Orbital Band Research Articles

Ensemble Monte Carlo transport studies of zinc-blende cuprous halides

We present a comprehensive theoretical analysis of intrinsic high-field transport in cuprous halides: CuCl, CuBr, and CuI. Ensemble Monte Carlo transport simulations were performed based on analytical approximations of the multi-valley and three-band electronic structure model. The deformation potentials, extracted from carrier–phonon interaction matrix elements calculated via the Wannier function approach, were employed to determine scattering rates. Our detailed analysis uncovers intriguing transport characteristics based on the complex valence band structures, resulting from spin–orbit coupling and band inversion. Remarkably, the hole mobility in CuI was exceptionally high, reaching up to 193 cm2/V s, while CuCl exhibited unusual temperature dependencies in hole transport. Additionally, the electron mobility in CuI was found to be 254 cm2/V s, indicating a minimal disparity between carrier mobilities, which is advantageous for optoelectronic applications.

Bifunctional catalytic activity of anion-doped LaSrCoO4 for oxygen reduction and evolution reactions.

Here, we synthesized Co-based, anion-incorporated‍ ‌R‌u‌d‌d‌l‌e‌s-d‌e‌n‌-‌Popper perovskite electrocatalysts (LaSrCoO4-x X y ) and compared their catalytic performances in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The ORR mechanism with the newly synthesized F-doped LaSrCoO4 catalyst was dominated by a four-electron process, and the number of electrons involved in the reaction increased compared with that for LaSrCoO4. The OER activity of the hydride-doped LaSrCoO4 catalyst was the highest among the LaSrCoO4 system catalysts. Density functional theory calculations revealed that there is a correlation between the Co 3d unoccupied orbital band centre and the OER activity. The addition of anions and substitution of metal sites improved the ORR and OER activities of the catalysts. Our findings confirmed that the addition of heteroatom anions can improve the activity of perovskite-type electrocatalysts, promoting their application in various fields.

Body Mass Index Is Associated With Orbital Pulley Degeneration Syndrome, Including Sagging Eye Syndrome

Sagging eye syndrome (SES), esotropia with high myopia including heavy eye syndrome, and age-related esotropia (ARE)-collectively termed orbital pulley degeneration syndrome (OPDS)-are characterized by strabismus with orbital pulley lateral rectus-superior rectus band impairment. Herein, we examined body mass index (BMI) in OPDS to determine SES-associated anthropometric characteristics. Retrospective cohort study. We compiled and analyzed the BMI of patients aged ≥50 years who underwent strabismus surgery at a single center in Shizuoka, Japan, between July 2020 and March 2023. BMI (kg/m2) was categorized into 4 groups: <18.5, 18.5 to 21.9, 22 to 24.9, and ≥25. As the boundary between OPDS and SES is ambiguous, we assumed a pure SES group by excluding patients with ARE and esotropia with high myopia from the OPDS group. Overall, 204 patients (age: 67.7 ± 9.7 years) were included in the study. There were 78/126 and 49/119 patients in the OPDS/non-OPDS and SES/non-SES groups (age: 70.4 ± 9.5/66.0 ± 9.6 years, P = .002 and 75.0 ± 6.0/66.6 ± 9.5 years, P < .001; BMI: 21.2 ± 3.3/23.2 ± 3.0 kg/m2, P < .001 and 21.2 ± 3.3/23.1 ± 3.0 kg/m2, P = .003), respectively. In the BMI-stratified analysis, OPDS and SES were more prevalent in the <18.5 BMI group than in the 22 to 24.9 and ≥25 BMI groups (P < .001 and P = .006, respectively). Logistic regression analysis, adjusted for age and sex, showed that lower BMI was associated with a higher prevalence of OPDS and SES. Patients with OPDS, including SES, had lower BMI than other patients with strabismus. Therefore, BMI may be a clinical clue to SES.

