Ab Initio Investigation Research Articles

Ab Initio investigation for DNA nucleotide bases sequencing using chiral carbon nanobelts and nanotubes

Understanding the interaction mechanism between DNA nucleotide bases and carbon nanomaterials is an important issue in the field of identifying nucleotide molecules sequencing. In this article, the adsorption behavior of DNA nucleotide bases on the external surface of chiral carbon nanobelts (CNBs) (6, 5), (7, 6) and (8, 6), was comprehensively investigated from electronic and optical perspectives. As a result, it was determined that the DNA nucleotide bases have optical absorption in the ultraviolet region. When bases are adsorbed on the surface of CNBs, the optical absorption peak of the new complex structure shifted to the visible region. The study of the optical properties of selected CNBs showed that CNB (6,5) performs better in detecting Cytosine and the red shift in the absorption spectrum of complex structure is noticeable. Also, the effect of infinite length for chiral CNTs in DNA nucleotide base sequencing was investigated using DFTB approach. Our investigations based on electronic properties showed that CNTs have better performance than CNBs in DNA nucleotide base sequencing.

Ab initio investigations on the electronic properties and stability of Cu-substituted lead apatite (LK-99) family with different doping concentrations (x = 0, 1, 2)

The pursuit of room-temperature ambient-pressure superconductivity in novel materials has sparked interest, with recent reports suggesting such properties in Cu-substituted lead apatite, known as LK-99. However, these claims lack comprehensive experimental and theoretical support. In this study, we address this gap by conducting ab initio calculations to explore the impact of varying doping concentrations (x = 0, 1, 2) on the stability and electronic properties of five compounds in the LK-99 family. Our investigations confirm the isolated flat bands that intersect the Fermi level in LK-99 (Pb9Cu(PO4)6O:Cu<Pb(1)>). In contrast, the other four parent compounds exhibit insulating behavior with wide band gaps. X-ray diffraction spectra based on the DFT simulations at 0 K confirm the presence of Cu substitution on Pb(1) sites in the originally synthesized LK-99 sample, while an extra peak suggests potential alternative like Pb8Cu2(PO4)6 phases due to compositional variations in the original LK-99 samples. Furthermore, the LK-99 structure undergoes substantial lattice constriction, resulting in a significant 5.5% reduction in volume and 6.8% in area of two mutually inverted triangles formed by Pb(2) atoms. Meanwhile, energy calculations reveal a marginal energy preference for substituting Cu on Pb(2) sites over Pb(1) sites, with a difference of approximately 0.010 eV per atom (roughly 0.9645 kJ/mol). Intriguingly, at pressures exceeding 73 GPa, stability shifts towards LK-99 containing Cu substitutions on Pb(1) sites. Despite exhibiting higher electronic conductivity than parent compounds, Pb9Cu(PO4)6O:Cu<Pb(1)> falls short of the conductivity levels observed in metals or advanced oxide conductors with the simulation based on the Boltzmann transport theory.

Ab-initio investigation of the physical properties of BaAgAs Dirac semimetal and its possible thermo-mechanical and optoelectronic applications

BaAgAs is a ternary Dirac semimetal which can be tuned across a number of topological orders. In this study we have investigated the bulk physical properties of BaAgAs using density functional theory based computations. Most of the results presented in this work are novel. The optimized structural parameters are in good agreement with previous results. The elastic constants indicate that BaAgAs is mechanically stable and brittle in nature. The compound is moderately hard and possesses fair degree of machinability. There is significant mechanical/elastic anisotropy in BaAgAs. The Debye temperature of the compound is medium and the phonon thermal conductivity and melting temperature are moderate as well. The bonding character is mixed with notable covalent contribution. The electronic band structure calculations reveal clear semimetallic behavior with a Dirac node at the Fermi level. BaAgAs has a small ellipsoidal Fermi surface centered at the Γ-point of the Brillouin zone. The phonon dispersion curves show dynamical stability. There is a clear phonon band gap between the acoustic and the optical branches. The energy dependent optical constants conform to the band structure calculations. The compound is an efficient absorber of the ultraviolet light and has potential to be used as an anti-reflection coating. Optical anisotropy of BaAgAs is moderate. The computed repulsive Coulomb pseudopotential is low indicating that the electronic correlations in this compound are not strong.

