BIBECHANA Vol. 20, No. 3, December 2023, 224–235 ISSN 2091-0762 (Print), 2382-5340 (Online) Journal homepage: http://nepjol.info/index.php/BIBECHANA Publisher:Dept. of Phys., Mahendra Morang A. M. Campus (Tribhuvan University)Biratnagar Enhanced electronic and magnetic performance of MoS2 monolayer via Tc & Nb impurities defect and water adsorption on impurities defected materials Hari Krishna Neupane1,∗∗, Prakash Khatri2, Arun Devkota2 Narayan Prasad Adhikari2,∗ 1Amrit Campus, Institute of Science and Technology Tribhuvan University, Kathmandu, Nepal 2Central Department of Physics, Institute of Science and Technology, Tribhuvan University, Kathmandu, Nepal ∗Corresponding author. Email: narayan.adhikari@cdp.tu.edu.np ∗∗Email: hari.neupane@ac.tu.edu.np Abstract This study examined the effect of Tc & Nb impurity atoms on MoS2 (Tc-MoS2 & Nb-MoS2), and adsorption of water molecule on impurities defected MoS2 (Tc-W-MoS2 & Nb-W-MoS2) material from first-principles calculations. By the estimation of their ground state energy and binding energy, they are stable 2D materials. From band structure and density of states (DoS) calculations, Tc & Nb impurities affect the nature of pristine MoS2. It is found that Tc-MoS2 has n-type & Nb-MoS2 has p-type semiconducting nature. Water interaction on Tc-MoS2 & Nb-MoS2 slightly changes the electronic properties and impacts the bandgap, which enhanced the electronic performance of material than that of pristine MoS2. The magnetic properties of Tc-MoS2, Nb-MoS2, Tc-W-MoS2, and Nb-W-MoS2 are analyzed and found to exhibit an uneven distribution of up-spin and down-spin states of electrons in the orbital of atoms near the Fermi level. It reflects that they have magnetic properties. The non-magnetic MoS2 material changes in to weak magnetic defected-MoS2 materials due to the presence of Tc, Nb and adsorbed water molecule. It means, impurity defects add to magnetic properties of pristine MoS2. Magnetic properties on defected MoS2 occurred due to the dominant contributions of spin states of 4d-orbital of Mo, Tc, Nb atoms, and 3p-orbital of S atoms in the structures. This study highlights the impact of Tc & Nb impurity atoms and adsorbed water molecule on impurities defected MoS2. The studied materials have potential applications in the fields of catalysis, nanoelectronics, biomedicine, and magnetic sensors on the basis of their electronic and magnetic properties. Keywords Adsorption, Defect, Fermi, Impurity, semiconducting. Article information Manuscript received: August 10, 2023; Accepted: September 1, 2023 DOI https://doi.org/10.3126/bibechana.v20i3.57470 This work is licensed under the Creative Commons CC BY-NC License. https://creativecommons. org/licenses/by-nc/4.0/ 224 http://nepjol.info/index.php/BIBECHANA narayan.adhikari@cdp.tu.edu.np hari.neupane@ac.tu.edu.np https://doi.org/10.3126/bibechana.v20i3.57470 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ Hari Krishna Neupane et al./ BIBECHANA 20 (2023) 224-235 225 1 Introduction Two-dimensional (2D) transition-metal dichalco- genides (TMDCs) are a type of compound that con- sists of a transition metal from group IV-X (e.g., Mo or W) and a chalcogen element (S, Se, or Te) arranged in the form MX2 [1]. These compounds can have a variety of properties, including metal- lic (such as VS2 and NbS2), semiconducting (such as MoS2and WS2), or insulating (like HfS2) [2, 3]. TMDCs have a structure where one layer of M atoms is sandwiched between two layers of X atoms, and these layers are held together by van der Waals (vdWs) force. Their structure is composed of a honeycomb pattern [4, 5]in which the three atomic planes (chalcogen-metal-chalcogen) stack to create the individual layers of the material [6]. The MoS2 monolayer is a semiconducting TMDs material that has Mo and S atoms stacked together in an S-Mo-S configuration, which results in a direct bandgap of 1.80 eV [5–9]. The unique properties of hexagonal TMDs materials include their atomic-scale thick- ness as well as their direct bandgap in its electronic band (wide bandgap exotic semiconductor), which can vary depending on the stacking order [3, 7, 10]. The weak interlayer forces, strong spin-orbit cou- pling, and robustness of MoS2 make it an attrac- tive material for electronic and mechanical applica- tions due to its layered structure [11–13]. Due to its high on/off current ratio and higher carrier mo- bility at room temperature, MoS2 has applications in field-effect transistors (FETs) and photodetec- tors [14, 15]. 