DFT Scheme Research Articles

Promising two dimensional XSe2/SnS (X= Pt, Zr, Hf) vdW heterostructures for overall water splitting with higher carrier mobilities

The transition metal dichalcogenides (TMDs) are considered as promising candidates for their striking performance in optoelectronic properties. We have designed the novel heterostructures XSe2/SnS using XSe2 (X = Pt, Zr, Hf) TMDs. The stabilities of structural, mechanical, dynamical, and thermal are calculated by formation energies, elastic constants, phonon dispersions and AIMD simulations respectively. The hybrid functional (HSE06) is used to calculate the electronic band structures and optical absorption. The DFT scheme (BGC based) indicates that XSe2/SnS vdWHs are viable photocatalyst for overall water splitting over a broad spectrum of light. The absorption spectra exhibit that these photocatalysts have absorption started from visible to the UV region of light in the order of 105. XSe2/SnS heterostructures display high carrier mobilities of order 104. The Gibbs free energies exhibit that PtSe2/SnS heterostructure has spontaneous, whereas other heterostructures need some external energies for overall water splitting. Finally, the corrected STH efficiency of PtSe2/SnS, ZrSe2/SnS and HfSe2/SnS vdW heterostructures are 12.54%, 28.15%, 21.03% respectively. This study depicts that XSe2/SnS (X = Pt, Zr, Hf) heterostructures are feasible candidates for overall water splitting over a broad range of light spectrum.

Theoretical prediction of the mechanical, electronic, optical and thermodynamic properties of antiperovskites A3BO (A = K, Rb and B = Au, Br) using DFT scheme: new candidate for optoelectronic devices application

Theoretical prediction of the mechanical, electronic, optical and thermodynamic properties of antiperovskites A3BO (A = K, Rb and B = Au, Br) using DFT scheme: new candidate for optoelectronic devices application

Two-dimensional CrSe2/GaN heterostructures for visible-light photocatalysis with high utilization of solar energy

Nowadays, designing a two-dimensional (2D) van der Waals heterostructure (vdWH) is one of the most promising methods for improving photocatalytic performance and harvesting solar energy. Here, we proposed a novel CrSe2/GaN vdWH as an efficient photocatalyst for overall water splitting. The elastic constants, phonon dispersion, and ab-initio molecular dynamics simulation show high mechanical and thermodynamic stability. The HSE06 functional reveals that CrSe2/GaN vdWHs possess a direct bandgap. The DFT scheme suggests that the current vdWH belongs to the type-II band alignment and has enough kinetic redox potentials for overall photocatalytic water splitting. The intrinsic electric-field accelerates the photogenerated carrier separation. The carrier mobility of the CrSe2/GaN vdWH is observed to be enhanced as compared to the mobility of the CrSe2 monolayer. Additionally, the optical absorption of the vdWH is found to be high in the visible and ultraviolet regions. The CrSe2/GaN vdWH has a high efficiency of solar-to-hydrogen energy conversion (33.41%). The Gibbs free energy shows that the redox reactions (HER & OER) could be sustained under the action of an external electric-field. Finally, the external strain can tune the band edge and optical absorption of the CrSe2/GaN vdWH for desired applications. Therefore, the CrSe2/GaN vdW heterostructure could be an excellent photocatalyst for water splitting with high solar energy conversion.

Accelerating the Discovery of g-C3N4-Supported Single Atom Catalysts for Hydrogen Evolution Reaction: A Combined DFT and Machine Learning Strategy

Accelerating the Discovery of g-C₃N₄-Supported Single Atom Catalysts for Hydrogen Evolution Reaction: A Combined DFT and Machine Learning Strategy

Accurate Calculation of Excited-State Absorption for Small-to-Medium-Sized Conjugated Oligomers: Multiconfigurational Treatment vs Quadratic Response TD-DFT.