Ab initio investigation of structural, elastic, and thermodynamic characteristics of tetragonal XAgO compounds (X = Li, Na, K, Rb)

The present research utilizes ab initio computations to examine the thermodynamic, structural, and elastic characteristics of XAgO ternary oxides, where X signifies Li, Na, K, and Rb.The GGA-PBE and GGA-WC functionals were used to calculate the ground-state lattice parameters and atomic position coordinates of the title materials. The calculated results were in good agreement with both experimental measurements and theoretical predictions. This suggests that the GGA-PBE and GGA-WC functionals are accurate for describing the structural properties of the material under study.This study offers computational predictions for the elastic properties of monocrystalline structures and polycrystalline aggregates of XAgO compounds. These predictions encompass various key parameters, including single-crystal elastic constants, Young’s modulus, bulk modulus, Lame coefficients, Poisson’s ratio, shear modulus, and Debye temperature. Additionally, the quasi-harmonic Debye approximation is utilized to explore the temperature-dependent behavior of bulk modulus, Debye temperature, volume thermal expansion coefficient, and isobaric and isochoric heat capacities over an extensive temperature range, while maintaining constant pressures. The results obtained from this model are found to be highly successful in accurately predicting the behavior of these properties.

An ab-initio investigation of structural, electronic, optical and elastic properties of novel double Vacancy-ordered perovskite Cs2MoI6 for photocatalytic application

Manipulation of appropriate photocatalyst is a core issue for applications in photocatalytic degradation of contaminants. In this context, the double perovskite Cs2MoI6 exhibit encouraging photocatalytic properties, suggesting it may be useful for photocatalytic water-splitting and contaminants degradation. Here, we have analyzed the structural, electrical, optical, and elastic characteristics of Cs2MoI6 employing first-principles density functional theory computations. According to structural property studied compound is cubic with 7.75Å lattice constant. There have determined through research that the perovskite Cs2MoI6 has mechanical stability and anisotropic elastic characteristics. Upon inspection of its electronic band structure, Cs2MoI6 is originating to be a semiconductor with direct bandgap energy of 1.33eV. With a small effective mass of hole carriers and a narrow bandgap, electrons can easily move to the surface, boosting the photocatalytic rate. The formation of electron-hole pairs upon photon absorption, as predicted by the relevant band edge potential, indicates the substance's capability to splitting water into its constituent H2 and O2 molecules. Our results are predictable to subsidize the improvement of efficient photocatalytic devices for use in degradation of ecological contaminants. Based on the achieved tunable moderate bandgap and noble optical absorption in the UV region, the Cs2MoI6 proposed for utilization in various thermoelectric, electrical, optical and optical applications, particularly in novel energy generation applications.

Ab initio investigation on predissociation of the A2Σ+ state of the SeH radical induced by spin-orbit coupling

High-level ab initio calculations are performed to investigate potential energy curves (PECs) of seven low-lying Λ-S states associated with the two lowest dissociation limits of the SeH radical by utilizing the internally contracted multireference configuration interaction (icMRCI) method in combination with the aug-cc-pwCV5Z Gaussian basis set. The scalar relativistic effect (SR), the electronic core-valence (CV) correction, and Davidson (+Q) modification are included in our calculations. The fourteen Ω states generated from the seven Λ-S states are yielded when the spin-orbit coupling (SOC) effect is taken into account by using the Breit-Pauli operator. On the ground of the obtained PECs, the spectroscopic constants of the bound Λ-S and Ω states are evaluated, which reproduce pretty well the available experimental and theoretical values. By virtue of SOC matrix elements between the bound A2Σ+ state and repulsive 4Σ–(I), 2Σ–(I), or 4∏(I) states crossing with the A2Σ+ state PEC, the spin-orbit perturbations in the A2Σ+ rovibrational manifold in the crossing region and the A-state predissociation mechanism are analyzed. It is clearly exhibited that the avoided crossing phenomena between electronic states possessing the same Ω quantum number provide obvious spectroscopic effects in the transition dipole moments (TMDs) and Franck-Condon factors (FCFs) of the A2Σ+-X2Π transition. The radiative lifetimes of the A2Σ+ vibrational sublevels are determined. In addition, we finalized our study of the SeH molecule by optimizing its equilibrium ground state geometry in terms of a restricted coupled cluster approach including singles and doubles with perturbative triples account (RCCSD(T) method) plus CV, SR, and SOC corrections with extrapolating to complete basis set (CBS) limit.