2D semiconductors, both in the form of monolayer and multilayer, have a wide range of applications. They include usage in transistors, signal amplifiers and integrated logic circuits [16]. They also have potential uses in photocatalysts, so- lar cells, spintronics, flexible optoelectronics, na- noelectronics, nanophotonic, nanosensing, energy harvesting, photovoltaic solar cells, photocatalytic cells [17–19], DNA sequencing, biological and chem- ical sensors, lubricants, and catalytic surfaces for hydrogen storage in technology and industrial sec- tors [20,21]. The electronic properties of 2D materials can be affected by external factors such as strain, elec- tric field, pressure, temperature, doping, and de- fects. This means that the properties of TMDCs can be adjusted by controlling the environment they are in [22–25]. It is interesting to study how 2D materials like TMDCs interact with various sol- vents, such as water, due to their atomically flat surfaces which allow for different hydrophobic and long-range interactions [26, 27]. The areas around the edges and vacancies in 2D materials are highly sensitive to the adsorption of molecules, which can change the electronic and magnetic properties of the layers by distorting their arrangement [24, 28]. The way that H2O interacts with MoS2 can vary depending on where it is adsorbed [29]. The way that 2D materials interact with other materials, bio- molecules, solvents and ions is affected by the struc- ture of water at the interface [30–32]. The ability to tune the electronic structure of 2D-TMDs is made possible by the strong relationship between defects and chemical dopants in these materials, as well as the stacking of multiple monolayers [33, 34]. MoS2 based devices are used in moisture environment too, so MoS2-based devices can also be used in moist environments. However, the adsorption of water molecules on the monolayer MoS2 can lead to water- induced oxidation and the formation of Molybde- num Trioxide (MoO3), which causes the loss of lu- bricity [35, 36]. Various studies have revealed that the accumulation of hydrocarbon contaminants in the air can cause MoS2 to become more hydropho- bic over time, and this can affect the material’s electrical or structural properties [37]. Despite the amount of research on the interaction of MoS2 with water, the interactions of impurity-defected MoS2 with water have not been thoroughly examined. Understanding these interactions could lead to the development of more efficient 2D materials-based biological and chemical sensors for medical devices [38]. Crystalline structures inevitably contain de- fects, or deviations in the arrangement of atoms or ions, and are considered a necessary consequence of entropy considerations in solids [39, 40]. Imper- fections in solid materials, such as the replacement of an atom with a foreign atom or the removal of an atom from the structure, are known as impu- rity and vacancy defects respectively. These defects play a crucial role in altering and utilizing the un- desired properties of the material [41]. These de- fects can lead to the discovery of new electronic, magnetic, mechanical, and transport properties in materials. This can have potential applications in various fields including catalysis, nanoelectronics, biomedicine, magnetic sensors, and more. It is cru- cial to study the properties of 2D materials with defects and how they are affected by these imper- fections [42,43]. Previous studies have investigated the struc- tural, electronic and magnetic characteristics of a pure MoS2 monolayer [8, 9], but the effect of im- purities such as Tc, Nb on MoS2 and water ab- sorbed on impurities defected MoS2 have not been reported. The current study aims to examine the impact of the impurity atoms on MoS2 using first- principles calculations that combine spin-polarized density functional theory (DFT) method. The re- mainder of the paper is structured as follows: the methodology and computational details used in the study are discussed in Section 2, the findings, re- sults and discussion are presented in Section 3, and Hari Krishna Neupane et al./ BIBECHANA 20 (2023) 224-235 226 the final conclusions of the work are outlined in Sec- tion 4. 