Excited-state absorption (ESA) spectra of π-conjugated compounds are frequently calculated by (quadratic response) time-dependent density functional theory, (QR) TD-DFT, often giving a reasonable representation of the experimental results despite the (known) incomplete electronic description. To investigate whether this is inherent to the method, we calculate here the ESA spectra of small-to-medium-sized oligophenylenevinylenes (nPV) and oligothiophenes (nT) using QR TD-DFT as well as CASPT2 based on CASSCF geometries. CASPT2 gives indeed a reliable, theoretically correct description of the ESA features for all compounds; the computational effort can be reduced without significant loss of accuracy using TD-DFT geometries. QR TD-DFT, based on BHandHLYP and CAM-/B3LYP functionals, fails on short nTs but provides a reasonable description for spectral positions of nPVs and long nTs. The failure on short nTs is, however, only partly due to the incomplete configuration description but, in particular, related to an improper MO description, resulting in an asymmetric energy spacing of the occupied vs unoccupied MOs in the DFT scheme. Longer nTs, on the other side, adapt approximately the MO scheme for alternant hydrocarbons just like in nPVs, while contributions by two triplet excitations combined to a singlet (which inhibits an accurate treatment of polyenes with standard TD-DFT) do not play a relevant role in the current case. For such "well-behaved" systems, a reasonable representation of ESA spectra is found at the QR TD-DFT level due to the rather small energy shifts when including higher-order excitations.

Mechanical and opto-electronic properties of α-MoSi2: a DFT scheme with hydrostatic pressure

Mechanical and opto-electronic properties of α-MoSi2: a DFT scheme with hydrostatic pressure

STABLE STRUCTURES, MAGNETIC AND ELECTRONIC PROPERTIES OF SMALL BIMETALLIC PtCo NANOALLOYS UP 5 ATOMS: A DFT STUDY

In bulk regime size, Co presents an HCP phase and Pt has an FCC phase, both present interesting properties of technological relevance. Co is ferromagnetic and Pt is a good catalyst. Nanoalloying allows us to play with the size and the chemical composition to achieve new properties and functionalities that do not exist at the bulk regime. In this work, we studied the interaction between PtCo atoms and how to affect the chemical order, the magnetic properties and electronic properties of these binary nanoalloys up 5 atoms. Our results show that Co atoms prefer to be localized at sites with the highest coordination in nanoalloys with 5 atoms, in PtCo clusters with 4 atoms, we found planar geometries as the stable ones. All the nanoalloys have a favorable atom mixing; the bimetallic clusters considered in this study show magnetic behavior and present a ferromagnetic-like order where the value of the total magnetization depends on the number of Co atoms of the cluster. We have considered the vertical ionization potential to determine the donation of electrons and the capture of electrons is studied through the electronic affinity and these are related to the chemical hardness which is an index of catalytic activity. This study was done into the DFT scheme as implemented in the SIESTA code using a generalized gradient approximation.

Improving Bit Error Rate of MIMO-OFDM System Using Discrete Wavelet Transformation

This paper has developed a discrete wavelet transform (DWT) for multicarrier modulation in MIMO-OFDM system. The proposed system used additive Gaussian white noise (AGWN) and Rayleigh flat fading channel with respect to SNR using binary phase shift keying (BPSK). The algorithms for various scenarios of MIMO-OFDM system have been developed and simulated in MATLAB environment. The performance metric of the system was based on bit error ratio (BER) variation over values of signal to noise ratio (SNR) for different transmit and receive antennas including single input multiple output (SIMO) arrangement. The simulation results showed that the performance of DWT based MIMO-OFDM outperformed DFT based MIMO-OFDM. For the 2×1, 2×2, 2×3 MISO and MIMO systems, the DWT scheme offered reduced BER of 1.803e-05, 1.502e-05, and 1.413e-05 against 0.005847, 0.005361, and 0.005325 for the DFT scheme with respect to signal to noise ratio (SNR) at 10 dB. Generally, the results showed that using DWT scheme in OFDM for wireless communication system does not require an extra subcarrier to provide cyclic prefix function that serves as additional cost burden and reduces bandwidth.

A Simple Effective SCF Method for Computing Optical Gaps in Organic Chromophores

Photoluminescence effects in organic chromophores are of significant importance and requires precise description of low lying excited states. In this communication, we put forward an alternative time-independent DFT scheme for computing lowest single-particle excitation energy, especially for singlet excited state. This adopts a recently developed "virial"-theorem based model of singlet-triplet splitting which requires a DFT calculation on closed shell ground state and a restricted open-shell triplet excited state, followed by a simple integral evaluation. This produces vertical excitation energies in small molecules, linear and non-linear polycyclic aromatic hydrocarbon and organic dyes in comparable accuracy to the TDDFT. We also explore the functional dependency of present method with three different functionals (B3LYP, wB97X and CAM-B3LYP) for polyenes and linear acenes. A systematic comparison with literature value illustrates the validity and usefulness of the present scheme in determining optical gap with fair computational cost.