Adsorption of noble fission gas atoms Xe and Kr on Ti- and V-based bare MXenes: An ab-initio DFT investigation

We have studied the adsorption of noble fission gas atoms Xe and Kr on early 3d metal carbide and nitride MXenes, i.e., M2X (M=Ti, V; X= C, N) by performing van der Waals corrected density functional based simulations. These results show that the adsorption of Xe and Kr is stable on all the MXene surfaces considered in this work. For Ti2C, the binding energies and adsorption distances of Xe and Kr are comparable to other 2D materials such as graphene. The replacement of C with N in Ti-based MXene (Ti2N) results in a marginal improvement in the binding strength. In contrast, a noticeable increase in the binding energy is observed for V2X, accompanied by reduction in adsorption distance. It is further demonstrated that the marked increase in Xe/Kr binding energy on V2X as compared to Ti2X is a consequence of much stronger interfacial interaction for the former, highlighted by much larger charge density overlap within the interface region. Moreover, V2X surface increases the selective adsorption of Xe over Kr as indicated by enhanced binding energy difference between Xe and Kr. Further, the adsorption of Xe on oxygen terminated V2C (V2CO2) is also studied which showed that the binding strength reduces by ∼ 0.06 eV due to full oxygen termination. Overall, these results underscore V2X as an efficient Adsorptive material of noble fission gas atoms in comparison to previously studied 2D materials.

Ab-initio investigation of structural, opto-electronic, and thermodynamic properties of ZnAl2Se4 for photovoltaic applications

In this manuscript, the structural, opto-electronic, and thermodynamic properties of ZnAl2Se4 chalcogenide compounds were studied in detail using the full potential linearized augmented plane wave method. The exchange and correlation potentials used in density functional theory were calculated using local density approximation, the generalized gradient approximation (GGA) method, and the modified Becke–Johnson (mBJ) potential using Wien2k code. The obtained results were compared with each other as well as with available experimental data. At ambient conditions, ZnAl2Se4 is a direct wide bandgap (Г–Г) semiconductor with a bandgap of 2.1 and 3.3 eV with GGA and mBJ potentials, respectively. Density of states (DOS; total DOS and Partial Density Of States (PDOS)) and electron density contour plots were in similar accordance with bandgap, showing semiconductive behavior and covalent bonding nature. The optical properties like the real and imaginary parts of the dielectric constant, the energy loss function L( ω), and the conductivity σ( ω) were calculated. Optical aspects show interaction among phonon and electron in terms of long-range and short-range forces. The studied compound is very useful for various linear–nonlinear optical devices, so this compound is very valuable for several linear–nonlinear optical devices. So this manuscript represents a comprehensive approach for calculating the complete set of useful properties of the ZnAl2Se4 compound, which can provide support for understanding various device phenomena such as electrochemical sensing, photovoltaics, and nonvolatile electronic memories.

Exploring the tunability of lead free Ba0.5Sn0.5TiO3 to mimic PbTiO3

Can a material be designed and engineered to use as a replacement for an environmentally unfriendly material? In the specific context of lead titanates, the quest for finding such material replacements is ongoing, beginning from lead free alternatives with simple perovskite compositions, extending to hybrid and double perovskite compositions. In this work, we have demonstrated through ab initio density functional theory investigations the tunability of multiple properties of a simple perovskite Ba0.5Sn0.5TiO3 to mimic that of PbTiO3. Our results show that A-site Sn enhances the polarization of Ba0.5Sn0.5TiO3 closer to that of PbTiO3 and tunes its pressure dependent polarization behavior to become similar to that of PbTiO3 and dissimilar to that of BaTiO3 by reorienting the displacements profiles of A, B site and O atoms to become like that of their counterparts in PbTiO3. Compressive pressures facilitate transition from indirect to direct bandgap, increase the mobility of charge carriers and lead to stronger exciton binding in Ba0.5Sn0.5TiO3 opening up its use for optoelectronics. Ba0.5Sn0.5TiO3 has an early onset of absorption and its absorption spectra in UV range is qualitatively similar to PbTiO3 albeit with reduced absorption peak heights and broadening. The absorption spectra of Ba0.5Sn0.5TiO3 can be modified via application of strains and peak absorption heights can be changed to become similar to that of PbTiO3. We also demonstrate that the dielectric constant as well as refractive index of Ba0.5Sn0.5TiO3 can be modulated to increase (decrease) by applying compressive (tensile) strains. The study of mechanical properties demonstrates that Ba0.5Sn0.5TiO3 is more ductile and is mechanically stable even under higher compressive strains making it excitingly attractive for device applications over other lead-free alternatives that are known to display poor stabilities. These comprehensive investigations demonstrate for the first time that all the physical properties of Ba0.5Sn0.5TiO3 can be tuned as desired for a chosen device application making it a competitive and green replacement to lead titanates.