2 Methods and Mateials The study carried out structural optimization, elec- tronic and magnetic properties calculations using density functional theory (DFT) method [44] imple- mented in the Quantum ESPRESSO code [45] using ultra-soft pseudopotentials (USPPs). The Grimme model of USPP suggests the use of the Rappe-Rabe- Kaxiraas Joannopoulos (RRKJ) model to describe weak van der Waals (vdWs) interactions in the sys- tem. This model of USPPs includes only the chem- ically active valence electrons in the calculations, which reduces the complexity of the effects caused by the motion of non-valence electrons of an atom and its nucleus [46]. The valence electronic config- uration in H, C, Mo, O, S, Tc and Nb atoms of our system are H: 1s2; O: [He] 2s22p4; S: [Ne] 3s2 3p4; Mo: [Kr]4d5 5s1; Tc: [Kr] 4d5 5s2 and Nb: [Kr] 4d5s1 respectively. We used a (3×3) supercell struc- ture of monolayer MoS2 to perform our calculations. First, we created the unit cell of MoS2 using the XCrySDen (structure visualization software) and Quantum ESPRESSO (QE) computational tools. We have used an experimental lattice parameter of value 3.19 Å in the input file. We then converged the kinetic energy cut-off value, k-points, and lat- tice parameters. We then constructed impurity de- fects in MoS2 by replacing the central Mo atom with Nb and Tc respectively and then water molecule ad- sorbed on impurity defected MoS2 are shown in Fig. 1(a-d) respectively. The study also used a plane wave basis set and generalized gradient approxima- tion (GGA) with Perdew, Burke, and Ernzer (PBE) to incorporate electronic exchange and correlation (XC) potential in the calculations [47]. The plane wave basis set is used to implement kinetic energy cutoff and charge density cutoff in the calculations. The kinetic energy cutoff used is 35 Ry and the charge density cutoff is 10 times the kinetic energy cutoff, which is 350 Ry, for all systems using USPPs for plane wave expansion. A (8×8×1) k-mesh gen- erated using the Monkhorst-Pack (M-P) scheme is used to integrate the Brillouin Zone (BZ) during self-consistent calculations and structure optimiza- tion in the first irreducible Brillouin Zone [48, 49]. The calculations are stopped when the total energy and force reached a threshold of 10-4 Ry and 10- 3 Ry/Bohrs respectively to ensure accurate results. The optimization of all structures is done using the Broyden-Fletcher-Goldfarb-Shanno (BFGS) [50] al- gorithm until the change in total energy is less than 10-4 Ry and the force is less than 10-3 Ry/Bohrs between two consecutive scf iterations. The cal- culations used a small broadening width of 0.001 Ry using the Marzarri-Vanderbilt (M-V) smearing method to ensure the accuracy of the results [51]. The "david" diagonalization method with a mix- ing factor of 0.6 is chosen for self-consistency. In order to study magnetic properties, spin-polarized density of states (DoS) and partial density of states (PDoS) calculations are performed. The systems are relaxed by using optimized values of kinetic en- ergy cutoff, charge density cutoff, k-points, and lat- tice parameters. The self-consistent total energy calculations are done after the relaxation. The band calculations are done by selecting 100 k-points along the high symmetry points in the reciprocal lattice. These k-points are the sampling points in the first Brillouin Zone of the reciprocal lattice. Before cal- culating the density of states (DoS) and partial den- sity of states (PDoS), non-self-consistent (nscf) cal- culations are done using an automatic denser mesh of (16×16×1) k-points, with a verbosity setting of "high" and an occupation setting of "tetrahedra". 3 Results and Discussion In this section, we discussed in detail about the structural, electronic, and magnetic properties of pristine MoS2, Tc & Nb impurities defected MoS2 materials, and water adsorption on impurities de- fected MoS2 materials. The analysis is based on spin-polarized DFT method of calculations. 3.1 Structural Analysis In this section, we have discussed the structural properties of pristine MoS2, Nb & Tc impurities defected MoS2, and water adsorbed on impurities defected MoS2 materials. Firstly, we have prepared unit cell of MoS2 and check its stability by calcu- lating its ground state energy and binding energy, it is found to be stable 2D material. After that, we have prepared (3×3) supercell structure of MoS2 by extending unit cell along x-and y-axis, which is used for further calculations. So, we examined the stability of (3×3) supercell structure of MoS2 by estimating its ground state energy -1741.61 Ry and binding energy 6.83 eV, and found that it is stable material. This estimated binding energy value is comparable with reported value of other stable 2D materials [52, 53]. The binding energy of MoS2 is found by using equation (1) [24]; (Eb)Mo−S2 = [EMoS2 −NEMo −N ′Es]/N” (1) where, (Eb)Mo−S2 is the binding energy per Mo- S2 pair, EMoS2, EMo & ES are the ground state energy of MoS2, single Mo & single S atoms respec- tively, N & N’ respectively represent