First-Principles Simulation—Nano-Theory

We have investigated the structural, electronic and magnetic properties of the Mott insulator Ca₂RuO₄ under the application of a static external electric field in two regimes: bulk systems at small fields and thin films at large electric fields. Ca₂RuO₄ presents S- and L-Pbca phases with short and long c lattice constants and with large and small band gaps, respectively. Using density functional perturbation theory, we have calculated the Born effective charges as response functions. Once we break the inversion symmetry by off-centering the Ru atoms, we calculate the piezoelectric properties of the system that suggest an elongation of the system under an electric field. Finally, we investigated a four-unit cell slab in larger electric fields, and we found insulator–metal transitions induced by the electric field. By looking at the local density of states, we have found that the gap gets closed on surface layers while the rest of the sample is insulating. Correlated to the electric-field-driven gap closure, there is an increase in the lattice constant c. Regarding the magnetic properties, we have identified two phase transitions in the magnetic moments with one surface that gets completely demagnetized at the largest field investigated. In all cases, the static electric field increases the lattice constant c and reduces the band gap of Ca₂RuO₄, playing a role in the competition between the L-phase and the S-phase. Full article

A study is carried out which investigates the effects of the mono-vacancies of boron (VB) and nitrogen (VN) and the co-vacancies of nitrogen (N), and boron (B) on the energetics and the structural, electronic, and magnetic properties of an h-BN/graphene heterobilayer using first-principles calculations within the framework of the density functional theory (DFT). The heterobilayer is modelled using the periodic slab scheme. In the present case, a 4 × 4-(h-BN) monolayer is coupled to a 4 × 4-graphene monolayer, with a mismatch of 1.40%. In this coupling, the surface of interest is the 4 × 4-(h-BN) monolayer; the 4 × 4-graphene only represents the substrate that supports the 4 × 4-(h-BN) monolayer. From the calculations of the energy of formation of the 4 × 4-(h-BN)/4 × 4-graphene heterobilayer, with and without defects, it is established that, in both cases, the heterobilayers are energetically stable, from which it is inferred that these heterobilayers can be grown in the experiment. The formation of a mono-vacancy of boron (1 V_B), a mono-vacancy of nitrogen (1 V_N), and co-vacancies of boron and nitrogen (V_BN) induce, on the structural level: (a) for 1 V_B, a contraction n of the B-N bond lengths of ~2.46% and a slight change in the interfacial distance D (~0.096%) with respect to the heterobilayer free of defects (FD) are observed; (b) for 1 V_N, a slight contraction of the B-N of bond lengths of ~0.67% and an approach between the h-BN monolayer and the graphene of ~3.83% with respect to the FD heterobilayer are observed; (c) for V_BN, it can be seen that the N-N and B-B bond lengths (in the 1 V_B and 1 V_N regions, respectively) undergo an increase of ~2.00% and a decrease of ~3.83%, respectively. The calculations of the Löwdin charge for the FD heterobilayer and for those with defects (1 V_B, 1 V_N, and V_BN) show that the inclusion of this type of defect induces significant changes in the Löwdin charge redistribution of the neighboring atoms of VB and VN, causing chemically active regions that could favor the interaction of the heterobilayer with external atoms and/or molecules. On the basis of an analysis of the densities of states and the band structures, it is established that the heterobilayer with 1 V_B and V_BN take on a half-metallic and magnetic behavior. Due to all of these properties, the FD heterobilayer and those with 1 V_B, 1 V_N, and V_BN are candidates for possible adsorbent materials and possible materials that could be used for different spintronic applications. Full article

