Ab Initio Molecular Calculations Research Articles

Large perpendicular magnetic anisotropy, high curie temperature, and half-metallicity in monolayer CrSI induced by substitution doping

The experimental discovery of two-dimensional (2D) intrinsic ferromagnets have sparked intense interest due to their potential applications in spintronics. However, the small magnetic anisotropy and low Curie temperature (TC) hinder their applications. Herein, through comprehensive first-principles calculations and Monte Carlo simulations, we investigate how Mn substitution doping affects the structure, electronic structure, magnetic properties, and TC of monolayer CrSI. Our calculations show that in contrast to ferromagnetic semiconductor with a TC of 175 K of monolayer CrSI, Mn doped monolayer CrMnS2I2 is a half-metallic ferromagnet with a TC of 312 K. Different from in-plane magnetic anisotropy of monolayer CrSI, the easy axis of monolayer CrMnS2I2 is out-of-plane, and the magnetic anisotropy of monolayer CrMnS2I2 can reach to 1.434 meV/atom, which is much larger than 0.001 meV/atom of monolayer CrSI. Additionally, the phonon dispersion, ab initio molecular dynamics simulations, formation energy, and elastic constants calculations indicate that monolayer CrMnS2I2 possesses excellent stability. Our findings provide a promising route to realize 2D intrinsic ferromagnetic half-metallic materials with a high TC and a large perpendicular magnetic anisotropy.

Structural and electronic properties of U4O9 from ab initio and empirical potential calculations

We address here the description of the different phases of ${\mathrm{U}}_{4}{\mathrm{O}}_{9}$ with ab initio density functional theory and molecular dynamics empirical potential calculations. These phases are built from the $\mathrm{U}{\mathrm{O}}_{2}$ fluorite by the addition of oxygen interstitials which assemble in clusters named cuboctahedra. Due to the unit cell size and complexity, their simulation represents a formidable task for numerical approaches. With $\mathrm{DFT}+U$, we study in detail two potential structures for $\ensuremath{\alpha}\ensuremath{-}{\mathrm{U}}_{4}{\mathrm{O}}_{9}$, however, these are just two representatives among the numerous coexisting structures we found. The role of the different valence uraniums (${\mathrm{U}}^{4+}, {\mathrm{U}}^{5+}$, and possibly ${\mathrm{U}}^{6+}$) is highlighted thanks to our quantum-mechanical approach. Temperature effects are then appraised with empirical potentials to describe the evolution of the ${\mathrm{U}}_{4}{\mathrm{O}}_{9}$ structure with temperature. We observe a continuous symmetrization of the structure with increasing temperature. Indeed, below 800 K, it gradually turns cubic and the cuboctahedral oxygen clusters tend to symmetrize. Beyond 800 K, the cuboctahedra start to disappear up to 1400 K, where none can be found in our simulated structures.

Engineering Single-Atom Electrocatalysts for Enhancing Kinetics of Acidic Volmer Reaction.

The design of active and low-cost electrocatalyst for hydrogen evolution reaction (HER) is the key to achieving a clean hydrogen energy infrastructure. The most successful design principle of hydrogen electrocatalyst is the activity volcano plot, which is based on Sabatier principle and has been used to understand the exceptional activity of noble metal and design of metal alloy catalysts. However, this application of volcano plot in designing single-atom electrocatalysts (SAEs) on nitrogen doped graphene (TM/N4C catalysts) for HER has been less successful due to the nonmetallic nature of the single metal atom site. Herein, by performing ab initio molecular dynamics simulations and free energy calculations on a series of SAEs systems (TM/N4C with TM = 3d, 4d, or 5d metals), we find that the strong charge-dipole interaction between the negatively charged *H intermediate and the interfacial H2O molecules could alter the transition path of the acidic Volmer reaction and dramatically raise its kinetic barrier, despite its favorable adsorption free energy. Such kinetic hindrance is also experimentally confirmed by electrochemical measurements. By combining the hydrogen adsorption free energy and the physics of competing interfacial interactions, we propose a unifying design principle for engineering the SAEs used for hydrogen energy conversion, which incorporates both thermodynamic and kinetic considerations and allows going beyond the activity volcano model.