the number of Mo atom & S atom present in supercell structure, N” indicates the total number of atoms present in supercell structure. Moreover, we have constructed Tc impurity defected MoS2 (Tc-MoS2) material by Hari Krishna Neupane et al./ BIBECHANA 20 (2023) 224-235 227 replacing Mo sites atoms from stable (3×3) super- cell structure of MoS2, and then relax calculations are done. The minimum ground state energy of value -1774.07 Ry and maximum binding energy of value 7.32 eV are obtained at the center position of Mo atom of Tc-MoS2, is shown in Fig. 1(a). This value is close with reported value of other 2D ma- terials [52, 53]. Similar procedure is done for the fabrication of Nb impurity defected MoS2 supercell structure (Nb-MoS2). The estimated ground state energy and binding energy of Nb-MoS2 are found to be -1711.97 Ry & 6.42 eV respectively. The esti- mated binding energy of Nb-MoS2 agrees with re- ported value of other 2D martials [52, 53]. Hence, Nb-MoS2 is a stable 2D material, is shown in Fig. 1(b). The binding energy of Tc-MoS2 and Nb-MoS2 are obtained by using equation (2) [24]; (Eb)Tc/Nb−Mo−S2 =[ ETc/Nb−MoS2 −NEMo −N ′ES −N ′′ETc/Nb ] /N ′′′ (2) where, (Eb)Tc/Nb−Mo−S2 is the binding energy per Tc-MoS2 pair, ETc/Nb−MoS2, EMo, ETc/Nb & ES are the ground state energy of Tc/Nb-MoS2, single Mo, single Tc or Nb & single S atoms respectively, N, N’ & N” respectively represent the number of Mo atom, number of S atom, and number of Tc or Nb atom present in impurities defected MoS2 super- cell structure, N” ’ denotes total number of atoms present in defected supercell structures. Furthermore, water molecule is adsorbed on dif- ferent positions at 2.45 distance above the sur- face of Tc-MoS2 & Nb-MoS2, it is found that ad- sorbed water molecule (i.e., physio-adsorption) is at 2.45 distance vertically from the center position of MoS2 are more stable materials, which are shown in Fig. 1(c-d). This is because they have minimum ground state energies (-1810.08 Ry of Tc-W-MoS2 & -1747.98 Ry of Nb-W-MoS2 respectively), and maximum binding energies (7.89 eV of Tc-W-MoS2 & 6.98 eV of Nb-W-MoS2 respectively) than other positions of adsorbed water molecule on defected MoS2. These binding energies are fairly agree with reported value of other stable 2D materials [52,53]. We have also estimated the adsorption energy of water molecule with Tc-MoS2 & Nb-MoS2 by us- ing equation (3), and found to be 2.17 eV & 2.08 eV respectively. They are comparable with the re- ported values of water adsorption on 2D materi- als [9, 25, 27]. Hence, water adsorbed defected ma- terials are stable 2D materials. Ea = ETc/Nb−MoS2 + EH2O − ETc/Nb−W−MoS2 (3) where, Ea is the adsorption energy of water molecule with Tc-MoS2 or Nb-MoS2 materials, ETc/Nb−MoS2 & EH2O, are the ground state en- ergy of Tc-MoS2 or Nb-MoS2 and adsorbed water molecule respectively. From the estimation of bind- ing energies of Tc-MoS2, Nb-MoS2, Tc-W-MoS2 and Nb-W-MoS2 materials, we concluded that Tc impurity defected MoS2 are more compact than Nb impurity defected MoS2 structure. 3.2 Electronic and Magnetic Properties Solid materials are made up of a large number of atoms, each with discrete energy levels for their electrons. When two similar atoms are brought to- gether, their atomic orbitals overlap and split into distinct energy levels for the molecule, forming a continuous range of energy known as an energy band. Understanding the band structure and den- sity of states (DoS) of a solid material provide in- sight into its electronic properties. Magnetic prop- erties of materials are explored by analyzing of their density of states (DoS) and partial density of states (PDoS). Therefore, electronic and magnetic prop- erties of Tc & Nb impurities defected MoS2 mate- rials (Tc-MoS2 & Nb-MoS2), and water adsorbed on Tc & Nb impurities defected MoS2 materials (Tc-W-MoS2 & Nb-W-MoS2) are studied by ana- lyzing their band structure, DoS and PDoS plots. The band structures of Tc-MoS2, Nb-MoS2, Tc-W- MoS2 and Nb-W-MoS2 are shown in Fig. 2(a-d) respectively. To understand the electronic properties of Tc- MoS2, Nb-MoS2, Tc-W-MoS2 and Nb-W-MoS2 ma- terials, band structure and DoS calculations are performed. For that, we have chosen first Bril- louin Zone of the reciprocal lattice. The x-axis of the band structure plot represents the high sym- metric points Γ-M-K-Γ of the first Brillouin Zone, with the -center being one of these points, and the y-axis corresponds to energy values. A total of 100 k-points are selected along these high symme- try points, which define a sampling path and ir- reducible region