In situ X-ray crystallography powder diffraction studies on beta silicon carbide (3C-SiC) in the temperature range 25–800 °C at the maximum peak (111) are reported. At 25 °C, it was found that the lattice parameter is 4.596 Å, and coefficient thermal expansion (CTE) is 2.4 ×${10}^{-6}$/°C. The coefficient of thermal expansion along a-direction was established to follow a second order polynomial relationship with temperature $({\alpha }_{11}=-1.423\times {10}^{-12}{T}^2+4.973\times {10}^{-9}T+2.269\times {10}^{-6}$). CASTEP codes were utilized to calculate the phonon frequency of 3C-SiC at various pressures using density function theory. Using the Gruneisen formalism, the computational coefficient of thermal expansion was found to be 2.2 ×${10}^{-6}$/°C. The novelty of this work lies in the adoption of two-step thermal expansion determination for 3C-SiC using both experimental and computational techniques. Full article

Pyrophosphate crystals have a wide array of applications in industrial and biomedical fields. However, fundamental understanding of their electronic structure, optical, and mechanical properties is still scattered and incomplete. In the present research, we report a comprehensive theoretical investigation of 21 pyrophosphates A₂M (H₂P₂O₇)₂•2H₂O with either triclinic or orthorhombic crystal structure. The molecule H₂P₂O₇ is the dominant molecular unit, whereas A = (K, Rb, NH₄, Tl), M = (Zn, Cu, Mg, Ni, Co, Mn), and H₂O stand for the cation elements, transition metals, and the water molecules, respectively. The electronic structure, interatomic bonding, partial charge distribution, optical properties, and mechanical properties are investigated by first-principles calculations based on density functional theory (DFT). Most of these 21 crystals are theoretically investigated for the first time. The calculated results show a complex interplay between A, M, H₂P₂O₇, and H₂O, resulting in either metallic, half-metallic, or semi-conducting characteristics. The novel concept of total bond order density (TBOD) is used as a single quantum mechanical metric to characterize the internal cohesion of these crystals to correlate with the calculated properties, especially the mechanical properties. This work provides a large database for pyrophosphate crystals and a road map for potential applications of a wider variety of phosphates. Full article

In this paper, first principles method was adopted to investigate the point defects, Vanadium-related defects and defect combinations (vacancy (V), substitutional (S) and/or interstitial (I)) in molybdenum β-Mo₂C and explore the use of first principles calculation data in analysing the link between different carbides and the effects of doping elements. Supercell models with different defect types were established and optimized, and the formation energy data of defects was developed. The structure evolution during the optimization process is analysed in detail to establish the main characteristics of changes and the relevant electronic properties. The data for different types of intrinsic defects and combined defects complexes was developed and key results is analysed. The results show that carbon vacancy (V_C) is stable but does not inevitably exist in pure β-Mo₂C. Interstitial site II is a very unstable position for any type of atoms (Mo, V and C), and analysis of the structure evolution shows that the atom always moves to the interface area near the interstitial site I between two layers. In particular, a C atom can expand the lattice structure when it exists between the layer interfaces. One type of the defects studied, the substitution of Mo with V (designated as ‘S_V-Mo’), is the most stable defect among all single point defects. The data for defect complexes shows that the combination of multiple S_V-Mo defects in the super cell being more stable than the combination of other defects (e.g., ‘V_Mo+I_C’, ‘S_V-Mo+V_C’). The data with increasing S_V-Mo in (Mo, V)₂C system is developed, and typical data (e.g., formation energy) for Mo-rich carbides and V carbides are correlated and the potential of the data in analysing transition of different carbides is highlighted. The relevance of using first principles calculation data in the studying of V-doping and the complex carbides (V- and Mo-rich carbides) evolution in different materials systems and future focus of continuous work is also discussed. Full article