Ab initio investigation of Co–Ta–Sn Heusler alloys for thermoelectric applications

Heusler alloys have shown to be promising materials for thermoelectric applications. This work presents a theoretical study of Heusler alloys within the GGA-PBE and hybrid (HSE06) approaches. The cubic (C1b) CoTaSn half-heusler compound exhibits semiconductor characteristics and a bandgap of 1.18 eV, when Co occupies the Wyckoff 4c site. On the other hand, the cubic (L21) Co2TaSn full-heusler is a half-metal with a bandgap of 1.36 eV in the spin up channel, when Co in the Wyckoff 4c/8c sites. For both systems, the total magnetic moment agrees with the prediction given by Slater-Pauling rule. The analysis from the Bader charge and ELF functions indicates a formation of covalent-polar bonds in the studied alloys. Also, effective masses were obtained, highlighting this as an important feature for high performance thermoelectrics. From Wannier functions, the thermoelectric parameters were calculated for the CoTaSn alloy and the results compared with the experimental data available in literature.

Ab initio investigation on the ordering mechanism of L12 phase in Al–Zr–Y(Sc) alloy

The L12-Al3Y(Sc) phase promotes the precipitation kinetics of Al3Zr. However, although Al3Y and Al3Sc are both with L12 structures, the mechanisms are not entirely the same due to different structures of the compound composites: Al3(Zr, Sc) has a core-shell structure, while Al3(Zr, Y) does not. Formation mechanisms of core-shell and non-core-shell structures were revealed in this work through analyzing surface energy, interface binding energy, and interface energy. The results showed that the interface energy and the lattice mismatch of Al/Al3Sc and Al/Al3Y are 0.011 J/m2,1.9% and 0.512 J/m2 and 5% respectively. During the growth of Al3(Zr, Sc) with Al3Sc as the heterogeneous core, the interface energy decreased linearly with increasing Zr contents at the interface and eventually a Zr rich shell formed. However, during the formation of Al3(Zr, Y), the interface energy fluctuated with changes in the composition and Zr(Y) content at the interface, eventually forming a composite phase shell of Al3Y(Zr). The diffusion migration energy for Zr atoms in pure Al was 1.102 eV, and it increased by at least 2% near the Al/Al3Sc interface, while it decreased by up to 46.3% near the Al/Al3Y interface. The impact of the L12-Al3Y(Sc) heterogeneous core on the diffusion ability of Zr atoms is crucial for its influence on the kinetics of Al3Zr precipitation.

Concerted versus stepwise proton transfer reactions in the [2, 2'-bipyridyl]-3-3'-diol molecule: A static and dynamic ab-initio investigation.

The double proton transfer (PT) reaction has been investigated in the [2,2'-bipyridyl]-3-3'-diol, a complex molecule where the proton movements is coupled to significant rearrangement of the electronic structure. Moreover, the reaction could be concerted, that is the two protons are exchanged simultaneously, or stepwise, where the two protons are transferred sequentially. To this end, a static exploration of the potential energy surface (PES) was carried together with the analysis of the free-energy surface (FES), both surfaces being evaluated at density functional theory level and different exchange-correlation functionals. While the concerted mechanism has been clearly discharged, the characteristics of the stepwise PT significantly depends on the chosen functionals, some suggesting a clear stepwise mechanism characterized by a stable reaction intermediates and two transitions states, whereas other approaches propend for a asynchronous PT, with a single TS. These features appear on both PES and FES, albeit some differences appears due to their different nature.