within the Brillouin Zone. In an ideal condition where the crystal is not under non- uniform strain or has imperfections. The repetition of the sampling path will cover the entire space of the Brillouin Zone. The band structure diagrams also have a horizontal dotted line, which represents the Fermi energy level. As seen in the band struc- ture of Tc-MoS2, band states of conduction band are moving closer to the Fermi energy level than that of valence band due to the rearrangement of spin states of electrons in the 3s, 3p orbitals of S atoms with 4d, 5s orbitals of Tc atom in struc- ture. Hence, number of charge carriers in conduc- tion band are greater than that in the valence band. It reveals that Tc-MoS2 is a n-type semiconducting material having direct bandgap energy 1.01 eV at Hari Krishna Neupane et al./ BIBECHANA 20 (2023) 224-235 228 (a) (b) (c) (d) Figure 1: (Colour online) Supercell structure of (a) Tc impurity defect on MoS2 (Tc-MoS2 ), (b) Nb impurity defect on MoS2 (Nb-MoS2 ), (c) water adsorbed on Tc impurity defected MoS2 (Tc-W-MoS2 ), and (d) water adsorbed on Nb impurity defected MoS2 (Nb-W-MoS2 ). (a) (b) (c) (d) Figure 2: (Colour online) band structure plots of; (a) Tc-MoS2, (b) Nb-MoS2, (c) Tc-W-MoS2 and (d) Nb-W-MoS2. In figures, the horizontal dotted line represents the Fermi level, and the vertical dotted line intersects at high symmetry points. Hari Krishna Neupane et al./ BIBECHANA 20 (2023) 224-235 229 Γ-point. This result is deviating from the prop- erties of pristine MoS2 [5–7], due to the presence of Tc impurity defects. We have estimated the bandgap energy of Nb-MoS2 material by the anal- ysis of it band structure calculations and found di- rect bandgap energy 1.10 eV in between the conduc- tion band minima and valence band maxima at high symmetry Γ-point. Band states of valence band lies closer to the Fermi energy level than the band states of conduction band. This is because unpaired ar- rangement of spin states in the 3s, 3p orbitals of S atoms with 4d, 5s orbitals of Nb atom in structure. We concluded that Nb-MoS2 is a p-type semicon- ductor material. This property is different than of pure MoS2 [6,7], which is attributed due to the pres- ence of Nb impurity defects in Nb-MoS2. We have also analyzed the density of states (DoS) plots of Tc-MoS2 & Nb-MoS2 materials are shown in Fig. 3(a-b) respectively. It is found that distributed up- spin and down-spin states open bandgap energy due to the presence of unpaired spin states in the or- bital of Tc & Nb atoms with S atoms respectively in structures. It also confirmed that Tc-MoS2 is a n-type and Nb-MoS2 is a p-type semiconductor ma- terial. From the analysis of above calculations, we concluded that impurity defects enhanced the elec- tronic conductivity in materials. Semiconducting materials have wide applications due to their reli- ability, compactness and low cost; they are having probable future. Thus, p-type and n-type semicon- ductors find a wide variety of applications in the fields of memory, sensing, electronic, spintronic, op- toelectronic devices [38,42,43]. Electronic properties of material are affected due to presence of moisture [25, 32]. So, we have investigated the electronic properties of water ad- sorbed on impurities defected MoS2 through band structure and DoS plots. The band structures of Tc-W-MoS2 & Nb-W-MoS2 are shown in Fig. 2(c- d) respectively. In the band structure of Tc-W- MoS2, a direct bandgap of 1.13 eV is observed at -point. Its Fermi energy level being closer to the conduction band, which indicates that Tc-W-MoS2 exhibits n-type semiconductor. The bandgap en- ergy of Tc-W-MoS2 has slightly greater value than that of Tc-MoS2 material because adsorbed water molecule reduces binding energy (losses lubricity). It is observed that band states are slightly repelled towards conduction band from Fermi energy level in band structure is shown in Fig. 2(c). This is also confirmed by the analysis of its DoS plot is shown in Fig. 3(c). In DoS plot, bandgap energy is computed in between upper level of valence band and lower level of conduction band of distributed up- and down-spin states of electrons in the orbital of atoms present in the material. Furthermore, we have computed the bandgap energy of Nb-W-MoS2 material on the basis of band structure and DoS plots, are shown in Fig. 2(d) & 3(d) respectively. The band structure of Nb-W-MoS2 reveals a di- rect band gap of 1.23 eV at Γ-point, which cou- pled with the Fermi energy being positioned near the valence band, indicates that Nb-W-MoS2 has p-type of semiconducting properties. This obtained