Molecular doping is an excellent instrument to modify the electronic properties of two−dimensional materials. In our work, the structure and electronic properties of the adsorption systems of g−ZnO adsorbed by organic molecules (including Tetracyanoethylene (TCNE), Tetracyanoquinodimethane (TCNQ), and Tetrahydrofulvalene (TTF)) were investigated computationally using Density Functional Theory (DFT). The results showed that the TCNE and TCNQ, as electron receptors, doped the LUMO energy level above the valence band maximum (VBM) of the g−ZnO band structure, demonstrating effective p−type doping. The n−type doping of g−ZnO was obtained that the TTF molecules, as electron donors, doped the HOMO energy level below the conduction band minimum (CBM) of the band structure for g−ZnO. In addition, the TCNE, TCNQ, and TTF breathed additional holes or electrons into the monolayer g−ZnO, creating surface dipole moments between the g−ZnO and organic molecules, which caused work function to be adjustable, ranging from 3.871 eV to 5.260 eV. Our results prove that organic molecular doping was instrumental in improving the performance of g−ZnO−based nano−electronic devices, providing theoretical support for the fabrication of p−doping or n−doping nano−semiconductor components. The tunable range of field emission capability of g−ZnO−based electronic devices was also extended. Full article

HfO₂ shows different polymorphs, including monoclinic and orthorhombic ones, that exhibit singular properties. Moreover, the character of HfO₂ is also influenced by the Zr atoms as a doping agent. Here, an extensive study of the monoclinic P2₁/c and the orthorhombic Pca2₁ polymorphs of HfO₂, Hf_0.75Zr_0.25O₂, and Hf_0.5Zr_0.5O₂ is reported. For all six systems, density functional theory (DFT) methods based on generalized gradient approximations (GGAs) were first used; then the GGA + U method was settled and calibrated to describe the electrical and optical properties of polymorphs and the responses to the oxygen vacancies. Zr had different effects in relation to the polymorph; moreover, the amount of Zr led to important differences in the optical properties of the Pca2₁ polymorph. Finally, oxygen vacancies were investigated, showing an important modulation of the properties of Hf_xZr_yO₂ nanostructures. The combined GGA and GGA + U methods adopted in this work generate a reasonable prediction of the physicochemical properties of o- and m-Hf_xZr_yO₂, identifying the effects of doping phenomena. Full article

Nitryl cyanide, O₂NCN, as a new high-energy molecule, has not yet been successfully synthesized. It has prompted us to conduct a theoretical study of its possible space structures and properties. The RESP charges and the most stable spatial structures demonstrate that crystal morphology is affected by both the main nonbonded interactions and the molecular arrangement. The crystal structure prediction indicated that there are seven structures, namely P1, P2₁, P2₁2₁2₁, P2₁/c, Pna2₁, Pbca, and C2/c. The most stable space structure is likely to be Pna2₁ and the corresponding cell parameters are Z = 4, a = 8.69 Å, b = 9.07 Å, c = 9.65 Å, and α = β = γ = 90.0°. To further study the intermolecular interactions of TNTA, a series of theoretical analyses were employed, including Hirshfeld surface analysis and fingerprint plots. The pyrolysis mechanism and properties show that high temperatures can promote decomposition. The systematic search approach can be a new strategy to identify structures effectively and has the potential to provide systematic theoretical guidance for the synthesis of TNTA. Full article

We carried out a density functional theory (DFT) study of the electronic and related properties of zinc blende indium arsenide (zb-InAs). These related properties include the total and partial densities of states and electron and hole effective masses. We utilized the local density approximation (LDA) potential of Ceperley and Alder. Instead of the conventional practice of performing self-consistent calculations with a single basis set, albeit judiciously selected, we do several self-consistent calculations with successively augmented basis sets to search for and reach the ground state of the material. As such, our calculations strictly adhere to the conditions of validity of DFT and the results are fully supported by the theory, which explains the agreement between our findings and corresponding, experimental results. Indeed, unlike some 21 previous ab initio DFT calculations that reported zb-InAs band gaps that are negative or zero, we found the room temperature measured value of 0.360 eV. It is a clear achievement to reproduce not only the locations of the peaks in the valence band density of states, but also the measured values of the electron and hole effective masses. This agreement with experimental results underscores not only the correct description of the band gap, but also of the overall structure of the bands, including their curvatures in the vicinities of the conduction band minimum (CBM) and of the valence band maximum (VBM). Full article

