Papers by Keyword: Density Functional Theory (DFT)

Abstract: Suppressing the expansion of Single Shockley-type stacking faults (1SSFs) is critical for the growing demand of high-performance power devices. However, the underlying suppression mechanism has not yet been fully elucidated. Through proton ion implantation studies, we have established a fundamental approach by modeling this phenomenon. Carbon vacancy (V_c) generated by high-energy proton implantation are found to play a significant role in suppressing the expansion of 1SSFs.

Abstract: This study investigates the corrosion inhibition of low carbon steel using a synergistic blend of Citrus sinensis extract and 1H-benzotriazole. The inhibition efficiency was evaluated using Density Functional Theory (DFT) with the B3LYP/6-31G(d) basis set and Monte Carlo simulations. Quantum chemical parameters such as EHOMO, ELUMO, ionization potential (IP), and electron transfer (ΔN) were calculated. The results indicate that the mixed inhibitor provides superior corrosion protection compared to individual inhibitors, with adsorption energies of-20511.53 kcal/mol for the combination, significantly higher than-175.09 kcal/mol for Citrus sinensis and-10359.80 kcal/mol for 1H-benzotriazole alone. The combined inhibitor demonstrated enhanced electron donation, reducing the energy gap (ΔE) and improving the stability of adsorption on the steel surface. This suggests that the synergistic interaction of the inhibitors leads to a more efficient, sustainable corrosion protection method, offering an environmentally friendly alternative for steel protection.

Abstract: In this study, we present positron lifetime calculations for diamond, including the defect-free bulk, vacancies and vacancy clusters, as well as grain boundaries, using Two-Component Density Functional Theory. Our results show a positron bulk lifetime of 103 ps and a mono-vacancy lifetime of145 ps, which is in agreement with experimental data. We calculated positron lifetimes for vacancy clusters from 2 up to 40 missing atoms, resulting in lifetimes between 168 to 365 ps. From these results, we derived a function that correlates the cluster size with the respective positron lifetime.Furthermore, we computed the positron lifetime of 124 ps for a grain boundary, which is between the bulk and mono-vacancy lifetime. Our results will be used to interpret measured positron lifetime spectra in diamond.

Abstract: We investigate the hole formalism and positron screening within the framework of Den sity Functional Theory (DFT). This study revisits the Local Density Approximation (LDA) and its extensions - such as semilocal functionals and the Weighted Density Approximation (WDA), show ing their importance in modeling exchange and correlation potentials. We further examine the two-component density functional approach to describe electron-positron interactions, with particular em phasis on the formation of the electron screening cloud around the positron site. The performance of various computational techniques in describing charge inhomogeneities and positron surface states is critically assessed. Moreover, we identify the limitations of conventional models in low-dimensional systems and propose a novel method based on the electronic dielectric response to improve the accu racy of positron screening predictions.

Abstract: Thermoelectric materials are useful for various application in daily life. Their application such as sensors, generators and electronic components, making thermoelectric materials widely studied. Antiperovskite compounds that can have semiconducting behaviour is probable candidate for thermoelectric materials. In this article, thermoelectric properties of anti-perovskite X₃SiO (X = Sr and Ba) were investigated using density functional theory (DFT) method and Boltzmann Transport Equations (BTE). Electronic properties such as band structure, partial density of states were computed using the generalized gradient approximation with Perdew-Burke-Ernzerhof (GGA-PBE) functional in CASTEP code. The thermoelectric properties such as Seebeck coefficient, electrical conductivity, and power factor are calculated using BoltzTraP code that utilised BTE. The calculated band structures of Ba₃SiO and Sr₃SiO show that these compounds having semiconductor behaviour with direct band gap of 0.44 and 0.43 eV respectively at Γ-Γ k-point. It was found that Ba₃SiO is a better candidate for thermoelectric materials due to its higher Seebeck coefficient (-4.90 10^-4 V/K) at room temperature compared to calculated Seebeck coefficient (-5.84 10^-4 V/K) of Sr₃SiO. The power factor value of Ba₃SiO which is 2.96 x 10^-4 W/mK² is also higher compared to power factor of Sr₃SiO at 7.12 x 10^-7 W/mK² at room temperature.

Abstract: In this work, we present the results of the calculation of the electronic and optical properties of titanium dichalcogenide materials TiX₂ (X=S, Se, Te). These calculations were performed using the QUANTUM-ESPRESSO package, based on the density functional theory and the pseudopotential technique. The results obtained showed that TiS₂ is a semi-metallic compound, this character is due to a very small overlap between the density of states p-orbitals of S and d-orbitals of the Ti atom in the vicinity of the Fermi level. While TiSe₂ and TiTe₂ indicate the metallic characters. At the Fermi level, the total density of states is 0.77 states/eV and 1.13 states/eV for both compounds respectively. On the other hand, the optical properties of these materials such as the real and imaginary parts of dielectric function ε₁ and ε₂, respectively, the refractive index, the absorption, the reflectivity, and the loss function were investigated based on Kramers-Kroning relations in the energy range of 0 to 20 eV. In the infrared region, the reflectivity spectrum R(ω) is close to 100% for TiX₂ (X= S, Se, Te), suggesting their potential application as a good coating material.