H/D Isotope Effects in Keto-Enol Tautomerism of β-Dicarbonyl Compounds —Importance of Nuclear Quantum Effects of Hydrogen Nuclei—

Abstract Deuterium isotope effects in the keto-enol tautomerism of β-dicarbonyl compounds (malonaldehyde, acetylacetone, dibenzoylmethane, and avobenzone) have been studied using a B3LYP+D functional level of multi-component density functional theory (MC_DFT), which can directly take nuclear quantum effects (NQEs) of the hydrogen nuclei into account. We clearly show that the keto-enol energy difference becomes smaller by deuterium substitution, which is in reasonable agreement with the corresponding experimental evidence. Our MC_DFT study also reveals the hydrogen/deuterium (H/D) isotope effect in geometries and shows that the deuterium substitution weakens the intramolecular hydrogen-bonded interaction in the enol form. Direct treatment of NQEs of hydrogen nuclei via the MC_DFT method is essential for analyzing the H/D isotope effect in keto-enol tautomerism of β-dicarbonyl compounds. Such isotope effects cannot be reproduced in the conventional DFT scheme with harmonic zero-point vibrational corrections.

Physical properties of MAX phase Zr2PbC under pressure: Investigation via DFT scheme

This study investigates the physical properties of Zr2PbC under pressure using DFT. The lattice constants drop linearly from a = 3.41 to 2.97 Å and c = 14.96 to 13.60 Å with increasing pressure ranging from 0 to 100 GPA. The negative formation enthalpy confirms the thermodynamic stability the pressurized phases. Moreover, the Born stability factors are satisfied by elastic constants, ensuring the mechanical stability of pressurized and non-pressurized Zr2PbC. The compound switches from brittle to ductile and the maximum ductility is observed at 20 GPa pressure, as the Pugh's ratio decreases from 0.67 to 0.37 and Poisson's ratio increases from 0.23 to 0.34. The anisotropy becomes more intensive with pressure. Although the band structure has been tuned under pressure, the metallic nature is retained. The co-existence of covalent, metallic, and ionic bonding is observed in Zr2PbC. The optical functions suggest the potential applications of this compound in various sectors.

Novel synthesis, spectral characterisation and DFT calculation of (3,4-bis((E)-(substituted-dichlorobenzylidene)amino) phenyl) (phenyl) methanone derivatives

The organic compounds containing (3,4-bis(( E )-(2,3-dichlorobenzylidene)amino)phenyl) (phenyl) methanone (1) , (3,4-bis(( E )-(2,6-dichlorobenzylidene)amino)phenyl)(phenyl) methanone (2) and (3,4-bis(( E )-(3,4 dichlorobenzylidene)amino) phenyl)(phenyl) methanone (3) were synthesised in the current study. The synthesized methanone derivatives 1 – 3 are characterized by elemental analysis, mass spectral studies, FT-IR, 1 H& 13 C NMR. Due to the basis set to derive the optimised geometry, dipole moment, HOMO-LUMO energy, molecular electrostatic potential, Mulliken charge population, and first-order molecular hyperpolarization (β), theoretical calculations were carried out using the DFT (B3LYP) strategy with 6-31G(d, p).

Solvent-free synthesis, spectral, crystal study and DFT calculations of (E)-1-benzyl-N-(4-fluorobenzylidene)piperidin-4-amine and (E)-1-benzyl-N-(naphthalen-2-ylmethylene)piperidin-4-amine