First principles calculations are performed to investigate the thermodynamical stability, dynamical, mechanical, electronic and magnetic properties of CrTiCoZ (Z = Al/Si) novel quaternary Heusler alloys. A Y-type III atomic configuration is found to be the most stable structure for both compounds. The lattice constant values obtained using GGA-PBE approach are 5.9368 Å and 5.7853 Å for CrTiCoAl and CrTiCoSi, respectively. Using the value of elastic moduli for both the compounds, the computed Pugh’s ratio value is 2.5 and 2.7 for CrTiCoAl and CrTiCoSi, respectively, which is higher than 1.75, indicating both the compounds are ductile in nature. The melting temperatures of both compounds are as high as 2142 K and 2420 K for CrTiCoAl and CrTiCoSi, respectively. The electronic structure calculations, using the GGA-PBE approach, show a half metallic behavior of CrTiCoAl. The spin-down channel exhibits a direct band gap of 0.15 eV, whereas the spin-up channel is metallic, making CrTiCoAl a half metallic ferromagnet with 100% spin polarization and an appreciable magnetic moment of −2 μ_B. However, CrTiCoSi is found to be semi-metallic in the spin-down channel and metallic in the spin-up channel, which leads to a spin polarization of 99.7% with a non-integer magnetic moment of −0.99 μ_B. The Curie temperature of CrTiCoAl is well above the room temperature (385 K), whereas that of CrTiCoSi is below the room temperature (203 K). Thus, CrTiCoAl is found to be more promising than CrTiCoSi as a spin injector in spintronic devices. Full article

A superatom is a cluster composed of a specific number of atoms. We recently found that the superatom-like X@Ga₁₂ (X = Li~Kr) clusters has the periodic energy levels of the specific orbitals 2S and 2P by means of the DV-Xα molecular orbital calculation method. This periodicity in energy levels has not been seen in 1D or 1F orbitals. We supposed that the periodicity of the energy levels of the 2S and 2P superatomic-like orbitals come from the same symmetry between atomic orbitals as the central atom X and the surrounding specific orbitals, according to the Jellium model. Both the s and p atomic orbitals of the central atom X in the superatom-like X@Ga₁₂ have a large shielding effect, suggesting that the s and p atomic orbitals interact strongly with both 2S and 2P superatomic-like orbitals. The energy level periodicity has the potential to periodically change the number of electrons located in the 1D and 1F orbitals, which is related to magnetic properties and is expected to be useful for novel magnetic devices by periodically controlling the magnetism of superatoms. Full article

The effects of the monovacancies of oxygen (V_O) and manganese (V_Mn) on the structural and electronic properties of the 1T–MnO₂/graphene heterostructure are investigated, within the framework of density functional theory (DFT). We found that the values of the formation energy for the heterostructure without and with vacancies of V_O and V_Mn were −20.99 $\frac{\mathrm{meV}}{{Å}^2}$, −32.11$\frac{\mathrm{meV}}{{Å}^2}$, and −20.81 $\frac{\mathrm{meV}}{{Å}^2}$, respectively. The negative values of the formation energy indicate that the three heterostructures are energetically stable and that they could be grown in the experiment (exothermic processes). Additionally, it was found that the presence of monovacancies of V_O and V_Mn in the heterostructure induce: (a) a slight decrease in the interlayer separation distance in the 1T–MnO₂/graphene heterostructure of ~0.13% and ~1.41%, respectively, and (b) a contraction of the (Mn−O) bond length of the neighboring atoms of the V_O and V_Mn monovacancies of ~2.34% and ~6.83%, respectively. Calculations of the Bader charge for the heterostructure without and with V_O and V_Mn monovacancies show that these monovacancies induce significant changes in the charge of the first-neighbor atoms of the V_O and V_Mn vacancies, generating chemically active sites (locales) that could favor the adsorption of external atoms and molecules. From the analysis of the density of state and the structure of the bands, we found that the graphene conserves the Dirac cone in the heterostructure with or without vacancies, while the 1T–MnO₂ monolayer in the heterostructures without and with V_O monovacancies exhibits half-metallic and magnetic behavior. These properties mainly come from the hybridization of the 3d–Mn and 2p–O states. In both cases, the heterostructure possesses a magnetic moment of 3.00 μ_β/Mn. From this behavior, it can be inferred the heterostructures with and without V_O monovacancies could be used in spintronics. Full article