A Novel BC2N Monolayer as Anode Material for Li-Ion Battery

The stability, mechanical and electronic properties of a BC2N monolayer and its potential use as an anode material for Li-ion batteries were explored using the density functional theory calculation. The proposed BC2N monolayer shows good thermal and dynamical stabilities, as indicated by the ab initio molecular dynamics simulations and phonon dispersion calculations. The BC2N monolayer exhibits highly anisotropic mechanical properties. The electronic structure calculation based on the hybrid functional suggests that the BC2N monolayer is an indirect bandgap (~1.8 eV) semiconductor. The BC2N monolayer shows linear dichroism and is able to harvest visible and ultraviolet light. To investigate the application of the BC2N monolayer as a potential anode material for Li-ion batteries, the Li adsorption and diffusion on the monolayer were studied. The BC2N monolayer exhibits a high theoretical capacity of 1098 mAh/g for Li-ion batteries. The calculated diffusion barrier of Li ion is 0.45 eV, suggesting a rapid Li-ion charge and discharge rate. The unique mechanical and optical properties of the BC2N monolayer also make it an attractive material for use in advanced nanomechanical and optoelectronic devices.

Excited-State Dynamics during Primary C-I Homolysis in Acetyl Iodide Revealed by Ultrafast Core-Level Spectroscopy.

In typical carbonyl-containing molecules, bond dissociation events follow initial excitation to nπC═O* states. However, in acetyl iodide, the iodine atom gives rise to electronic states with mixed nπC═O* and nσC-I* character, leading to complex excited-state dynamics, ultimately resulting in dissociation. Using ultrafast extreme ultraviolet (XUV) transient absorption spectroscopy and quantum chemical calculations, we present an investigation of the primary photodissociation dynamics of acetyl iodide via time-resolved spectroscopy of core-to-valence transitions of the I atom after 266 nm excitation. The probed I 4d-to-valence transitions show features that evolve on sub-100-fs time scales, reporting on excited-state wavepacket evolution during dissociation. These features subsequently evolve to yield spectral signatures corresponding to free iodine atoms in their spin-orbit ground and excited states with a branching ratio of 1.1:1 following dissociation of the C-I bond. Calculations of the valence excitation spectrum via equation-of-motion coupled cluster with single and double substitutions (EOM-CCSD) show that initial excited states are of spin-mixed character. From the initially pumped spin-mixed state, we use a combination of time-dependent density functional theory (TDDFT)-driven nonadiabatic ab initio molecular dynamics and EOM-CCSD calculations of the N4,5 edge to reveal a sharp inflection point in the transient XUV signal that corresponds to rapid C-I homolysis. By examining the molecular orbitals involved in the core-level excitations at and around this inflection point, we are able to piece together a detailed picture of C-I bond photolysis in which d → σ* transitions give way to d → p excitations as the bond dissociates. We also report theoretical predictions of short-lived, weak 4d → 5d transitions in acetyl iodide, validated by weak bleaching in the experimental transient XUV spectra. This joint experimental-theoretical effort has thus unraveled the detailed electronic structure and dynamics of a strongly spin-orbit coupled system.

Realizing the heteromorphic superlattice: Repeated heterolayers of amorphous insulator and polycrystalline semiconductor with minimal interface defects.

An unconventional "heteromorphic" superlattice (HSL) is realized, comprised of repeated layers of different materials with differing morphologies: semiconducting pc-In2 O3 layers interleaved with insulating a-MoO3 layers. Originally proposed by Tsu in 1989, yet never fully realized, the high quality of the HSL heterostructure demonstrated here validates the intuition of Tsu, whereby the flexibility of the bond angle in the amorphous phase and the passivation effect of the oxide at interfacial bonds serve to create smooth, high-mobility interfaces. The alternating amorphous layers prevent strain accumulation in the polycrystalline layers while suppressing defect propagation across the HSL. For the HSL with 7:7nm layer thickness, the observed electron mobility of 71 cm2 /Vs, matches that of the highest quality In2 O3 thin films. The atomic structure and electronic properties of crystalline In2 O3 / amorphous MoO3 interfaces are verified using ab-initio molecular dynamics simulations and hybrid functional calculations. This work generalizes the superlattice concept to an entirely new paradigm of morphological combinations. This article is protected by copyright. All rights reserved.

