Spin-polarized Density Functional Theory Research Articles

Exploring the Mn doped BaTe alloy for spintronics and energy harvesting applications

In the present study, the ferromagnetic semiconductor behavior of Mn doped BaTe is reported along with their physical properties. The calculations are done by full potential linearized augmented plane wave (FP-LAPW) approach within spin-polarized density functional theory (SP-DFT). Formation energies were computed to satisfy the stability of reported alloys. The spin-polarization is included in the calculations to study the electronic (band structure (BS), density of states (DOS)) and magnetic characteristics. Ba1−xMnxTe elucidates the magnetic semiconductor nature with direct band gap (Eg) in both spin channels while indirect Eg (1.66 eV) is observed for pure BaTe compound. Stable ferromagnetic (FM) states are vindicated owing to the p-d hybridization which are contributors in inducing magnetic moments (μ B) at interstitial and non-magnetic sites. The optical parameters (reflectivity, absorption coefficient, refraction, optical conductivity and dielectric function) were computed within an energy range of 0–10 eV. Thermoelectric (TE) features are also figured using Boltaz-Trap code in terms of thermal and electrical conductivity, figure of merit, Seebeck coefficient and power factor. The analysis of optical parameters suggests that the considered alloys is active within visible to UV-range, having potential applications in optoelectronic, photovoltaic and thermoelectric applications.

Interatomic Interaction Models for Magnetic Materials: Recent Advances

Interatomic Interaction Models for Magnetic Materials: Recent Advances

Efficient detection of nitric oxide a biomarker associated with COVID19 via N, P co-doped C60 fullerene: a computational study.

Coronavirus (COVID-19) is a novel respiratory viral infection, causing a relatively large number of deaths especially in people who underly lung diseases such as chronic obstructive pulmonary and asthma, and humans are still suffering from the limited testing capacity. In this article, a solution is proposed for the detection of COVID-19 viral infections through the analysis of exhaled breath gasses, i.e., nitric oxide, a prominent biomarker released by respiratory epithelial, as a non-invasive and time-saving approach. Here, we designed a novel and low-cost N and P co-doped C60 fullerene-based breathalyzer for the detection of NO gas exhaled from the respiratory epithelial cells. This breathalyzer shows a quick response to the detection of NO gas by directly converting NO to NO2 without passing any energy barrier (0kcal/mol activation energy). The recovery time of breathalyzer is very short (0.98 × 103s), whereas it is highly selective for NO sensing in the mixture of CO2 and H2O gasses. The study provides an idea for the synthesis of low-cost (compared to previously reported Au atom decorated nanostructure and metal-based breathalyzer), efficient, and highly selective N and P co-doped C60 fullerene-based breathalyzer for COVID-19 detection. The geometries of N and P-doped systems and gas molecules are simulated using spin-polarized density functional theory calculations.

Investigation of magnetic exchange interactions in Cr-doped Ca0.5Sr0.5RuO3

The value of Curie temperature (T C) and resistivity for Ca0.5Sr0.5Ru1−xCrxO3 are found to increase with increase in x from 0 to 0.1. The T C increases from 38 K to 107 K. In this work, we investigate the increment using spin polarised density functional theory. The compounds exhibit Griffiths phase. Our results show that to understand the behaviour of the increase in T C , it is important to consider not only the competing super exchange and super–super exchange interactions between Ru/Cr–Ru/Cr ion pairs but also the increment in the value of the magnetic moment due to the localized character of the dopant (Cr) ion. Our results suggest that the increased resistivity with Cr doping could be due to increased scattering rate and strong on-site coulomb repulsion due to Cr doping. It is also important to note that the behaviour of T C with the Ru–O–Ru bond angle is not in line with the functional form reported for ferrites, chromites and some ferromagnetic oxides. We believe that our results will be helpful in further exploring the origin of magnetism and transport on Cr doping in perovskite ruthenates.