SnP₃ has a great prospect in electronic and thermoelectric device applications due to its moderate band gap, high carrier mobility, absorption coefficients, and dynamical and chemical stability. Doping in two-dimensional semiconductors is likely to display various anomalous behaviors when compared to doping in bulk semiconductors due to the significant electron confinement effect. By introducing foreign atoms from group III to VI, we can successfully modify the electronic properties of two-dimensional SnP₃. The interaction mechanism between the dopants and atoms nearby is also different from the type of doped atom. Both Sn₇BP₂₄ and Sn₇NP₂₄ systems are indirect bandgap semiconductors, while the Sn₇AlP₂₄, Sn₇GaP₂₄, Sn₇PP_24, and Sn₇AsP₂₄ systems are metallic due to the contribution of doped atoms intersecting the Fermi level. For all substitutionally doped 2D SnP₃ systems considered here, all metallic systems are nonmagnetic states. In addition, monolayer Sn₇XP₂₄ and Sn₈P₂₃Y may have long-range and local magnetic moments, respectively, because of the degree of hybridization between the dopant and its adjacent atoms. The results complement theoretical knowledge and reveal prospective applications of SnP₃-based electrical nanodevices for the future. Full article

Nanoscale radiative thermal transport between a pair of metamaterial gratings is studied within this work. The effective medium theory (EMT), a traditional method to calculate the near-field radiative heat transfer (NFRHT) between nanograting structures, does not account for the surface pattern effects of nanostructures. Here, we introduce the effective approximation NFRHT method that considers the effects of surface patterns on the NFRHT. Meanwhile, we calculate the heat flux between a pair of silica (SiO₂) nanogratings with various separation distances, lateral displacements, and grating heights with respect to one another. Numerical calculations show that when compared with the EMT method, here the effective approximation method is more suitable for analyzing the NFRHT between a pair of relatively displaced nanogratings. Furthermore, it is demonstrated that compared with the result based on the EMT method, it is possible to realize an inverse heat flux trend with respect to the nanograting height between nanogratings without modifying the vacuum gap calculated by this effective approximation NFRHT method, which verifies that the NFRHT between the side faces of gratings greatly affects the NFRHT between a pair of nanogratings. By taking advantage of this effective approximation NFRHT method, the NFRHT in complex micro/nano-electromechanical devices can be accurately predicted and analyzed. Full article

Germanene, with a wrinkled atomic layer structure and high specific surface area, showed high potential as an electrode material for supercapacitors. According to the first-principles calculation based on Density Functional Theory, the quantum capacitance of germanene could be significantly improved by introducing doping/co-doping, vacancy defects and multilayered structures. The quantum capacitance obtained enhancement as a result of the generation of localized states near the Dirac point and/or the movement of the Fermi level induced by doping and/or defects. In addition, it was found that the quantum capacitance enhanced monotonically with the increase of the defect concentration. Full article

In present work, the effects of alloying elements X (X = Zn, Zr and Ag) doping on the phase stability, elastic properties, anisotropy and Debye temperature of Al₃Li were studied by the first-principles method. Results showed that pure and doped Al₃Li can exist and be stable at 0 K. Zn and Ag elements preferentially occupy the Al sites and Zr elements tend to occupy the Li sites. All the C_ij obey the mechanical stability criteria, indicating the mechanical stability of these compounds. The overall anisotropy decreases in the following order: Al₂₃Li₈Ag > Al₃Li > Al₂₃Li₈Zn > Al₂₄Li₇Zr, which shows that the addition of Zn and Zr has a positive effect on reducing the anisotropy of Al₃Li. The shear anisotropic factors for Zn and Zr doped Al₃Li are very close to one, meaning that elastic moduli do not strongly depend on different shear planes. For pure and doped Al₃Li phase, the transverse sound velocities ν_t1 and ν_t2 among the three directions are smaller than the longitudinal sound velocity ν_l. Moreover, only the addition of Zn is beneficial to increasing the Θ_D of Al₃Li among the three elements. Full article