result is slightly deviated from the semiconducting behavior of pure MoS2, which is due to the pres- ence of adsorbed water molecule and Nb impurity defect on MoS2. To confirm the predicted nature of Nb-W-MoS2, we have analyzed the DoS of it and found that distributed up- and down-spin states are appeared near the valence band is shown in Fig. 3(d). This confirmed that it has p-type semicon- ducting properties. Water molecule can interact with impurities, altering their electronic and chem- ical states and subsequently modifying the band structure, and hence inflate the electronic proper- ties than that of pristine MoS2. Additionally, water adsorbing on the surface of MoS2 can form a thin layer of water molecules and influence the electronic properties of the material. This can result in the creation of new energy levels leading to new elec- tronic states and modifications to the bandgap en- ergy. Effect of impurities (Tc & Nb) defect on pris- tine MoS2 and adsorbed water molecule on impuri- ties defected MoS2 initiate to switch in band struc- tures and DoS plots. As a result, Fermi energy, Fermi shift, total ground state energy, bandgap en- ergy, and binding energy of defected materials have changed than that of pristine form, they are pre- sented in Table-1. The reason of shifting band states in band and DoS from pristine to defected systems are; H atom has one unpaired up-spin elec- tron in 1s orbital, O atom has paired spins in 2s orbital and paired electrons in 2px sub-orbital, and unpaired electrons in 2py and 2pz sub-orbitals. The Mo atom has one unpaired up-spin electron in 5s or- bital and one in 4d orbital with sub-orbitals 4dxy, 4dxz, 4dyz, 4dx2−y2 , 4dz2 . Tc atom has paired spins in 5s orbital and one unpaired up-spin electron in 4dxy, 4dxz, 4dyz, 4dx2−y2 & 4dz2 sub-orbitals. Nb atom has one unpaired up-spin electron in 5s or- bital, one unpaired electron in 4dxy, 4dxz, 4dyz & 4dx2−y2 and one vacant in 4dz2 sub-orbital. The S atom has paired spins in 3px sub-orbital and one unpaired up-spin electron in 3py & 3pz sub-orbitals. These different electronic configurations affect the electronic and magnetic properties of materials. The magnetic properties of materials can be evaluated by analyzing their density of states (DoS) and partial density of states (PDoS). These plots provide insight into the distributions of electrons with up- and down-spins within the material. When the distributions are symmetrical, meaning that the number of up- and down-spins of electrons are equal, magnetic moments of the electrons canceled Hari Krishna Neupane et al./ BIBECHANA 20 (2023) 224-235 230 out, resulting in non-magnetic properties. However, when the distributions are asymmetrical, there are more up- or down-spins of electrons, it leads to a net magnetic moment, resulting in magnetic prop- erties. This occurs when electrons of the atoms are not paired, meaning the presence of unpaired up- and down-spins of electrons in the atomic orbitals create certain magnetic moment, leading to mag- netic properties of the material. In other words, the DoS and PDoS calculations of spin-polarized systems reveal the distributions of electrons with opposite spins in the material. If the number of electrons with opposite spins are equal, the mate- rial is non-magnetic. But, if the distributions are asymmetrical, the material has magnetic proper- ties. The reason is that electrons with opposite spins can pair up, which cancels out their magnetic moments. But, if there are more electrons with one spin direction, the material will have a net magnetic moment, making it magnetic. The PDoS plot of Tc- MoS2, Nb-MoS2, Tc-W-MoS2 and Nb-W-MoS2 are presented in Fig. 4(a-d) respectively. DoS plots (Fig. 3(a-d)), and PDoS plots (Fig. 4(a-d)) come up with the information’s of dis- tributed spin states in electronic orbitals of atoms present in the materials. The DoS plots of con- sidered materials give insight into how the impu- rities and adsorbed water molecule affect the elec- tronic and magnetic properties of MoS2. Hence, DoS used to understand how the defects and ad- sorbed water molecule influenced the electronic and magnetic properties of materials. The detail in- vestigation of magnetic properties of Tc-MoS2, Nb- MoS2, Tc-W-MoS2 and Nb-W-MoS2 materials, we have analyzed PDoS plots. In PDoS analysis, we especially focused the impact of distributed elec- tronic spin states in the orbitals of atoms present in the materials. It shows how the electrons are spread among different orbitals and how impuri- ties and water exposure affect these distributions, providing