Exploring of Be1-xCrxSe alloys for spintronics and optoelectronic applications

In this study, spin polarized density functional theory (DFT) is implemented to predict physical characteristic of Be1-xCrxSe (x = 6.25%, 12.5%, 18.75%, 25%) compound. The electronic characteristics of pure BeSe compound show semiconductor behavior but after Cr doping BeSe elucidate half-metallic ferromagnetism (HMF) for all doping concentrations. The outcomes elucidate the total magnetic moment MTot per Cr-atom are 4.0028, 4.0027, 4.0021 and 4.0002 μB for 6.25%, 12.5%, 18.75%, 25% concentrations, respectively and the magnetism mainly originated from d-state of the impurity atom which is further ensured from the magnetic spin density. Furthermore, the optical parameters are also computed to determine the effect of doping on the material’s response to incident light of energy spanning from 0 to 10 eV. The optical study depict that the studied systems possess maximum absorbance and optical conductivity in UV-range with minimal reflection. The overall outcomes illustrate that the Cr doped beryllium selenide (BeSe) is promising material for spintronic and optoelectronic devices.

Origin of the surface facet dependence in the thermal degradation of the diamond (111) and (100) surfaces in vacuum investigated by machine learning molecular dynamics simulations

We perform machine learning molecular dynamics simulations to gain an atomic-level understanding of the dependence of the graphitization and thermal degradation behavior of diamond to the (111) and (100) surface facets. The interatomic potential is constructed using graph neural network model, trained using energies and forces from spin-polarized van der Walls-corrected density functional theory calculations. Our results show that the C(111) surface is more susceptible to thermal degradation, which occurs from 2850 K through synchronized bilayer exfoliation mechanism. In comparison, the C(100) surface thermally degrade from a higher temperature of 3680 K through the formation of sp1 carbon chains and amorphous sp2-sp3 carbon network. Due to the dangling bonds at the step edges, the stepped surfaces are more susceptible to thermal degradation compared to the corresponding flat surfaces, with the stepped C(111) and C(100) surfaces thermally degrading from 1810 K and 3070 K, respectively. We propose potential applications of this study in diamond tool wear suppression, diamond polishing, and production of graphene directly from the diamond surface.

Experimental and Theoretical Insights on the Structural, Electronic, and Magnetic Properties of the Quaternary Selenides EuPrCuSe3 and EuNdCuSe3.

Magnetic semiconductors EuPrCuSe3 and EuNdCuSe3 were obtained by using the halide flux method. Their crystal structures and magnetic properties were studied and discussed. Optical properties of the obtained selenides were studied by the means of diffuse reflectance spectroscopy, which revealed the values of 1.92/1.97 and 0.90/0.94 eV for the direct and indirect band gaps of Ln = Nd/Pr, respectively. The structural, electronic, and magnetic properties of the obtained compounds were additionally studied with spin-polarized density functional theory calculations, wherein both systems were found to be two new examples of semiconducting quaternary selenides with disperse conduction bands of Nd/Pr 5d character. The modeling showed that various magnetic orderings in the systems have subtle influences on the alignments/overlaps between the Se/Cu, Eu, and Pr/Nd bands, and that the spin-state energetics are very dependent upon the treatment of electron correlation, but a distinguishing feature in the case of ferromagnetic coupling is that the spin density on the Se atoms is maximized. Overall, the calculations are in good agreement with the experimental characterization of ferromagnetism in the bulk crystals, wherein the ferromagnetic transition occurs at temperatures of about 2.5 K for EuPrCuSe3 and about 3 K for EuNdCuSe3.

Rich essential properties of silicon-substituted graphene nanoribbons: a comprehensive computational study.

The diverse structural, electronic, and magnetic properties of silicon (Si)-substituted armchair and zigzag graphene nanoribbons (AGNRs and ZGNRs) were investigated using spin-polarized density functional theory (DFT) calculations. Pristine AGNRs belong to a nonmagnetic semiconductor with a direct bandgap of 1.63/1.92 eV determined by PBE/HSE06 functionals. Under various Si substitutions, nonmagnetic bandgaps were tuned at 1.49/1.87, 1.06/1.84, 0.81/1.45, 1.04/1.71, 0.89/1.05, and 2.38/3.0 eV (PBE/HSE06) in the single Si edge-, single Si non-edge-, double Si ortho-, double Si meta-, double Si para-, and 100% Si-substituted AGNR configurations, respectively. Meanwhile, pristine ZGNRs displayed antiferromagnetic semiconducting behavior with a spin degenerate bandgap of 0.52/0.81 eV (PBE/HSE06) and becomes a ferromagnetic semimetal in the single Si configurations or an unusual ferromagnetic semiconductor in the 100% Si configuration. Under the developed first-principles theoretical framework, the formation of quasi π (C-2pz and Si-3pz) and quasi σ (C-2s, -2pxy and Si-3s and -3pxy) bands was identified in the Si-substituted configurations. These quasi π and quasi σ bands showed weak separation, resulting in weak quasi sp2 hybridization in Si-C bonds, in which the identified hybridization mechanism was a strong evidence for the formation of stable planar 1D structures in the Si-substituted configurations. Our complete revelation of the essential properties of Si-substituted GNRs can provide a complete understanding of their chemically doped 1D materials for various practical applications.