The effects of benzene (C₆H₆) on the radial distribution function, coordination number, spatial distribution function, physical and chemical properties such as density, viscosity, conductivity and transport properties of triethylamine hydrochloride /chloroaluminate ([Et₃NH] Cl/AlCl₃) ionic liquid were studied by first principle and molecular dynamics simulation. The stable geometry and electronic properties of benzene and ionic liquids, as well as their optimized adsorption on Cu (111) surface were obtained. The density, viscosity and conductivity obtained agreed well with the experimental values. It is found that the adsorption of cations, anions and benzene on Cu (111) surface is physical adsorption, and the adsorption capacity is [Et₃NH] > C₆H₆ > Al₂Cl₇⁻. With the increase of benzene concentration, the density of the system decreases gradually, the interaction between cations and anions gradually weakens, resulting in the decrease of viscosity, the enhancement of diffusion and the increase of conductivity. Since the diffusion and adsorption capacity of benzene are greater than that of electroactive ion of Al₂Cl₇⁻, benzene would be easier to adsorb on the protruding part of the electrode surface, so as to reduce the effective surface area of the cathode, slow down the reduction speed of Al₂Cl₇⁻ on the cathode surface and increase the over-potential, so the grain refined deposition layers can be obtained in electrodeposition. Full article

We investigated structure optimization, mechanical stability, electronic and bonding properties of the nanolaminate compounds Ti₂PbC, Zr₂PbC, and Hf₂PbC using the first-principles calculations. These structures display nanolaminated edifices where MC layers are interleaved with Pb. The calculation of formation energies, elastic moduli and phonons reveal that all MAX phase systems are exothermic, and are intrinsically and dynamically stable at zero and under pressure. The mechanical and thermal properties are reported with fundamental insights. Results of bulk modulus and shear modulus show that the investigated compounds display a remarkable hardness. The elastic constants C₁₁ and C₃₃ rise more quickly with an increase in pressure than that of other elastic constants. Electronic and bonding properties are investigated through the calculation of electronic band structure, density of states, and charge densities. Full article

Comprehensive ab initio electronic structure calculations were performed for a newly developed deep-ultraviolet (DUV) non-linear optical (NLO) crystal Ca₂B₁₀O₁₄F₆ (CBOF) using the first principle method. Fifteen point defects including interstitial, vacancy, antisite, Frenkel, and Schottky of Ca, O, F, and B atoms in CBOF were thoroughly investigated as well as their effects on the optical absorption properties. Their formation energies and the equilibrium concentrations were also calculated by ab initio total energy calculations. The growth morphology was quantitatively analyzed using the Hartman–Perdok approach. The formation energy of interstitial F (Fi) and antisite defect O_F were calculated to be approximately 0.33 eV and 0.83 eV, suggesting that they might be the dominant defects in the CBOF material. The absorption centers might be induced by the O and F vacancies (V_F, V_O), interstitial B and O (O_i, B_i), and the antisite defect O substitute of F (O_F), which might be responsible for lowering the damage threshold of CBOF. The ionic conductivity might be increased by the Ca vacancy (V_ca), and, therefore, the laser-induced damage threshold decreases. Full article