First-principle study of the ground-state crystal structure and optoelectronic response of CsPbX3 (X= Cl, Br, I) for photovoltaic applications

The optoelectronic response and ground state crystal structure of tetragonal (P4/mbm), orthorhombic (Pmnb) and monoclinic (P21/m) phases of CsPbX3 (X = Cl, Br, I) are studied for optoelectronic applications using first principle simulations. Electric field gradient (EFG) and magnetic hyperfine interactions are investigated to explore the charge distributions surrounding the nucleus and local magnetic environment of the atomic nucleus. The orthorhombic phase of these compounds is more stable having lowest ground-state energy compared to tetragonal and monoclinic phases. The understudied halide perovskites have direct band gap nature and spin orbit coupling (SOC) effect splits Pb-p and X-p orbitals at the edges of conduction and valence band (CB and VB) respectively. At the edge of VB, the strongly hybridized X-p and Pb-p orbital and direct band gap nature of CsPbX3 is excellent for the light absorption and photovoltaic (PV) applications. The n-i-p configuration (FTO/ETL/CsPbX3/HTL/Au) of the simulated structure shows that CsPbI3 has improved power conversion efficiency (PCE) of 22.48 % and 22.32 % and quantum efficiency (QE) about ∼80 % in tetragonal and monoclinic phases respectively. The Pb and Cs values of EFG tensor in z-direction (Vzz) are close to each other, which show that the distribution of electronic charge density is similar near these nuclei. Moreover, Cs-s orbital has negligible contribution and Pb-p and I-p orbitals have higher contribution in the hyperfine field (HFF). The negative HFF indicates the opposite HFF contribution.

Electronic structure and resonant inelastic x-ray scattering in Ca3Ru2O7

We have investigated the electronic structure of the transition metal oxide Ca3Ru2O7 within density-functional theory using the generalized gradient approximation while considering strong Coulomb correlations in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band structure method. Ca3Ru2O7 can be classified as a Mott insulator since it was expected to be metallic from band structure calculations. We found that the magnetic ground state of Ca3Ru2O7 possesses an AFM−b magnetic structure with the Ru spin moments ordered antiferromagnetically along the b axis. We have investigated the resonant inelastic x-ray scattering (RIXS) spectra at the Ru and Ca K, L3, and M3 edges as well as at the OK edge. The experimentally measured RIXS spectrum of Ca3Ru2O7 at the Ru L3 edge possesses a sharp feature ≤2eV corresponding to transitions within the Ru t2g levels. The excitation located from 2 to 4 eV is due to t2g→ eg transitions. The third wide structure situated at 4.5−11eV appears due to transitions between the Ru 4dO states derived from the tails of oxygen 2p states and eg and t2g states. The RIXS spectra at the Ru L3 and M3 edges are quite similar. However, the corresponding RIXS spectra at the Ca site are quite different from each other due to the significant difference in the widths of core levels. The RIXS spectrum at the OK edge consists of three major inelastic excitations. We found that the first two low energy features ≤2.5eV are due to interband transitions between occupied and empty Ot2g states which appear due to the strong hybridization between oxygen 2p and Ru t2g states in close vicinity to the Fermi level. The next major peak between 2.5 and 8 eV reflects interband transitions from occupied O2p to empty Ot2g states. A wide energy interval between 4 and 11 eV is occupied by rather weak O2p→Oeg transitions. Published by the American Physical Society 2024

Adsorption of SF6 decomposition gases (SO2 and SOF2) onto pristine and transition metal modified WSe2 monolayers: A systematic DFT study

The properties of SF6 characteristic decomposition products (SO2 and SOF2) adsorbed on intrinsic and transition metal atom modified WSe2 monolayers were studied based on the first principles. The adsorption structure, adsorption energy, electron transfer, density of states, electron differential density, work function, and desorption properties are comprehensively discussed. In addition, the charge transfer in the adsorption system was qualitatively analyzed by using the frontier molecular orbital theory and energy band. The results show that the pristine WSe2 monolayer has poor sensing performance for SO2 and SOF2. Effective modification methods can significantly increase the adsorption activity of the monolayer surface. The modification methods of transition metal atom adsorption and doping are discussed respectively. The modified monolayer all exhibit good sensing properties compared to the pristine monolayer due to the significant electronic hybridization between the impurity atoms and the gas molecules. Finally, the recovery response time of gas molecules from transition metal atom modified WSe2 monolayer is evaluated to evaluate its potential application in the detection and removal of fault gases in SF6 insulation equipment. Our work is not only important for predicting novel transition metal sulfide sensing materials, but also provides theoretical guidance for further developing WSe2-based sensors and scavengers for environmental monitoring applications.

Exciton Localization Modulated by Ultradeep Moiré Potential in Twisted Bilayer γ-Graphdiyne.