Revealing the interface energy and electronic properties of NbN/α-Fe in shipbuilding steels

In this work, the low index interfacial configuration, interface energy and electronic properties of the NbN/α-Fe interface in shipbuilding steels were investigated by using the first-principles method and ab initio molecular dynamics simulation calculations. Additionally, the NbN/α-Fe interface with the low index interfacial configuration was calculated by two-dimensional disregistry method. It is shown that the relaxation optimization of the NbN(001)/α-Fe(001) structure is carried out and the interfacial energy of Fe-Nb type, Fe-bridge type and Fe-C type NbC(001)/α-Fe(001) structure is calculated, the Fe-N type has an interfacial energy of −1.659 J/m2, the smallest interfacial energy and thus is the most stable. Thereby, the Fe-N type is the most stable conformation of NbN(001) /α-Fe(001). There are strong orbital resonance phenomena between Fe-3d, Nb-4d and N-2p, producing strong metallic and covalent bonds. The results of disregistry calculation by different interfacial structures of NbN/α-Fe showed that the disregistry of NbN(001)/α-Fe(001) crystalline surface was the smallest at 8.65 %, which matches well with the results of interfacial energy calculation. The results indicated that the α-Fe(001) is the optimal orientation surface of the NbN(001). This study reveals the stable bonding mode and site-oriented relationship of NbN/α-Fe interface in steel, which provides important theoretical guidance to explore the mechanism of grain refinement of NbN particles in shipbuilding steels.

Dynamic catalysis of sub-nanometer metal clusters in oxygen dissociation

When the catalyst size decreases down to the nanometer or even sub-nanometer scale, their geometric and electronic structures are very different from the bulk materials. Especially, their structural dynamics can greatly affect catalytic performances. Herein, we report a theoretical study on oxygen dissociation on Ag19 cluster, a critical step of ethylene epoxidation, to investigate the effect of structural dynamics on the catalytic activity. Combining ab initio molecular dynamics (AIMD) and free energy calculation, we obtain the free energy profiles under different temperatures and find sudden drops in the reaction free energy and barrier at certain temperature ranges. The reaction entropy change shows a positive peak because of the different melting temperatures between initial and final states. Additionally, we further investigate the oxygen diffusion process on the Ag cluster and compare it with the Au and Cu clusters. We find that weak adsorption of oxygen on the silver cluster leads to its facile diffusion and thus reduces the melting temperature of the cluster, therefore facilitating partial oxidation under mild conditions.

Role of morphology in defect formation and photo-induced carrier instabilities in amorphous indium oxide

Ab initio molecular dynamics liquid-quench simulations and hybrid density functional calculations are performed to model the effects of room-temperature atomic fluctuations and photo-illumination on the structural and electronic properties of amorphous sub-stoichiometric In2O2.96. A large configurational ensemble is employed to reliably predict the distribution of localized defects as well as their response to the thermal and light activation. The results reveal that the illumination effects on the carrier concentration are greater in amorphous configurations with shorter In–O bond length and reduced polyhedral sharing as compared to the structures with a more uniform morphology. The obtained correlation between the photo-induced carrier density and the reduction in the number of fully coordinated In-atoms implies that metal oxides with a significant fraction of crystalline/amorphous interfaces would show a more pronounced response to illumination. Photo-excitation also produces In–O2–In defects that have not been previously found in sub-stoichiometric amorphous oxides; these defects are responsible for carrier instabilities due to overdoping.

Electronic structures of zwitterionic and protonated forms of glycine betaine in water: Insights into solvent effects from ab initio simulations

Glycine betaine (GB), a naturally occurring osmolyte, has many biological functions and is used in food supplements, pharmaceuticals, and animal feed. GB usually exists as a zwitterion in aqueous solutions. Due to the hygroscopic property of GB, protonated form of GB, GBH+ (noted as GBH) is often used. In order to understand the hydration structures of GB and GBH at the atomic and electronic-structure level, a combination of ab initio molecular dynamics simulations and electronic structure calculations based on density functional theory (DFT), single-excitation configuration interaction method, and coupled-cluster ansatz was utilized. A hybrid explicit–implicit solvation model was used to elucidate solvent effects. Within the hybrid scheme, microsolvated structures of GB and GBH with up to 100 water molecules were obtained, showing that water molecules bind to GB and GBH in a dramatically different manner. By calculating the molecular electron-density distributions at PBE0-D4/def2-TZVP level, it shows that the variation of electron density for GB is more significant than GBH, suggesting that GB can interact with more water molecules than GBH. The interaction energies of GB–(H2O)n and GBH–(H2O)n systems (n = 1–6) at DLPNO-CCSD(T)/cc-pVQZ level highlight the difference from an energy point of view. Using the microsolvated structures of GB and GBH, the features of experimental K-edge spectra can be reproduced using the efficient PNO-ROCIS/B3LYP method, implying the reliability of the hybrid explicit–implicit solvation approach. The results suggest that complementary insights into the geometries and electronic structures of GB and GBH could be obtained through combined methods, which provides a methodological approach for understanding the hydration structures of zwitterionic and charged molecules.