The present work introduced first-principles calculation to explore the substitution behavior of Ag atoms for Al or Ti atoms in the Ti₂AlC MAX phase ceramic. The effect of Ag substitution on supercell parameter, bonding characteristic, and stability of the Ti₂AlC was investigated. The results show that for the substitution of Ag for Al, the Al-Ti bond was replaced by a weaker Ti-Ag bond, decreasing the stability of the Ti₂AlC. However, the electrical conductivity of the Ti₂AlC was enhanced after the substitution because of the contribution of Ag 4d orbital electrons toward the density of states (DOS) at the Fermi level coupled with the filling of Ti d orbital electrons. For the substitution of Ag for Ti, new bonds, such as Ag-Al bond, Ag-C bond, Al-Al bond, Ti-Ti anti-bond, and C-C anti-bond were generated in the Ti₂AlC. The Ti-Ti anti-bond was strengthened as well as the number of C-C anti-bond was increased with increasing the substitution ratio of Ag for Ti. Similar to the substitution of Ag for Al, the stability of the Ti₂AlC also decreased because the original Al-Ti bond became weaker as well as the Ti-Ti and C-C anti-bonds were generated during the substitution of Ag for Ti. Comparing with the loss of Ti d orbital electrons, Ag 4d orbits contributed more electrons to the DOS at the Fermi level, improving the electrical conductivity of the Ti₂AlC after substitution. Based on the calculation, the substitution limit of Ag for Al or Ti was determined. At last, the substitution behavior of Ag for Al or Ti was compared to discriminate that Ag atoms would tend to preferentially substitute for Ti atoms in Ti₂AlC. The current work provides a new perspective to understand intrinsic structural characteristic and lattice stability of the Ti₂AlC MAX phase ceramic. Full article

U₃Si₂C₂ is expected to be a new nuclear fuel as a ternary compound of uranium, silicon and carbon. However, the relevant research on U₃Si₂C₂ under accident conditions is rarely reported. Hence it is necessary to explore the service behavior of the potential U-Si-C ternary nuclear fuel in extreme environments. In this work, the structural characteristics, electronic behaviors and mechanical properties of U₃Si₂C₂, such as stable crystalline structures, density of states, charge distributions, electron localization function, electronic thermal conductivity and elastic modulus under extreme high pressure are calculated by density functional theory. The calculation results show that the lattice volume sharply increases when the external stress reached 9.8 GPa. Ionic and metallic nature coexist as to the bonding characteristics of U₃Si₂C₂, and the ionic takes the dominant position in bonding. The toughness of U₃Si₂C₂ is predicted to be better compared to U₃Si₂. Our theoretical investigation may help with the application of U₃Si₂C₂-based fuel and the design of ternary uranium fuels. Full article

Asymmetric molecule strategy is considered an effective method to achieve high power conversion efficiency (PCE) of polymer solar cells (PSCs). In this paper, nine oligomers are designed by combining three new electron-deficient units (unit_A)—n1, n2, and n3—and three electron-donating units (unit_D)—D, E, and F—with their π-conjugation area extended. The relationships between symmetric/asymmetric molecule structure and the performance of the oligomers are investigated using the density functional theory (DFT) and time-dependent density functional theory (TD–DFT) calculations. The results indicate that asymmetry molecule PEn2 has the minimum dihedral angle in the angle between two planes of unit_D and unit_A among all the molecules, which exhibited the advantages of asymmetric structures in molecular stacking. The relationship of the values of ionization potentials (IP) and electron affinities (EA) along with the unit_D/unit_A π-extend are revealed. The calculated reorganization energy results also demonstrate that the asymmetric molecules PDn2 and PEn2 could better charge the extraction of the PSCs than other molecules for their lower reorganization energy of 0.180 eV and 0.181 eV, respectively. Full article

