complex modes of actinide ion complexes with C60O.

Hydrogen storage of Li4&B36 cluster.

The Saturn-like charge-transfer complex Li4&B36, which was recently predicted with extensive first-principles theory calculations, were studied as a candidate for hydrogen storage material in the present work. The bonding characters of Li-B, B-B and Li-H2 bonds were revealed by the quantum theory of atoms in molecules (QTAIM). Each Li atom in Li4&B36 cluster can bind six H2 molecules at most, which results into the gravimetric density of 10.4%. The adsorption energies of H2 molecules on Li4&B36 cluster are predicted in the range of 0.08-0.14 eV at the wB97x level of theory.

A Systematic Theoretical Study of UC6: Structure, Bonding Nature, and Spectroscopy.

The study of uranium carbides has received renewed attention in recent years due to the potential use of these compounds as fuels in new generations of nuclear reactors. The isomers of the UC6 cluster were determined by DFT and ab initio methods. The structures obtained using SC-RECP for U were generally consistent with those obtained using an all-electron basis set (ZORA-SARC). The CCSD(T) calculations indicated that two isomers had similar energies and may coexist in laser evaporation experiments. The nature of the U-C bonds in the different isomers was examined via a topological analysis of the electron density, and the results indicated that the U-C bonds are predominantly closed-shell (ionic) interactions with a certain degree of covalent character in all cases, particularly in the linear species. The IR and UV-vis spectra of the isomers were theoretically simulated to provide information that can be used to identify the isomers of UC6 in future experiments.

Adsorption of 5f-electron atoms (ThCm) on graphene surface: An all-electron ZORA-DFT study.

All-electron calculations were performed to investigate the adsorption of 5f-electron atoms (An=ThCm) on graphene surface. The hollow site is energetically preferred for the An-graphene complexes studied. The interaction strengths between An and C decrease in the order of Th>Pa>U>Np>Pu>Cm>Am. The AnC interactions show predominately closed-shell characteristics, meanwhile ThC chemical bond formed through orbital overlaps of Th (6d) and C (2p) possesses partial covalent nature. The participation of 6d(5f)-electron into bonding orbitals are gradually weakened (enhanced) from Th to Pu because the 5f electrons are more and more diffuse. The physisorption nature of Am on graphene was observed by the weak orbital overlaps between Am (6d) and C(2p) and the half-fill 5f occupancy. The magnetic moments of An-graphene species are mainly derived from the 5f-electron due to its high delocalization. The molecular orbital (MO) and charge decomposition analysis (CDA) indicate that the 6d orbitals of An atoms play a more important role in participation of bonds relative to the 5f orbital, as well as the strong linear correlation between 6d occupancy numbers and adsorption energy highlights the significant role of 6d-electron of An in the interaction.

Exploring the Interaction Natures in Plutonyl (VI) Complexes with Topological Analyses of Electron Density.

The interaction natures between Pu and different ligands in several plutonyl (VI) complexes are investigated by performing topological analyses of electron density. The geometrical structures in both gaseous and aqueous phases are obtained with B3LYP functional, and are generally in agreement with available theoretical and experimental results when combined with all-electron segmented all-electron relativistic contracted (SARC) basis set. The Pu- O y l bond orders show significant linear dependence on bond length and the charge of oxygen atoms in plutonyl moiety. The closed-shell interactions were identified for Pu-Ligand bonds in most complexes with quantum theory of atoms in molecules (QTAIM) analyses. Meanwhile, we found that some Pu-Ligand bonds, like Pu-OH(-), show weak covalent. The interactive nature of Pu-ligand bonds were revealed based on the interaction quantum atom (IQA) energy decomposition approach, and our results indicate that all Pu-Ligand interactions is dominated by the electrostatic attraction interaction as expected. Meanwhile it is also important to note that the quantum mechanical exchange-correlation contributions can not be ignored. By means of the non-covalent interaction (NCI) approach it has been found that some weak and repulsion interactions existed in plutonyl(VI) complexes, which can not be distinguished by QTAIM, can be successfully identified.

An icosahedral Ta12(2+) cluster with spherical aromaticity.

A high-stability icosahedral cluster (Ta12(2+)) with spherical aromaticity was found within a DFT framework. The spherical aromaticity of the icosahedral Ta12(2+) cluster was confirmed by a high symmetry, a short bond length, a high vibrational frequency, a large HOMO-LUMO gap and negative NICS(0) values. The icosahedral Ta12(2+) cluster is the first example of a bare metal cluster with a total of 58 valence electrons. The electron density topological analyses (QTAIM and ELF) indicate that three-center shared interactions exist in the icosahedral structure. The IR and absorption spectra were theoretically simulated as a convenient way to confirm the existence of the icosahedral structure in further experiments.