Effect of Pressure on the Distribution of Electrons in a Cluster of H2S.

We carry out a theoretical study of the effect of pressure on the atomic and electronic distribution of a cluster made of 155 H2S molecules. The pressure was modeled by bringing the cluster into a spherical container made of 500 helium atoms and reducing the diameter of the container. We did ab initio molecular calculations using DFT. At the lowest pressure, the S-H-S angle between two neighboring H2S molecules has a distribution with a mean value of 167.1°. This angle will be shorter as pressure increases, reaching a distribution with a mean value of 125.5° at the highest pressure. Changes in this angle result from a strong S-S interaction, displacing the H atoms from the line joining the sulfur atoms. This rearrangement of the atomic distribution generates hydrogen-rich spatial regions. We analyzed the evolution of Mulliken charges on S and H atoms in the cluster with pressure, finding that electrons move from S to H atoms, suggesting that these hydrogen-rich regions should be responsible for the electrical conductivity and, consequently, also for the superconductivity in solid H2S under pressure.

Hydrogen-Induced Restructuring of a Cu(100) Electrode in Electroreduction Conditions

The rearrangement of Cu surfaces under electrochemical conditions is known to play a key role in the surface activation for major electrocatalytic reactions. Despite the extensive experimental insights into such rearrangements, from surface-sensitive spectroscopy and microscopy, the spatial and temporal resolution of these methods is insufficient to provide an atomistic picture of the electrochemical interface. Theoretical characterization has also been challenged by the diversity of restructuring configurations, surface stoichiometry, adsorbate configurations, and the effect of the electrode potential. Here, atomistic insight into the restructuring of the electrochemical interface is gained from first principles. Cu(100) restructuring under varying applied potentials and adsorbate coverages is studied by grand canonical density functional theory and global optimization techniques, as well as ab initio molecular dynamics and mechanistic calculations. We show that electroreduction conditions cause the formation of a shifted-row reconstruction on Cu(100), induced by hydrogen adsorption. The reconstruction is initiated at 1/6 ML H coverage, when the Cu-H bonding sufficiently weakens the Cu-Cu bonds between the top- and sublayer, and further stabilized at 1/3 ML when H adsorbates fill all the created 3-fold hollow sites. The simulated scanning tunneling microscopy (STM) images of the calculated reconstructed interfaces agree with experimental in situ STM. However, compared to the thermodynamic prediction, the onsets of reconstruction events in the experiment occur at more negative applied voltages. This is attributed to kinetic effects in restructuring, which we describe via different statistical models, to produce the potential- and pH-dependent surface stability diagram. This manuscript provides rich atomistic insight into surface restructuring in electroreduction conditions, which is required for the understanding and design of Cu-based materials for electrocatalytic processes. It also offers the methodology to study the problem of in situ electrode reconstruction.

Optical study of a-BaTiO3 thin films grown at different annealing temperatures

Thin films of amorphous BaTiO3 (a-BTO) were grown by spin coating technique on a glass substrate and annealed at different temperatures, from 300 to 500 °C, with a step of 50 °C. The samples were characterized structurally by X-ray diffraction (XRD), where broadband around 25° indicates the amorphous formation in all the thin films. The optical properties of the a-BTO thin films were determined by transmittance and reflectance UV-Visible spectroscopy. The optical responses were fit using Lorentz and Lorentz-Tauc classical models to determine the complex dielectric function. In addition, the photoluminescence (PL) of the glass and the a-BTO/glass system was also measured to observe the antireflective capacity of the a-BTO thin film as a function of the calcination temperature. To understand the experimental structural results ab-initio molecular dynamic calculation of 2x2x2 BTO supercell was utilized, while the electronic density of state and the complex dielectric function were obtained using Density Functional Theory (DFT). A comparison between the experimental and theoretical results is presented and discussed.

Multilevel Computational Studies Reveal the Importance of Axial Ligand for Oxygen Reduction Reaction on Fe-N-C Materials.