The development of novel materials has challenges besides their synthesis. Materials such as novel MXenes are difficult to probe experimentally due to their reduced size and low stability under ambient conditions. Quantum mechanics and molecular dynamics simulations have been valuable options for material properties determination. However, computational materials scientists may still have difficulty finding specific force field models for their simulations. Force fields are usually hard to parametrize, and their parameters’ determination is computationally expensive. We show the Lennard-Jones (2-body interactions) combined with the Axilrod-Teller (3-body interactions) parametrization process’ applicability for metals and new classes of materials (MXenes). Because this parametrization process is simple and computationally inexpensive, it allows users to predict materials’ behaviors under close-to-ambient conditions in molecular dynamics, independent of pre-existing potential files. Using the process described in this work, we have made the $T{i}_{2}C$ parameters set available for the first time in a peer-reviewed work. Full article

The effects of the substitution of Fe by Co or Ni on both the structure and the magnetic properties of FeB amorphous alloy were investigated using first-principle molecular dynamics. The pair distribution function, Voronoi polyhedra, and density of states of Fe_80−xTM_xB₂₀ (x = 0, 10, 20, 30, and 40 at.%, TM(Transition Metal): Co, Ni) amorphous alloys were calculated. The results show that with the increase in Co content, the saturation magnetization of Fe_80−xCo_xB₂₀ (x = 0, 10, 20, 30, and 40 at.%) amorphous alloys initially increases and then decreases upon reaching the maximum at x = 10 at.%, while for Fe_80−xNi_xB₂₀ (x = 0, 10, 20, 30, and 40 at.%), the saturation magnetization decreases monotonously with the increase in Ni content. Accordingly, for the two kinds of amorphous alloys, the obtained simulation results on the variation trends of the saturation magnetization with the change in alloy composition are in good agreement with the experimental observation. Furthermore, the relative maximum magnetic moment was recorded for Fe₇₀Co₁₀B₂₀ amorphous alloy, due to the induced increased magnetic moments of the Fe atoms surrounding the Co atom in the case of low Co dopant, as well as the increase in the exchange splitting energy caused by the enhancement of local atomic symmetry. Full article

We present the results of ab initio studies of the structural and magnetic properties of the Pd host matrix doped by Fe atoms at various concentrations. By means of the density functional theory, we deduce that iron impurities are able to initialize significant magnetization of the Pd atoms, when the impurity concentration exceeds 3 at.%. We also demonstrate that the induced magnetization depends on impurity positions in the host matrix, in particular, there is a maximum of magnetization for a uniform distribution of the iron solute. Full article

The dielectric spectra of complex biomolecules reflect the molecular heterogeneity of the proteins and are particularly important for the calculations of electrostatic (Coulomb) and electrodynamic (van der Waals) interactions in protein physics. The dielectric response of the proteins can be decomposed into different components depending on the size, structure, composition, locality, and environment of the protein in general. We present a new robust simulation method anchored in rigorous ab initio quantum mechanical calculations of explicit atomistic models, without any indeterminate parameters to compute and gain insight into the dielectric spectra of small proteins under different conditions. We implement this methodology to a polypeptide RGD-4C (1FUV) in different environments, and the SD1 domain in the spike protein of SARS-COV-2. Two peaks at 5.2–5.7 eV and 14.4–15.2 eV in the dielectric absorption spectra are observed for 1FUV and SD1 in vacuum as well as in their solvated and salted models. Full article

(1) Background: Currently, nanomaterials have been broadly used in various applications including engineering, medicine and biology. One of the carbon allotropes such as carbon nanotubes (CNTs) implemented for fabrication of nanocomposite materials due to the hypersensitivity. The combined design of nanomaterial with chitosan (CS) and CNT expands the field of exploitation from biosensing and tissue engineering to water desalination. Therefore, the penetration of CS into CNT provides a valuable insight into the interactions between CS and CNT. (2) Methods: We performed molecular dynamics simulations, applying the umbrella sampling method, in order to calculate the potential mean force between CS and CNT. (3) Results: The estimated penetration free energies showed that CS is favorable to the penetration into CNT cavities. However, the penetration nature differs depending on the CNT’s architecture. (4) Conclusions: Our finding revealed the CS penetration process into CNT with nanoscale precision. The investigation results assist in a better understanding of the nanocomposite materials based on CS-CNT. Full article