Twisted moiré superlattice is featured with its moiré potential energy, the depth of which renders an effective approach to strengthening the exciton-exciton interaction and exciton localization toward high-performance quantum photonic devices. However, it remains as a long-standing challenge to further push the limit of moiré potential depth. Herein, owing to the pz orbital induced band edge states enabled by the unique sp-C in bilayer γ-graphdiyne (GDY), an ultradeep moiré potential of ∼289 meV is yielded. After being twisted into the hole-to-hole layer stacking configuration, the interlayer coupling is substantially intensified to augment the lattice potential of bilayer GDY up to 475%. The presence of lateral constrained moiré potential shifts the spatial distribution of electrons and holes in excitons from the regular alternating mode to their respective separated and localized mode. According to the well-established wave function distribution of electrons contained in excitons, the AA-stacked site is identified to serve for exciton localization. This work extends the materials systems available for moiré superlattice design further to serial carbon allotropes featured with benzene ring-alkyne chain coupling, unlocking tremendous potential for twistronic-based quantum device applications.

Ab-initio investigation of the structural, electronic and optical properties of CsPbBr3 perovskite under pressure using the DFT-1/2 method

Pressure-induced phase transitions in metal halide perovskites lead to significantly different material properties and offer great potential for diverse applications. The electronic, structural, and optical properties of Cesium lead bromide (CsPbBr3) crystals are investigated using density functional theory (DFT) to draw an integrated picture of orbital morphology, absorption spectra, and band gap values. Spin-orbit coupling and DFT-1/2 correction are used to gain a better insight into electronic properties and band splitting in the cubic phase. Calculations of pressure-induced phase transitions, electronic band gap engineering, and manipulation of optical absorption edges of CsPbBr3 are conducted. In the cubic and tetragonal crystal lattices, a band gap closure and opening occurs demonstrating a Dirac cone upon application and increase of pressure. Indeed, in the tetragonal lattice of CsPbBr3, a topological band occurs. Orthorhombic perovskite crystal lattice undergoes successive direct-indirect and indirect-direct band gap transitions, followed by a space group change at extreme pressures. However, under pressure, orthorhombic non-perovskite lattice experiences a sudden band gap breakdown. Phase and band gap transitions are explained by orbital hybridizations and structural symmetry evolution (e.g., bond length contraction/dilation and octahedral cage rotation/distortion). These results provide comprehensive guidelines for further experimental studies on pressure engineering, advanced photovoltaic and optoelectronic applications, discovering and understanding new topological band structures of perovskite materials.

Weak oxidant fraction in the microwave plasma influencing the evolution of nanocrystalline-diamond–imbedded diamond–like carbon network at low temperatures and its orbital hybridization dependent wide optical band gaps

The diamond-like carbon (DLC) thin films having intrinsic nanocrystalline diamond (NCD) components were synthesized on bare glass substrates at 300 °C, employing a (C2H2/CO2/H2/) gas mixture in MW-PECVD. Relevant influence of the weak oxidant fraction [F = CO2/(CO2 + C2H2)] in the plasma on the specific hybridized constituents (sp3 and sp2) in the C-network, optical transmission characteristics of the film, and its accomplished degree of nanocrystallinity were investigated. A substantial segment of the NCD was achieved in the DLC matrix. An optimized diamond-phase component corresponding to the minimized bond angle disorder in the matrix was accounted from the manifestation of the maxima of IDia/IG and IDia/ID simultaneous to the minimum of ID/IG ratio in Raman response, along with an allied diamond peak appearing near 1332 cm−1. The optimal DLC film at F = 0.23 revealed a wide optical band gap (Eg) of ∼3.60 eV, ∼59% sp3-hybridized C component of the diamond phase, and a significant sp3/sp2 ratio of ∼2.1. The film microstructure seemed homogeneous with uniformly distributed NCDs of average diameter ∼7.5 nm and dominant 〈111〉 crystallographic orientation. The sp3/sp2 fraction in the film matrix has been correlated directly to the IDia/IG and IDia/ID, and inversely to ID/IG ratios of the Raman data. Atomic-O, including atomic-H, remains instrumental in chemical reactions, facilitating the etching of graphitic and a-C phases while preserving the superior sp3-hybridized NCD component growing uninterruptedly in the DLC network that subsists shielded from the high-energy ion impact within secondary plasma under the shadow mask.