a deeper understanding of how these fac- tors affect the magnetic properties of materials. In DoS & PDoS plots of Tc-MoS2, Nb-MoS2, Tc-W- MoS2 and Nb-W-MoS2, we found that the distri- butions of up-spin and down-spin electronic states near the Fermi level are asymmetrical. We deter- mined the net magnetic moment arising from up- spin and down-spin of electrons in each orbital of the constituent atoms. Magnetic moment in the 4p, 4d & 5s orbitals of Mo atom have 0.03 µB /cell, 0.11 µB /cell & 0.00 µB /cell; 3s & 3p orbitals of S atoms have 0.00 µB /cell & 0.05 µB /cell; and 4p, 4d & 5s orbitals of Tc atom has -0.01 µ B /cell, -0.03 µB /cell & 0.00µB /cell values in Tc-MoS2 material. Total magnetic moment of Tc-MoS2 is found to be 0.15 µB /cell, and the magnetic mo- ment based on integrated density of states (IDoS) is also estimated to be 0.15 µB /cell. The magnetic moment generated in Tc-MoS2 is mainly due to the 4d orbital of Mo, 3p orbital of S, and 4d orbital of Tc atoms. Thus, Tc-MoS2 is considered a magnetic material. The magnetic properties of Nb-MoS2 are investigated by the analysis of its PDoS plot. It is determined that the 4p, 4d & 5s orbitals of Mo atoms contributed 0.01 µB /cell, 0.09 µB /cell, & 0.00 µB /cell magnetic moments respectively. Addi- tionally, the magnetic moment carried out by 3s & 3p orbitals of S atoms have 0.00 µB /cell & 0.01 µB /cell; 4p, 4d & 5s orbitals of Nb atoms have -0.02 µB /cell, -0.08 µB /cell & 0.00 µB /cell respectively. Total magnetic moment of Nb-MoS2 is found to be 0.01 µB /cell. The same value of magnetic moment of Nb-MoS2 is determined by integrated density of states (IDoS) calculation. The dominant contribu- tion of magnetic moment by 4d orbital of Mo, 3p orbital of S, and 4d orbital of Nb atoms in Nb-MoS2. Hence, Nb-MoS2 is a weak magnetic material. Table 1: Bandgap energy (Eg), Fermi energy (Ef), Fermi energy shift (Es), total ground state energy (Et), and binding energy (Eb) of MoS2, Tc-MoS2, Nb-MoS2, Tc-W-MoS2, and Nb-W-MoS2 materials. Materials Ef (eV) Eg (eV) Es (eV) Et (Ry) Eb (eV) MoS2 -1.89 1.80 - -1741.61 6.83 Tc-MoS2 -0.83 1.01 1.06 -1774.07 7.32 Nb-MoS2 -2.26 1.10 -0.37 -1711.97 6.42 Tc-W-MoS2 -1.01 1.13 0.88 -1810.08 7.89 Nb-W-MoS2 -2.42 1.23 -0.53 -1747.98 6.98 Hari Krishna Neupane et al./ BIBECHANA 20 (2023) 224-235 231 (a) (b) (c) (d) Figure 3: (Colour online) DoS plots of (a) Tc-MoS2, (b) Nb-MoS2, (c) Tc-W-MoS2 and (d) Nb-W-MoS2. In figures, horizontal dotted line separates the spin states, vertical dotted line indicates the Fermi level, and inset represents the DOS plots large range of energy level. (a) (b) (c) (d) Figure 4: (Colour online) (a) PDoS plot of individual up-spin and down-spin states of electrons in the orbitals of Mo, S & Tc atoms of Tc-MoS2 material, (b) PDoS plot of individual up-spin and down-spin states of electrons in the orbitals of Mo, S Nb atoms of Nb-MoS2 material, (c) PDoS plot of individual up-spin and down-spin states of electrons in the orbitals of Mo, S, Tc, H O atoms of Tc-W-MoS2 material, and (d) PDoS plot of individual up-spin and down-spin states of electrons in the orbitals of Mo, S, Nb, H & O atoms of Nb-W-MoS2. In figures, horizontal dotted line separates the spin states, vertical dotted line indicates the Fermi level, and inset represents the PDoS plots of large-scale energy range. Hari Krishna Neupane et al./ BIBECHANA 20 (2023) 224-235 232 Table 2: Total magnetic moment (µ) of Tc-MoS2, Nb-MoS2, Tc-W-MoS2, and Nb-W-MoS2 materials obtained by asymmetrically distributed up-spin and down-spin of electrons in various orbitals of different atoms. Orbitals / Materials Tc-MoS2 Nb-MoS2 Tc-W-MoS2 Nb-W-MoS2 µ of 4p-Mo 0.03 0.01 0.03 0.00 µ of 4d-Mo 0.11 0.09 0.12 0.08 µ of 5s-Mo 0.00 0.00 0.00 0.00 µ of 3s-S 0.00 0.00 0.00 0.00 µ of 3p-S 0.05 0.01 0.03 0.01 µ of 4p-Tc -0.01 - 0.01 - µ of 4d-Tc -0.03 - -0.04 - µ of 5s-Tc 0.00 - 0.00 - µ of 4p-Nb - -0.02 - 0.00 µ of 4d-Nb - -0.08 - -0.07 µ of 5s-Nb - 0.00 - 0.00 µ of 2s-O - - 0.00 0.00 µ of 2p-O - - 0.00 0.00 µ of 1s-H - - 0.00 0.00 Total (µ) µB/cell 0.15 0.01 0.15 0.02 Furthermore, we have estimated the magnetic properties of Tc-W-MoS2 and Nb-W-MoS2 materi- als by interpretating their PDoS plots. The mag- netic properties of Tc-W-MoS2 are predicted by the estimation of distributed electronic spin states in the individual orbital of each atom present in the structure. The 4p, 4d 5s orbitals of Mo atoms have magnetic moments 0.03 µB /cell, 0.12 µB /cell 0.00 µB /cell respectively in structure. Also, 3s 3p or- bitals of S atoms have magnetic moments 0.00 µB /cell 0.03 µB /cell; and 4p, 4d 5s