• Synthesis of ( E )-1-benzyl-N-(4-fluorobenzylidene)piperidin-4-amine ( I ) and ( E )-1-benzyl-N-(naphthalen-2-ylmethylene)piperidin-4-amine ( II ) by solvent-free greener method. • FT-IR, NMR and Single crystal X-ray diffraction studies confirmed the formation of compound I and II . • Crystal structure of compound I and II having orthorhombic and monoclinic, and its geometric parameters were compared with the theoretical values. Two Schifff's bases ( E )-1-benzyl-N-(4-fluorobenzylidene)piperidin-4-amine ( I) and ( E )-1-benzyl-N-(naphthalen-2-ylmethylene)piperidin-4-amine ( II) were prepared by ZnFe 2 O 4 catalyst assisted microwave irradiated condensation method under solvent-free conditions. Synthesised Schiff's bases ( I ) and ( II ) were crystallized by a slow evaporation technique. High-quality single crystals of ( I) and ( II ) were developed from ethanol and therefore reasonable crystal measurements are 0.28 × 0.26 × 0.21 (I) and 0.21 × 0.25 × 0.35 mm (II) and these crystals possess orthorhombic and monoclinic crystal system with the space group of P2 1 and P2 1 /c respectively. Theoretical calculations were performed utilizing DFT (B3LYP) strategy with 6-31G(d,p) because of the basis set to derive the optimized geometry, dipole moment, HOMO-LUMO energy, molecular electrostatic potential, Mulliken charge population and first-order molecular hyperpolarizality (β). Further, these Schiff's bases were characterized by elemental analysis, FT-IR, 1 H & 13 C NMR and HR-MS spectroscopy.

Chemical and Physical Viewpoints About the Bonding in Fullerene–Graphene Hybrid Materials: Interaction on Pristine and Fe-Doped Graphene

A DFT scheme was adopted to study the noncovalent/covalent attachment of fullerenes (C60, Si24C36, and B24N36) to graphene and Fe-doped graphene nanosheets (FeG). Geometrical, energetic, and electr...

Synthesis, structural characterization, DFT studies and biological activity of Cu(II) and Ni(II) complexes of novel hydrazone

Novel hydrazone 2-(2-((1E,2E)-2-(2-phenylhydrazineylidene)propylidene)hydrazineyl)pyridine and its nickel(II) and copper(II) complexes have been synthesized and characterized. The ligand (H2PGl) was prepared by the condensation reaction of 1-(2-phenylhydrazineylidene)propan-2-one and 2-hydrazinopyridine. The crystal structure of Ni(II) complex was determined. In both Ni(II) and Cu(II) complexes, H2PGl act as a neutral tridentate ligand forming two fused five-membered chelation rings through NNN set of donor atoms. Octahedral geometry is proposed for both chelates as illustrated in both magnetic and spectroscopic data. ESR spectroscopy was performed for Cu(II) complex which exhibited a considerable Cu–Cu interaction and harmonize directly with measured magnetic moment. The molecular modeling structures were optimized and showed the bond length, bond angle, reactivity, MEP and atomic charges for all the title frameworks. Hypothetical infrared intensities and 1H NMR of H2PGl was estimated on the basis of DFT scheme. A comparison of the experimental and theoretical data was very useful in creating correct assignments and understanding the basic chemical shift. Biological activity of the synthesized compounds were investigated versus some Gram positive, Gram negative bacteria and some fungal strains. Also, the antitumor activity was investigated.

First principles study of ferromagnetism, optical and thermoelectric behaviours of AVO3 (A = Ca, Sr, Ba) perovskites

The structural, magnetic, optical and thermoelectric characteristics of CaVO3, SrVO3 and BaVO3 perovskite compounds computed by DFT scheme are presented. The electronic properties are computed to confirm the half-metallic ferromagnetism. The comparisons of crystal field, John Teller and the exchange energies elucidate that the electronic spins play a major role in inducing ferromagnetism. The complete set of computed optical parameters illustrate that the investigated perovskites are active for the visible and ultraviolet regions. The thermoelectric characteristics thoroughly elaborated, within the temperature range 200–800K, illustrate that the perovskites are also suitable for the energy renewable device applications.

Magnetism, optical, and thermoelectric response of CdFe2O4 by using DFT scheme

Comparative analysis of electronic, magnetic, optical, and thermoelectric properties of CdFe2O4, calculated by employing PBEsol + mBJ has been done. The PBEsol reveals metallic nature, while TB-mBJ illustrates ferromagnetic semiconducting behavior. The reasons behind the origin of ferromagnetism are explored by observing the exchange, crystal field, and John–Teller energies. The optical nature is investigated by analyzing dielectric constants, refraction, absorption coefficient, reflectivity, and optical conductivity. Finally, thermoelectric properties are elaborated by describing the electrical and thermal conductivities, Seebeck coefficient, and power factor. The strong absorption for the visible energy and high power factor suggest CdFe2O4 as the potential candidate for renewable energy applications.