Revealing the Role of the Tetragonal Distortion in the Metal-Insulator Transition of Co- and Fe-Doped NiS.

Although the NiS exhibits the most widely adjustable metal-to-insulator (MIT) properties among the chalcogenides, the mechanisms, with respect to the regulations in their critical temperatures (TMIT), are yet unclear. Herein, we demonstrate the overlooked role associated with the structurally tetragonal distortion in elevating the TMIT of NiS; this is in distinct contrast to the previously expected hybridization and bandwidth regulations that usually reduces TMIT. Compared to the perspective of structure distortions, the orbital hybridization and band regulation of NiS are ∼19 times more effective adjustment in TMIT. As a result, the respective abruptions in both the electrical and thermal resistive switches across the TMIT of NiS can be better preserved in the low-temperature range (<273 K), shedding light on their optimum usage at cryogenic temperatures.

Floquet engineering of the orbital Hall effect and valleytronics in two-dimensional topological magnets.

We show that circularly polarized light is a versatile way to manipulate both the orbital Hall effect and band topology in two-dimensional ferromagnets. Employing the hexagonal lattice, we proposed that interactions between light and matter allow for the modulation of the valley polarization effect, and then band inversions, accompanied by the band gap closing and reopening processes, can be achieved subsequently at two valleys. Remarkably, the distribution of orbital angular momentum can be controlled by the band inversions, leading to the Floquet engineering of the orbital Hall effect, as well as the topological phase transition from a second-order topological insulator to a Chern insulator with in-plane magnetization, and then to a normal insulator. Furthermore, first-principles calculations validate the feasibility with the 2H-ScI2 monolayer as a candidate material, paving a technological avenue to bridge the orbitronics and nontrivial topology using Floquet engineering.

Theoretical Perspective toward Designing of 5-Methylbenzo [1,2-b:3,4-b':6,5-b″] trithiophene-Based Nonlinear Optical Compounds with Extended Acceptors.

A series of benzotrithiophene-based compounds (DCTM1-DCTM6) having D1-π1-D2-π2-A configuration were designed using a reference molecule (DCTMR) via incorporating pyrrole rings (n = 1-5) as the π-spacer (π2). Quantum chemical calculations were performed to determine the impact of the pyrrole ring on the nonlinear optical (NLO) behavior of the above-mentioned chromophores. The optoelectronic properties of the compounds were determined at the MW1PW91/6-311G(d,p) functional. Among all of the derivatives, DCTM5 exhibited the least highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) band gap (Eg) 0.968 eV with a high softness of 0.562 eV-1, and hence possessed the highest polarizability. Interestingly, transition density matrix (TDM) findings demonstrated that DCTM5 with an effective diagonal charge transmission proportion at the acceptor group supports the frontier molecular orbital (FMO) results. Additionally, the exciton binding energy values for DCTM1-DCTM6 were found to be less than that for DCTMR and thus, the effective charge transfer was examined in the derivatives. All of the derivatives exhibited effective NLO outcomes with the highest magnitude of linear polarizability ⟨α⟩, and first (βtot) and second (γtot) hyperpolarizabilities relative to the parent compound. Nevertheless, the highest βtot and γtot were obtained for DTCM1 and DTCM6, 7.0440 × 10-27 and 22.260 × 10-34 esu, respectively. Hence, through this structural tailoring with a pyrrole spacer, effective NLO materials can be obtained for optoelectronic applications.

Investigating the phase transition and properties of CaSiN2 under pressure based on first-principles calculations

In this study, we apply first-principles calculations to examine the pressure-induced phase transformation of CaSiN2 in a range of pressure of 0–100 GPa. Its pressure-induced transitions at 1.3 GPa, 15.3 GPa, and 55.8 GPa followed the order of α- CaSiN2→β- CaSiN2→α- CaSiN2→γ- CaSiN2, for α- CaSiN2→β- CaSiN2, β- CaSiN2→α- CaSiN2, and α- CaSiN2→γ- CaSiN2, respectively. The stability of the phases of CaSiN2 was confirmed based on calculations of the Born criterion of elastic stability. Its behavior transitioned in the sequence of brittle (0–1.3 GPa) → ductile (1.3–55.8 GPa) → brittle (55.8–100 GPa). The structure of its projected orbital band reflected insulating behavior by CaSiN2 under a range of pressure of 0–55.8 GPa with a direct band gap, which transformed into metallic behavior by the γ- CaSiN2 phase under pressures higher than 55.8 GPa, due to a shift in energy to higher levels around the Γ point of the N p orbitals and Si p orbitals. The Si-N bonds in CaSiN2 were found to be covalent, while ionic bonding dominated the Ca-Si and Ca-N bonds in the range of pressure of 0–100 GPa. We also investigate and discuss its mechanical properties, Vickers hardness (Hv), average sound velocity vm, and Debye temperature (θD).