Abstract: In the last few years, materials that may have favorable thermoelectric properties have aroused great interest, because they have the ability to generate electricity through the thermoelectric effect. In this work, the temperature effect on the transport properties of a ZnSb compound having an orthorhombic structure is studied, using the local density approximation with the modified approach of Becke and Johnson (LDA + mBJ), within the framework of density functional theory (DFT). To do this, we use the BoltzTrap package implemented in the Wien2k code, with a constant relaxation time of the charge carriers. All transport properties were studied in the temperature range of 300 to 600 K. Moreover, for high temperatures, the prediction of the figure of merit of ZnSb indicates that the compound is much more suitable for thermoelectric devices. Also, the Pauli magnetic susceptibility of zinc antimonide showed that this material is non-magnetic.

Abstract: The flavonoglycone hesperidin is recognized as a potent anti-inflammatory, anticancer, and antioxidant agent. However, its poor bioavailability is a crucial bottleneck regarding its therapeutic activity. Gold nanoparticles are widely used in drug delivery because of its unique properties that differ from bulk metal. Hesperidin loaded gold nanoparticles were successfully prepared to enhance its stability and bioactive potential, as well as to minimize the problems associated with its absorption. The free radical scavenging activities of hesperidin, gold nanoparticles, and hesperidin loaded gold nanoparticles were compared with that of Vitamin C and subsequently evaluated in vitro using 2,2-diphenyl-1-picrylhydrazyl assay. The antioxidant pharmacophore-based structure-activity relationship analysis was assessed by the density functional theory as well as quantum chemical calculations. Moreover, the structural properties were utilized using Becke’s three-parameter hybrid exchange and Lee-Yang-Parr’s correction of functional approaches. Hesperidin-loaded gold nanoparticles were found to decrease hydrogen peroxide (H₂O₂₎ and thus induce Deoxyribonucleic acid (DNA) instability. In addition, hesperidin-gold nanoparticles were observed to display important antioxidant potential as well as ameliorate the functional activity of macrophages against Escherichia coli, possibly protecting DNA. These particles might be appropriate for clinical trials and could prove useful for the treatment of various life-threatening disorders.

Abstract: Structural and spectroscopic properties of Ruhemann’s purple (RP) and its transition metal coordination complexes were calculated using theoretical chemistry techniques. The obtained information described RP and its coordination complexes with the transition metal ions [Cr(II), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)]. The procedures involved calculations of what are called density functional theory (DFT) and time-dependent DFT (TD-DFT). These methods optimized what is called, in the codes of theoretical chemistry, the hybrid density B3LYP function employing the 6‐311++G(d,p) and LANL2DZ basis sets. The RP geometries, bond lengths, angles, quantum chemical parameters, and excitation spectra indicate that the RP is well able to coordinate with a transition element ion. Then the correlation of these theoretical results with experimental observations provides a detailed description of the structural and spectroscopic properties of RP compounds. The inclusion of solvent effects causes a blue shift in all theoretical excitation spectra. In summary, this work leads to an understanding of the characteristics of transition metal complexes with Ruhemann’s purple. These materials can be applied in forensic chemistry as reagents in developing latent fingerprints.

Abstract: Generally, it is difficult to generate a high-performance pure blue emission organic light-emitting diode (OLED). That is because the intrinsically wide band-gap makes it hard to inject charges into the emitting layer in such devices. To solve the problem, carbazole derivatives have been widely used because they have more thermal stability, a good hole transporting property, more electron rich (p-type) material, and higher photoconductivity. In the present work, novel copolymers containing donor-acceptor-acceptor-donor (D-A-A-D) blue compounds used for OLEDs were investigated. The theory of the geometrical and electronic properties of N-ethylcarbazole (ECz) as donor molecule (D) coupled to a series of 6 acceptor molecules (A) for advanced OLEDs were investigated. The acceptors were thiazole (TZ), thiadiazole (TD), thienopyrazine (TPZ), thienothiadiazole (TTD), benzothiadiazole (BTD), and thiadiazolothienopyrazine (TDTP). The ground state structure of the copolymers were studied using Density Functional Theory (DFT) at B3LYP/6-31G(d) level. Molecular orbital analysis study indicated 3 investigated copolymers (ECz-diTZ-ECz, ECz-diTD-ECz, ECz-diBTD-ECz) have efficient bipolar charge transport properties for both electron and hole injection to the TiO₂ conduction band (4.8 eV). In addition, the excited states electronic properties were calculated using Time-Dependent Density Functional Theory (TD-DFT) at the same level. Among these investigated copolymer ECz-diTZ-ECz and ECz-diTD-ECz showed the maximum absorption wavelengths (λ_abs) with blue emitting at 429 and 431 nm, respectively. The results suggested that selected D-A-A-D copolymers can improve the electron- and hole- transporting abilities of the devices. Therefore, the designed copolymers would be a promising material for future development of light-emitting diodes, electrochromic windows, photovoltaic cells, and photorefractive materials.