Reexamination of structures, stabilities, and electronic properties of holmium-doped silicon clusters HoSi n (n = 12-20).

The total energies, growth patterns, equilibrium geometries, relative stabilities, hardnesses, intramolecular charge transfer, and magnetic moments of HoSi n (n = 12-20) clusters have been reexamined theoretically using two different density functional schemes in combination with relativistic small-core Stuttgart effective core potentials (ECP28MWB) for the Ho atoms. The results show that when n = 12-15, the most stable structures are predicted to be exohedral frameworks with a quartet ground state, but when n = 16-20, they are predicted to be endohedral frameworks with a sextuplet ground state. These trend in stability across the clusters (gauged from their dissociation energies) was found to be approximately the same regardless of the DFT scheme used in the calculations, with HoSi13, HoSi16, HoSi18, and HoSi20 calculated to be more stable than the other clusters. The results obtained for cluster hardness indicated that doping the Ho atom into Si13 and Si16 leads to the most stable HoSi n clusters, while doping Ho into the other Si n clusters increases the photochemical sensitivity of the cluster. Analyses of intracluster charge transfer and magnetic moments revealed that charge always shifts from the Ho atom to the Si n cluster during the creation of exohedral HoSi n (n = 12-15) structures. However, the direction of charge transfer is reversed during the creation of endohedral HoSi n (n = 16-20) structures, which implies that Ho acts as an electron acceptor when it is encapsulated in the Si n cage. Furthermore, when the most stable exohedral HoSi n (n = 12-15) structures are generated, the 4f electrons of Ho are virtually unchanged and barely participate in intracluster bonding. However, in the most stable endohedral HoSi n (n = 16-20) frameworks, a 4f electron does participate in bonding. It does this by transferring to the 5d orbital, which hybridizes with the 6s and 6p orbitals and then interacts with Si valence sp orbitals. Meanwhile, the total magnetic moments of the HoSi n (n = 16-20) clusters are considerably higher than those of HoSi n (n = 12-15). Interestingly, the endohedral HoSi16 and HoSi20 clusters can be viewed as the most suitable building blocks for novel high-density magnetic storage nanomaterials and for novel optical and optoelectronic photosensitive nanomaterials, respectively.

Constrained subsystem density functional theory.

Constrained Subsystem Density Functional Theory (CSDFT) allows to compute diabatic states for charge transfer reactions using the machinery of the constrained DFT method, and at the same time is able to embed such diabatic states in a molecular environment via a subsystem DFT scheme. The CSDFT acronym is chosen to reflect the fact that on top of the subsystem DFT approach, a constraining potential is applied to each subsystem. We show that CSDFT can successfully tackle systems as complex as single stranded DNA complete of its backbone, and generate diabatic states as exotic as a hole localized on a phosphate group as well as on the nucleobases. CSDFT will be useful to investigators needing to evaluate the environmental effect on charge transfer couplings for systems in condensed phase environments.

Realistic Energy Surfaces for Real‐World Systems: An IMOMO CCSD(T):DFT Scheme for Rhodium‐Catalyzed Hydroformylation with the 6‐DPPon Ligand

The hydroformylation of terminal alkenes is one of the most important homogeneously catalyzed processes in industry, and the atomistic understanding of this reaction has attracted enormous interest in the past. Herein, the whole catalytic cycle for rhodium-catalyzed hydroformylation with the 6-diphenylphosphinopyridine-(2H)-1-one (6-DPPon) ligand 1 was studied. This catalytic transformation is challenging to describe computationally, since two requirements must be met: 1) changes in the hydrogen-bond network must be modeled accurately and 2) bond-formation/bond-breaking processes in the coordination sphere of the rhodium center must be calculated accurately. Depending on the functionals used (BP86, B3LYP), the results were found to differ strongly. Therefore, the complete cycle was calculated by using highly accurate CCSD(T) computations for a PH3 model ligand. By applying an integrated molecular orbital plus molecular orbital (IMOMO) method consisting of CCSD(T) as high level and DFT as low-level method, excellent agreement between the two functionals was achieved. To further test the reliability of the calculations, the energetic-span model was used to compare experimentally derived and computed activation barriers. The accuracy of the new IMOMO method apparently makes it possible to predict the catalytic potential of real-world systems.