Remote Insolation Forcing of Orbital‐Scale South Asian Summer Monsoon Variability

AbstractWhether the South Asian summer monsoon (SASM) is controlled by local or remote insolation at the orbital band remains uncertain. Here, we perform a transient simulation forced by Earth's orbital parameters between 400 and 350 ka BP, a period characterized by significant contrast between local and remote insolation, to identify the SASM's response to insolation forcing. Simulation results suggest that the primary driver of orbital‐scale SASM variability is the Northern Hemisphere high‐latitude June insolation, as opposed to local insolation. High June insolation in the Southern Hemisphere might reduce the SASM intensity. Remote insolation influences the SASM by altering the latitudinal thermal gradient and, consequently, the meridional position of the South Asian high (SAH). The SAH is associated with intense convection and hence drives the meridional shift of the intertropical convergence zone and the SASM rain belt. Thus, orbital‐scale SASM variability is strongly related to remote insolation forcing.

Compositing Benzothieno[3,2-b]Benzofuran Derivatives with Single-Walled Carbon Nanotubes for Enhanced Thermoelectric Performance.

Although numerous thermoelectric (TE) composites of organic materials and single-walled carbon nanotubes (SWCNTs) have been developed in the past decade, most of the research has been related to polymers without much on organic small molecules (OSMs). In this work, benzothieno[3,2-b]benzofuran (BTBF) and its derivatives (BTBF-Br and BTBF-2Br) were synthesized and their TE composites with SWCNTs were prepared. It is found that the highest molecular orbital level and band gap (Eg) of BTBF, BTBF-Br, and BTBF-2Br gradually decrease upon the introduction of electron-withdrawing Br group on BTBF. These changes significantly improve the Seebeck coefficient and power factor (PF) of OSM/SWCNT composites. An appropriate energy barrier between BTBF-2Br and SWCNTs promotes the energy filtering effect, which further contributes to the enhancement of composites' thermoelectric properties. The composites of SWCNTs and BTBF-2Br with the smallest Eg (4.192 eV) afford the best thermoelectric performance with the room temperature power factor of 169.70 ± 3.46 μW m-1 K-2 in addition to good mechanical flexibility and thermal stability. This study provides a feasible strategy for the preparation of OSM/SWCNT composites with improved thermoelectric properties.

Synthesis, DFT study, molecular docking and larvicidal activity of Chitin inhibitor alanine derived compounds

In order to obtain an effective larvicidal against A. aegypti the vectors for Dengue, Zika and Chikungunya virus, Sodium 2-{(E)-[(2-hydroxy-3-methoxyphenyl) methylidene] amino} propanoate (NaLH) ligand and its Cu(II) complexes derived from alanine amino acid with and without coligand (C1 &C2) have been synthesized. All three molecules were characterized by physicochemical techniques including FTIR, UV–Vis, proton NMR and Mass spectrum. The geometry optimization and frontier orbitals HOMO, LUMO and band gaps were calculated by using B3LYP functional and SVP basis sets for all three compounds (NaLH, complex C1 and C2). The values of HOMO/LUMO energies observed were −4.2/−1.7 eV for ligand, −5.2–3.5 eV for C1 and −5.0/−3.7 eV for C2 and corresponding values of energy gaps were 2.5 eV, 1.7 eV and 1.3 eV for NaLH, C1 and C2 respectively which increases in the following order NaLH > C1 > C2. Complex1 has been arranged in slightly distorted octahedral geometry while complex2 acquired a square pyramidal geometry. Molecular docking study of the reported larvicidal against insect acetylcholistenerase (PDB id: 6ARY) and Chitin acetylase (PDB id 5ZNT) revealed significant free energy of binding in the active site of target molecules with binding energy of −6.14 & −10.20Kcal/mol and −6.79 & −11.75Kcal/mol for C1 &C2 respectively. In addition, Larvicidal activity of complex 2 was observed with 100% mortality rate in just 2 hrs time using 1.0% concentration of larvicide. The LC50 value is 0.0015 µg/mL while LC90 value is 0.0018 µg/mL for C2. The complexes were observed to be lethal against Chitinous body layer of larvae of Aedes aegypti, the vectors for Dengue, Zika and Chikungunya virus.