Dual spin filtering and dual spin diode through a zigzag silicene nanoribbon

In this study, we investigate the spin-dependent electron transport properties of a zigzag silicene nanoribbon (ZSiNR) by using spin-polarized density functional theory and the non-equilibrium Green’s function method. The results show that such a ZSiNR with an FM configuration exists the perfect dual spin filtering and dual spin diode effects when the bias voltage was applied. These phenomena still exist in ZSiNRs with different widths. As the ribbon width increases, the progressively smaller bias voltage is required to trigger a polarized current. Therefore, such a ZSiNR in FM configuration is a good candidate for spintronic devices.

Enhanced photodegradation of methylene blue by Zr-doped TiO2:A combined DFT and experimental investigation

The effective mitigation of effluents in water has attracted researchers as a foremost task for addressing environmental concerns. To overcome these concerns, TiO2 (labeled as PCT-1) and Zr-doped TiO2 (labeled as PCT-2) nano catalysts are prepared by an efficient sol–gel protocol and their photocatalytic degradation performance of methylene blue (MB) is investigated. The structural integrity of nanostructures is determined by analytical tools. More than 96 % MB degradation is observed when PCT-2 is subjected to ultraviolet light for 180 min. Nanosized PCT-2 exhibits attractively advanced photocatalytic performance than PCT-1 owing to lower electron–hole pair recombination (3.02 eV) as well as superior photon capture via oxidation by photocatalytic response (confirmed through active species trapping scavenger tests). Furthermore, the results of bandgap are also confirmed by spin-polarized density functional theory (DFT) computations. The findings of this study indicate that band tuning is an attractive photocatalytic system for improving catalytic performance.

Investigation of the Structural, Mechanical, Electronic, Magnetic, and Thermoelectric Properties of Half Heusler Alloys ZrMnX (X = As, Sb, Te): A DFT‐Based Simulation

AbstractThis study investigates the structural, mechanical, electronic, magnetic, and thermoelectric properties of ZrMnX (X = As, Sb, Te) half Heusler alloys using spin‐polarized density functional theory (SPDFT) with WIEN2K code using full potential linearized augmented plane wave(FP‐ LAPW) technique. Results indicate the ferromagnetic phase’s stability over the non‐magnetic phase in all three alloys. Band structures and density of states highlight the half‐metallic nature of ZrMnX. These alloys exhibit mechanical stability, ductility, and directional properties. Magnetic moments align with the Slater–Pauling rule. Thermoelectric properties, including Seebeck coefficient, electrical and thermal conductivity, and thermoelectric figure of merit, are evaluated using semi‐classical Boltzmann theory. The Seebeck coefficient values for ZrMnX (X = As, Sb, Te) are 144.7, 123.3, and −182.6 µV K−1, respectively at 1200 K with corresponding highest figure of merit 1.0, 0.7, and 1.78. These findings suggest the suitability of these alloys for spintronic devices and high‐temperature thermoelectric applications due to their observed spin‐polarized character and high figure of merit.

First-principles investigation of structural electronic magnetic and thermodynamic properties of CdS alloyed with Co transition metal

This research work investigates the structural, electronic, and magnetic properties of Cd1–xCoxS compounds. The supercells with 16 atoms have been studied by substituting a Cd atom with a Co atom in the cubic unit cell CdS from x = 0 to x = 1 in a Zinc-Blende structure based on the first principles of spin-polarized density functional theory as implemented in the WIEN2k code. The full potential augmented plane wave method FP-LAPW (Full potential linear augmented plane wave) was used in this study to evaluate the structural properties of the compounds, the exchange–correlation term is based on the PBE-GGA (Perdew–Burke–Ernzerhof generalized gradient approximation). For other properties, such as electronic structures, densities of states, and magnetic properties, the TB-mbj GGA (Tight Binding modified Becke–Johnson) exchange potential approximation is utilized. In addition to these properties, the thermodynamic properties were added advantage to clarify their comportment as temperature variation. The analysis of the density of spin-polarized states showed the ferromagnetic character with a from x = 0.125 to x = 0.875. The calculated total magnetic moments of Cd1–xCoxS are addressed concerning the change in lattice parameters. To track the shift brought on by adding Co, we ran our calculationsfrom x = 0.125 to x = 0.875 for Cd1–xCoxS compounds. Hence, the negative energyformation indicates that our compound can be made experimentally. The material may be used for solar cell applications. In summary, our findings represent a guide for future research. The findings of this work might provide useful direction for the usage of this alloy system in a variety of device applications, For example in high-efficiency tandem solar cells, magnetic sensors, and photoconductive detector applications.