orbitals of Tc atom has magnetic moments 0.01 µB /cell, -0.04 µB /cell 0.00 µB /cell respectively. Similarly, we have estimated the magnetic moment generated by 2s 2p orbitals of O atom have values 0.00 µB /cell 0.00 µB /cell; and 1s orbital of H has value 0.00 µB /cell. The total magnetic moment of Tc-W-MoS2 is obtained 0.15 µB /cell. We also have estimated the magnetic moment 0.15µ B /cell based on integrated density of states (IDoS). The magnetic moment in Tc-W-MoS2 is mainly created by the dominant ef- fect of 4d orbital of Mo, 3p orbital of S, and 4d orbital of Tc atoms. Therefore, Tc-W-MoS2 is con- sidered to be a magnetic material. In Nb-W-MoS2 , the magnetic moment is observed in 4p, 4d, 5s or- bitals of Mo atoms have 0.00 µB /cell, 0.08 µB /cell 0.00 µB /cell respectively. The magnetic moments given by 3s 3p orbitals of S atoms have values 0.00 µB /cell 0.00 µB /cell respectively. The 4p, 4d 5s orbitals of Nb atom has magnetic moments of 0.00 µB /cell, -0.07 µB /cell 0.00 µB /cell; and 2s & 2p orbitals of O has magnetic moments of 0.00 µB /cell 0.00 µB /cell, while the 1s orbital of H atom has a magnetic moment of value 0.00 µB /cell. The total magnetic moment of Nb-W-MoS2 is found to be 0.02 µB /cell. Magnetic moment of Nb-W-MoS2 also estimated through integrated density of states (IDoS), and found to be 0.02 µB /cell. The main source of magnetic moment in Nb-W-MoS2 is 4d orbitals of Mo, 4d orbitals of Nb, and 3p orbital of S atoms in the structure. Thus, Nb-W-MoS2 is weak a magnetic material. From the above calcu- lations of magnetic moment in the materials, we found that impurity atoms on MoS2 , and adsorbed water molecule on impurities defected MoS2 inten- sified the magnetic properties in the materials. The detail calculations of magnetic moment of Tc-MoS2 , Nb-MoS2 , Tc-W-MoS2 and Nb-W-MoS2 materi- als by the analysis of individual electronic orbital of atoms are given in Table-2. 4 Conclusions Structural, electronic, and magnetic properties of Tc-MoS2, Nb-MoS2, Tc-W-MoS2 and Nb-W-MoS2 materials have been explored by spin-polarized den- sity functional theory (DFT) method with van der Waals (vdWs) corrections (DFT-D2) approach through computational tool Quantum ESPRESSO. It is found that Tc-MoS2, Nb-MoS2, Tc-W-MoS2 and Nb-W-MoS2 are stable materials. The na- ture of materials has been studied through their band structure and density of states (DoS) calcula- tions, and the result showed that all materials have narrow bandgap semiconducting properties. The bandgap energy of Tc-MoS2, Nb-MoS2, Tc-W-MoS2 and Nb-W-MoS2 have values 1.01 eV, 1.10 eV, 1.15 eV and 1.23 eV respectively. The electronic band states of conduction band are appeared close to the Fermi energy level of Tc-MoS2 Tc-W-MoS2, and hence they are n-type semiconductor materials. On the other hand, band states of valence band are ap- Hari Krishna Neupane et al./ BIBECHANA 20 (2023) 224-235 233 peared near the Fermi energy level than the band states of conduction band in band structure and DoS plots of Nb-MoS2 Nb-W-MoS2 materials. It reflects that they have p-type semiconducting prop- erties. The presence of impurities in MoS2 and ad- sorbed water molecule on impurities defected MoS2 affects the semiconducting behavior of pure MoS2 by shifting the band states with respect to Fermi energy level. Band structure calculations and DoS analysis revealed that the impact of water molecules on the surface of MoS2 can alter its electronic prop- erties, leading to the creation of new energy levels and modifications to the bandgap, resulting in new electronic states. Magnetic properties of considered materials are studied on the basis of their density of states (DoS) and partial density of states (PDoS) calculations, and found that all materials have mag- netic properties. Magnetic moment of materials is developed due to presence of unpair electronic spin states in the individual orbitals of atoms present in the material. The estimated magnetic moment of Tc-MoS2, Nb-MoS2, Tc-W-MoS2 and Nb-W-MoS2 have values 0.15 µB /cell, 0.01 µB /cell, 0.15 µB /cell 0.02 µB /cell respectively. The significant values of magnetic moment are given in materials due to the presence of unpaired spin state in the 4d orbitals of Mo atoms, 3p orbital of S atoms, and 4d orbitals of Tc Nb atoms. Hence, electronic and magnetic properties are enhanced in the ma- terials due to the presence of impurity atoms on MoS2 and adsorbed water molecule on impurities defected MoS2. References [1] M. Chhowalla, H. S. Shin, G. Eda, L. J. Li, K. P. Loh, and H. Zhang. 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