The systematic improvement of Fe-N-C materials for fuel cell applications has proven challenging, due in part to an incomplete atomistic understanding of the oxygen reduction reaction (ORR) under electrochemical conditions. Herein, a multilevel computational approach, which combines ab initio molecular dynamics simulations and constant potential density functional theory calculations, is used to assess proton-coupled electron transfer (PCET) processes and adsorption thermodynamics of key ORR intermediates. These calculations indicate that the potential-limiting step for ORR on Fe-N-C materials is the formation of the FeIII-OOH intermediate. They also show that an active site model with a water molecule axially ligated to the iron center throughout the catalytic cycle produces results that are consistent with the experimental measurements. In particular, reliable prediction of the ORR onset potential and the Fe(III/II) redox potential associated with the conversion of FeIII-OH to FeII and desorbed H2O requires an axial H2O co-adsorbed to the iron center. The observation of a five-coordinate rather than four-coordinate active site has significant implications for the thermodynamics and mechanism of ORR. These findings highlight the importance of solvent-substrate interactions and surface charge effects for understanding the PCET reaction mechanisms and transition-metal redox couples under realistic electrochemical conditions.

Surface-Preferred Crystal Plane Growth Enabled by Underpotential Deposited Monolayer toward Dendrite-Free Zinc Anode.

Aqueous Zn batteries with ideal energy density and absolute safety are deemed the most promising candidates for next-generation energy storage systems. Nevertheless, stubborn dendrite formation and notorious parasitic reactions on the Zn metal anode have significantly compromised the Coulombic efficiency (CE) and cycling stability, severely impeding the Zn metal batteries from being deployed in the proposed applications. Herein, instead of random growth of Zn dendrites, a guided preferential growth of planar Zn layers is accomplished via atomic-scale matching of the surface lattice between the hexagonal close-packed (hcp) Zn(002) and face-centered cubic (fcc) Cu(100) crystal planes, as well as underpotential deposition (UPD)-enabled zincophilicity. The underlying mechanism of uniform Zn plating/stripping on the Cu(100) surface is demonstrated by ab initio molecular dynamics simulations and density functional theory calculations. The results show that each Zn atom layer is driven to grow along the exposed closest packed plane (002) in hcp Zn metal with a low lattice mismatch with Cu(100), leading to compact and planar Zn deposition. In situ optical visualization inspection is adopted to monitor the dynamic morphology evolution of such planar Zn layers. With this surface texture, the Zn anode exhibits exceptional reversibility with an ultrahigh Coulombic efficiency (CE) of 99.9%. The MnO2//Zn@Cu(100) full battery delivers long cycling stability over 548 cycles and outstanding specific energy and power density (112.5 Wh kg-1 even at 9897.1 W kg-1). This work is expected to address the issues associated with Zn metal anodes and promote the development of high-energy rechargeable Zn metal batteries.

A first-principles study of structural, electronic and optical properties of α-Te tubular nanostructures modulated by uniaxial strain

First-principles calculations were performed to study the effect of uniaxial strain on the electronic properties of α-Te nanotubes (NTs) of different configurations and tube sizes. Our ab initio molecular dynamics simulation and phonon dispersion calculation indicate that both armchair (5, 5) and zigzag (10, 0) α-Te NTs are thermodynamically stable and exhibit good dynamic stability at room temperature. Under compressive and tensile strains of ±10%, the atomic structure of the α-Te NTs remains stable, demonstrating they have good flexibility. An increase in uniaxial strain leads to a progressive decrease in the band gap for both armchair and zigzag α-Te NTs. Interestingly, it is found that armchair (5, 5) α-Te NTs experience an intriguing semiconductor–metal transition at a critical strain, while other α-Te NTs are semiconducting with an adjustable band gap. In addition, the valence band maximum and conduction band minimum charge density between the interlayers has an impact on the type of band gap in the (5, 5) and (10, 0) NTs. Finally, we found the optical properties can be significantly modulated under strain in the z direction. Increasing our understanding of the electronic and optical properties of α-Te NTs under strain modulation helps shed light on the properties of new nanomaterials more generally, paving the way for future optoelectronic applications. These findings highlight the tunable electronic and optical properties of α-Te NTs, which is promising for applications in nanodevices such as opto-electronics, electrical switches, and nanoscale strain sensors.