Polarons and Charge Transfer in FeCr2O4 Chromite Treated by the DFT + U Method

The electronic structure of chromite (FeCr2O4 spinel) is described and the orbital ordering, band gap, and charge transfer are analyzed consistently in the framework of density functional theory taking into account strong electron correlations (DFT + U method). It is shown that the top of the chromite valence band in this model is formed by the ordered t2g orbitals of iron atoms located at tetrahedral sites, and the formation of hole polarons occurs involving just these orbitals. The nonadiabatic activation barrier determining the hole polaron transport is considered. The results of calculations of the band gap and activation energy are compared to the available experimental data.

Design of sign-reversible Berry phase effect in 2D magneto-valley material

Manipulating sign-reversible Berry phase effects is both fundamentally intriguing and practically appealing for searching for exotic topological quantum states. However, the realization of multiple Berry phases in the magneto-valley lattice is rather challenging due to the complex interactions from spin–orbit coupling (SOC), band topology, and magnetic ordering. Here, taking single-layer spin-valley RuCl2 as an example, we find that sign-reversible Berry phase transitions from ferrovalley (FV) to half-valley semimetal (HVS) to quantum anomalous valley Hall effect (QAVHE) can be achieved via tuning electronic correlation effect or biaxial strains. Remarkably, QAVHE phase, which combines both the features of quantum anomalous Hall and anomalous Hall valley effect, is introduced by sign-reversible Berry curvature or band inversion of and orbitals at only one of the K/Kʹ valleys of single-layer RuCl2. And the boundary of QAVHE phase is the HVS state, which can achieve 100% intrinsically valley polarization. Further, a k ⋅ p model unveiled the valley-controllable sign-reversible Berry phase effects. These discoveries establish RuCl2 as a promising candidate to explore exotic quantum states at the confluence of nontrivial topology, electronic correlation, and valley degree of freedom.

Two copies of spin helices with stretching pitch and compensating helicity

Persistent spin helix (PSH) manifests itself as an effective knob to tackle spin decay inevitably occurring in disordered two-dimensional electron gases. Here, for ordinary (110)-oriented two-subband GaInAs wells subjected to top and back gate voltages, we theoretically achieve adjusting the Dresselhaus terms of the two bands while meanwhile consistently pinning the system at symmetric configuration [i.e., locking the Rashba spin-orbit (SO) terms to zero], thus enabling simultaneous formation of two copies of PSHs of flexible control. Strikingly, we are able to stretch the pitch---spin density wave length---of PSH by far more than one period, enabling helix-stretch functional spin field-effect transistor (FET), with both on and off states protected by the PSH symmetry. Moreover, we attain a scenario in which the helicities of the two copies of PSHs are sufficiently compensated. This makes possible a new concept: ``orbit (band) filter,'' which resembles spin FET while with novel functionality of orbit filtering, opening up a new route towards spintronic and orbitronic combined applications.

Band topology and non-trivial surface states in type-II Dirac semi-metal X(Ni, Pd)Te2

The semi-metals having electrons near the Fermi level follow the relativistic equation of motion, and show Dirac or Weyl-type behavior. Their orbital resolved electronic bands analysis indicates the non-trivial topological states. Through the first principle methods, the electronic band structure of bulk and thin layers of transition metal dichalcogenides NiTe2 and PdTe2 are calculated and analyzed. Implementation of Hubbard corrections to the band structure indicates zero magnetization, though atoms of Ni are magnetic. Z2 invariant index is calculated for topological classification for both materials and is found to possess strong topology indicating robust topological surface states. Further, Fermi surfaces and topological surface states are computed into kz plane showing the presence of Dirac-fermions by forming of Dirac cone for PdTe2 but for NiTe2 we do not get clear evidence.