On the hydrogen storage performance of metal-decorated beryllium polynitrides: Ab-initio investigations

Recently, two-dimensional materials (2D) have received a lot of attention as potential H2-storage applications. In this way, the recent successful synthesis of beryllium polynitride monolayer has raised our interest regarding the capacity of this promising 2D material to store hydrogen. For this purpose, first principle calculations with DFT-D3 dispersion corrections are used in this work to particularly investigate its hydrogen storage properties. Our results demonstrate that the adsorption energy of a H2 molecule on pristine BeN4 does not exist in the desirable energy range. For this reason, two strategies which are the decoration of lithium metal-atoms and the substitution of beryllium atom by one boron atom are simultaneously performed. The obtained results unveil a marked enhancement of hydrogen adsorption properties where the 2Li-decorated 1B–BeN4 could have 13H2 molecules stored, between values of adsorption energy going from −150 to −600 meV/H2, and a theoretical gravimetric density up to 6.06 wt%, exceeding the US Department of Energy's (DOE) required standards. Using the Van't Hoff equation as a base, the desorption temperature was higher than the critical point of hydrogen.

Crystal chemistry and ab initio investigations of new hard tetragonal C9 and C12 allotropes with edge- and corner-sharing C4 tetrahedra and diamond-related properties

Stable tetragonal C9 and C12 with original topologies have been devised based on crystal chemistry rationale and unconstrained geometry optimization calculations within the density functional theory (DFT). The two new carbon allotropes characterized by corner- and edge-sharing tetrahedra, are mechanically (elastic constants) and dynamically (phonons) stable and exhibit thermal and mechanical properties close to diamond. The electronic band structures show insulating behavior with band gaps close to 5 eV, like diamond.

Influence of vacancy and adsorption of transition metal on performance of single layer of boron pnictides as a supercapacitor electrode: An ab initio investigation

Our work employs density functional theory (DFT), exploring the potential of transition metal adsorption (3d, 4d, and 5d) on boron nitride (BN), boron phosphide (BP), boron arsenide (BAs), and boron antimonide (BSb) as a means of increasing energy storage capacity for supercapacitor electrodes. We observe band gaps of 4.56 eV, 0.97 eV, 0.80 eV, and 0.51 eV for BN, BP, BAs, and BSb, respectively. The pristine BX (X = N, P, As, Sb) monolayers have a maximum quantum capacitance (CQ-max) of 17.15 μF/cm2, 33.52 μF/cm2, 36.91 μF/cm2, and 52.53 μF/cm2. With the adsorption of transition metals, the band gaps decrease due to the additional occupied states, leading to an increase in density near the Fermi region and a higher CQ-max of 146.54 μF/cm2, 132.95 μF/cm2, 121.43 μF/cm2, and 111.76 μF/cm2 for BN, BP, BAs, and BSb when adsorbed on the center of the hexagonal. Upon adsorption of transition metals on the Boron atom, the CQ-max values increase to 137.51 μF/cm2, 210.17 μF/cm2, 190.36 μF/cm2, and 169.79 μF/cm2 for BN, BP, BAs, and BSb, respectively. We also examine mono-vacancies of boron and X atoms (X = N, P, As, Sb) to further explore the potential of these materials for energy storage applications.

Ti, V, Cr, Mn, Co, and Ni substitution effect on structural, electronic, thermodynamic and magnetic properties of MgS and MgSe for spintronics

For the purposes of fitting the characteristics of the Magnesium sulfide (MgS) and, Magnesium selenide (MgSe) semiconductors in Spintronic applications, a theoretical ab-initio investigation of Transition metals (TM=Ti, V, Cr, Mn, Co, Ni) substitution is performed. The equilibrium properties have been studied in the zinc-blende phase of MgS and MgSe. The effects of temperature and pressure on the structural, electronic, thermodynamic, and magnetic properties of our systems are explored as well. It is found that the introduction of the TMs in MgS and MgSe brings out a half-metallic ferromagnetic behavior with 100% polarization around Fermi level in Ti, V, Cr, Co and Ni cases, contrary to the Mn case where the half-metallic feature does not appear. The double exchange mechanism was the mechanism responsible for magnetism in these systems. Finally, the high Curie Temperate (Tc) of the ferromagnetic systems reveals that Ti, Cr and V substitutions could play a significant role in spintronic applications.