Geometric transition and electronic properties of titanium-doped aluminum clusters: Al(n)Ti (n = 2-24).

Equilibrium geometries of AlnTi (n = 2-24) clusters were studied using density-functional theory with generalized gradient approximation. The resulting geometries showed that the titanium atom remains on the surface of clusters for n < 20 but is endohedrally doped from n = 20. This structural transition confirms the previous experiment results obtained by studying their abilities for argon physisorption (Lang, S. M.; Claes, P.; Neukermans, S.; Janssens, E. J. Am. Soc. Mass Spectrom.2011, 22, 1508). The average bond lengths, coordination numbers, relative stabilities, electronic properties, and other relevant properties were discussed. It was found that the doped titanium atoms strengthen the stabilities of the pure aluminum clusters. The coordination numbers of titanium atoms along with the average Al-Ti bond lengths undergo dramatic increases during the structural transition. The intra-atomic hybridization exists in both Ti and Al atoms, and charge transfer from Al atoms to Ti atom were found in these complexes, which should reflect the strength of Al-Ti interactions. Electronic structure analysis based on the partial density of states reveals stronger Al-Ti interactions for the endohedrally doped structures.

A theoretical study on Ta(n)+ cluster cations: structural assignments, stability, and electronic properties.

The low-lying structures of tantalum cluster cations up to n = 16 are investigated using hybrid HF/density functional theory (DFT) functionals (B3P86) in conjunction with relativistic effective core potential and corresponding basis set. The vibrational spectra of tantalum cluster cations are simulated with one empirical scaling factor of 0.943, and compared to the experimental ones [P. Gruene, A. Fielicke, G. Meijer, J. Chem. Phys. 127, 234307 (2007)]. By assigning the vibrational peaks of experimental spectra, the favored geometries actually existing in the molecular beam are obtained for several studied clusters. Based on the favored geometries, the relative stabilities, spin magnetic moments, and electronic dipole moments are determined. Furthermore, spin-related indices (ω(s) (±)) are computed and found to be good linear correlation with vertical lower-upper energy gap.

A theoretical study on small iridium clusters: structural evolution, electronic and magnetic properties, and reactivity predictors.

The structural, electronic, and magnetic properties of iridium clusters with sizes of n = 2-15 are investigated by employing the generalized gradient approximation of density functional theory. Simple cube evolution pattern is revealed for Ir(2-15) clusters, as predicted by previous reports. It is remarkable that for Ir(10), Ir(11) clusters, new generated isomers with higher stabilities relative to those reported in previous studies are obtained. The even-sized clusters are more stable than the odd-sized species. The Ir-Ir bonds in the cubic Ir(8) and Ir(12) clusters, which are considered as the basic units in the structural evolution present covalent character. Starting from n = 8, the magnetic moments of Ir(n) clusters decrease sharply. The moments of magnetic clusters show 5d characters. The reactive site selectivity of studied clusters with n = 5-15 is analyzed with condensed Fukui function. The capped atoms in certain clusters (Ir(9), Ir(10), Ir(11), and Ir(13)) generally show extraordinary activity for both nucleophilic and electrophilic attack.

Geometrical and electronic structures of small W(n) (n = 2-16) clusters.

The geometrical and electronic structures of W(n) (n=2-16) clusters are investigated within the framework of a gradient-corrected density functional theory. The close-packed configurations are preferred for small tungsten clusters up to n=16. The most energetic favorable structures of W(14), W(15), and W(16) clusters, exhibiting similar electronic band structures, are all formed based on body centered cubic (bcc) unit. The clusters with size of n=8, 12, and 15 are found to be more stable with respect to their respective neighbors. The analyses of atomic orbit projected density of states and highest occupied molecular orbital, lowest unoccupied molecular orbital isosurfaces indicate that 5d electrons play a dominant role in the chemical activities of tungsten clusters. The clearly s-d hybridizations are primary presented in bonding W atoms of smaller clusters, as the cluster sizes increase, the 6p orbitals are gradually involved in chemical bonding. Our calculated vertical ionization potentials (VIPs) indicate that the W(8) and W(12) clusters correspond to the high VIPs. The vertical electron affinities are slightly underestimated in our investigation, but follow the trends of experimental data in principle.