Power of sulfur – Chemistry, properties, laser ignition and theoretical studies of energetic perchlorate-free 1,3,4-thiadiazole nitramines

The chemistry of lead-, azide- and perchlorate-free photosensitive energetic materials suitable for laser-ignition systems is an emerging field of research with a broad range of applications. To develop less toxic materials that would be sufficiently thermostable, safe, and sensitive enough to be ignited by low-power laser, is a formidable challenge. In this work, we designed, prepared, and studied properties of new sulfur-containing energetic molecules (SEMols), based on novel N-(1,3,4-thiadiazol-2-yl)nitramide explosophore. Newly synthesized energetic compounds N-(5-nitro-1,3,4-thiadiazol-2(3H)-ylidene)-nitramide (L1) and N5,N5′-dinitro-[2,2′-bi(1,3,4-thiadiazole)]-5,5′(4H,4′H)-diimine (L4) were found to be more thermostable than their sulfur-free 1,3,4-oxadiazole analogues. In small-scale detonation experiments, L1, L4, and C7 showed better brisance than TNT. Perchlorate-free complex C7 was found to have low-power laser igniting properties, showing an ignition delay time of 11 ms and threshold ignition energy of 12.0 mJ (at 915 nm irradiation). Extensive crystal-level (328-atom super-cell) ab-initio molecular dynamics and TD-DFT calculations were performed to study the laser ignition mechanism of C7. Based on our hypothesis, this photo-thermal ignition is taking place via sequential multi-photon absorption, with energy transfer to vibrational motions in this molecule. We suggest that SEMols, such as C7, can open a new platform for the development of novel energetic materials that have a potential for integration into laser-based safe energetic components in civil, aerospace, and defense applications.

X-ray absorption spectra of aqueous cellobiose: Experiment and theory

The hydration structure of cellulose is very important for understanding the hydrolysis of cellulose at the molecular level. In this paper, we report a joint experimental and theoretical study on x-ray absorption spectroscopy (XAS) of aqueous cellobiose, a disaccharide unit of cellulose. In the experimental part, high resolution measurements of the carbon K-edge XAS spectra were taken. In the theoretical part, ab initio molecular dynamics simulations and ensemble calculations of electronic excited states were performed to obtain the continuous XAS spectra. The XAS spectra were found to have three characteristic peaks at 289.3, 290.7, and 293.6eV, each representing the absorption by carbon atoms of the alcohol group, the hemiacetal group, and both of these functional groups. It was found that the peak heights in the spectrum change considerably over the temperature range of 25-60 °C, which is a reflection of the number of hydrogen bonds between cellobiose and water. We suggest that this spectral change could be useful information for identifying the hydration of cellulose in various environments.

Electronic structure of the solvated benzene radical anion

The benzene radical anion is a molecular ion pertinent to several organic reactions, including the Birch reduction of benzene in liquid ammonia. The species exhibits a dynamic Jahn-Teller effect due to its open-shell nature and undergoes pseudorotation of its geometry. Here, we characterize the complex electronic structure of this condensed-phase system based on ab initio molecular dynamics simulations and GW calculations of the benzene radical anion solvated in liquid ammonia. Using detailed analysis of the molecular and electronic structure, we find that the spatial character of the excess electron of the solvated radical anion follows the underlying Jahn-Teller distortions of the molecular geometry. We decompose the electronic density of states to isolate the contribution of the solute and to examine the response of the solvent to its presence. Our findings show the correspondence between instantaneous molecular structure and spin density; provide important insights into the electronic stability of the species, revealing that it is, indeed, a bound state in the condensed phase; and offer electronic densities of states that aid in the interpretation of experimental photoelectron spectra.

A new direct band gap Si-Ge allotrope with advanced electronic and optical properties.

Direct-band silicon materials have been a sought-after material for potential applications in silicon photonics and solar cells. Accordingly, methodologies like nanostructure engineering, alloy engineering and strain engineering have been developed. In this work, the particle swarm optimization (PSO) algorithm is used to design direct-band Si-Ge alloys. The findings of phonon computations demonstrate that all these structures are dynamically stable. In addition, ab initio molecular dynamics and elastic constant calculations are carried out, with results indicating these structures are thermodynamically stable at 300 K, as well as being mechanically stable. All of these materials exhibit semiconductor behavior with band gaps of 1.03, 0.68 and 1.37 eV for α, β and γ phases, respectively, at the HSE06 level. The results of effective mass and mobility of carriers that are important in applications show that holes are more easily transported in all structures, with higher concentration of holes accompanied by lower carrier mobility. Different concentrations of holes nh lead to different limits in the scattering process. When nh is lower than the value of around 1016 cm-3, deformation potential scattering is dominant, while the ionized impurity scattering process limits overall mobility when nh is higher than such a value. Finally, the absorption spectra shows that both α and β phases have isotropic optical properties in the X- and Y-directions while strong anisotropy can be seen in the Z-direction. However, the γ phase exhibits no notable isotropy. This investigation finds three direct-band and potentially CMOS compatible materials, a finding which will benefit the development of high efficiency emitters or solar cells.