Ab Initio Investigation of the Auger Spectra of Methane, Ethane, Ethylene, and Acetylene.

We present an ab initio computational study of the Auger spectra of methane, ethane, ethylene, and acetylene. Auger spectroscopy is an established technique to probe the electronic structure of molecules and exploits the Auger-Meitner effect that core-ionized states undergo. We compute partial decay widths using coupled-cluster theory with single and double substitutions (CCSD) and equation-of-motion CCSD theory combined with complex-scaled basis functions and Feshbach-Fano projection. We generate Auger spectra from these partial widths and draw conclusions about the strength of particular decay channels and trends among the four molecules. A connection to experimental results about fragmentation pathways of the electronic states produced by Auger decay is also made.

Comprehensive AbInitio Investigation of the Phase Diagram of Quasi-One-Dimensional Molecular Solids.

An abinitio investigation of the family of molecular compounds TM_{2}X is conducted, where TM is either TMTSF or TMTTF and X takes centrosymmetric monovalent anions. By deriving the extended Hubbard-type Hamiltonians from first-principles band calculations and evaluating not only the intermolecular transfer integrals but also the Coulomb parameters, we discuss their material dependence in the unified phase diagram. Furthermore, we apply the many-variable variational MonteCarlo method to accurately determine the symmetry-breaking phase transitions, and show the development of the charge and spin orderings. We show that the material-dependent parameter can be taken as the correlation effect, represented by the value of the screened on-site Coulomb interaction U relative to the intrachain transfer integrals, for the comprehensive understanding of the spin and charge ordering in this system.

Ab initio investigations of crystal transition for graphite intercalation compounds during aluminum electrolysiss

This paper studies the crystal transition of graphite intercalation compounds during aluminum electrolysis. Transmission electron microscopy (TEM) analysis demonstrates that the transition induces the structural degradation of carbon cathodes. Buckling of basal planes in the hexagonal compounds contributes to the crystal transition of intercalation compounds from hexagonal to rhombohedral modification. First-principle techniques are used to calculate the structural and electronic properties of graphite intercalation compounds by density-functional theory using the plane wave Pseudo-potential method. The results have demonstrated a close relationship between lattice mismatch and intercalation compounds. The electronic band structure close to the Fermi level has been investigated. The main effect of intercalation compounds is to transfer charge from alkali metal s electron to the carbon pz orbitals, rendering the system metallic. With a decrease of band gap, the crystal transition induces an increase in the interlayer spacing and C–C bond lengths and deteriorates the structural stability of carbon cathodes. The overwhelming majority of contribution to the bands neighboring the Fermi level is from C pz orbital in both intercalation compounds. These findings provide new insights into the mechanisms of carbon cathodes deformation, damage and fracture behavior.

Laser‐induced Fano interference subsumed by electron–phonon coupling in orthorhombic KNbO3nano‐bricks: An ab initio vibrational and Raman spectroscopic investigation

AbstractHydrothermally prepared potassium niobate (KNbO3) nanoparticles are characterized meticulously to explore various crystallographic, microstructural, morphological, optical, compositional, and lattice‐vibrational properties. Laser power‐dependent Raman spectroscopy is employed to study the Fano effect in asymmetrically broadened optic (LO/TO) phonon modes in the orthorhombic KNbO3system, considering interference with the interband electronic continuum. The phonon softening, alterations in charge‐phonon coupling constant, linewidth and lifetime of phonon modes, and so on are explained in the light of theories formulated by Fano, Allen, and Hui, accompanying factor group analysis of the Raman‐active modes. Under local heating via focused laser irradiation, highly sensitive Raman spectra introspect perturbations in the generic vibrations at the first Brillouin zone center and moderations in the constructive/destructive interference conditions of resonant Fano scattering. Density functional theory (DFT)‐based calculations on phonon dispersion, density of phonon states, and relevant thermodynamic attributes decipher the theoretical background. Amid photoexcited electron plasma, the charge‐phonon coupling for distinct modes is strengthened considerably against strong excitation intensity without any unwanted anharmonicity, extensive lattice thermal expansion, phonon decay, or microscopic phase transformation. Finally, the direction of asymmetry, particle–particle, and particle–quasiparticle interactions are illustrated using Feynman diagrams for the associated and phonon modes.