Oxygen adsorption on pristine MnBi and Ta-capped MnBi thin-films: Ab-initio study of structural and electronic properties, and magnetic anisotropy

We have studied the structural and electronic properties, as well as magnetic anisotropy in oxidized MnBi thin film with and without tantalum (Ta) atom as a capping layer. Spin-polarized density-functional theory calculations with the generalized gradient approximation (GGA) including U+J Hubbard correction, i.e., DFT+U+J have been employed. We found that the oxygen (O) atom binds more strongly to the MnBi surface when co-present with the Ta atom. We postulate that the strong binding prevents the O atoms from diffusing into the MnBi film layer. Thus, the Ta layer prevents surface oxidation by inducing strong binding of the O atoms to the Mn surface. Furthermore, in cases where molecular O2 is adsorbed on the Ta-capped MnBi, the O2 molecule fragments into two atomic components such that each of the O atoms relaxes to a different lattice sites on the MnBi film. Electronic structure analysis performed with this structure shows that the Ta atom on which one of the O atom is directly attached is weakly binded to the Mn. This makes it less feasible for the O atom to attach to MnBi surface. We conclude therefore, that two different mechanisms contrive to prevent MnBi surface oxidation. These are the strong binding of the O atom to the Mn which prevents the O diffusion into the MnBi film and the weak electronic bonding between the Ta and O which prevent the O atom from binding to the MnBi surface. Furthermore, we found that the presence of either Ta or O, or both, largely preserves the lattice structure of the MnBi film. With respect to the magnetic anisotropy energy (MAE), the presence of Ta capping layer restores the in-plane parallel magnetization of the pristine MnBi thin film after the latter’s oxidation. Where the direction of MAE is reversed from the in-plane to perpendicular, the perpendicular MAE is order of magnitude smaller than the in-plane MAE. This affirms the tendency of Ta capping layer to preserve either strongly or weakly, the direction of magnetization in oxidized MnBi. Our work provides the missing but highly crucial atomic level insights into an experimental study (M.Y. Sun et.al., Journal of Alloys and Compounds 672 (2016) 59-63) and has implications for the modeling of oxidation prevention via capping of magnetic thin film with external metallic atoms.

Catalytic mechanism of sulfur-nitrogen doping metal single-atom graphene-based catalysts for the conversion of CO2 to CH4: A computational study

The conversion of CO2 into renewable fuel (CH4) has significant environmental and economic benefits. Graphene-supported single-atom catalysts (SACs) show promise as electrocatalysts for the carbon dioxide reduction reaction (CO2RR). In this study, using spin-polarized density functional theory (DFT) calculations, we investigate the potential for converting CO2 to CH4 on the representative SACs, specifically graphene-supported TM-N-S (transition metal-nitrogen-sulfur). The results show that TM-N-S can break the scaling relationship between the adsorption energy of *CHO and *OCH2. The free energy profiles indicate that among the candidate TM-N-S SACs, Fe, Co, and Ni-N-S stand out with low overpotentials of 0.23, 0.40, and 0.39 V, respectively. Compared with the competing hydrogen evolution reaction (HER), they exhibit higher CO2 selectivity and catalytic activity. Analysis of electronic structure and charge variations reveals the origin of CO2RR activity and the binding strength between catalyst and intermediate. This work uncovers the potential mechanism of CO2RR, providing valuable insights into the conversion of CO2 to CH4 via TM-N-S catalysis and offering novel perspectives for the design and screening of efficient SACs for CO2RR.

Structural, magnetic, and optoelectronic properties of rock salt MgO co-doped with Eu-TM (TM = Cu, Ag, and Au) for spintronic and UV detector applications: SP-DFT investigations

This study analyzes how adding europium and transition metals (Cu, Ag, and Au) at a 12.5% concentration to magnesium oxide (MgO) affects its physical characteristics and potential uses. To do so, the full potential linearized augmented plane wave (FP-LAPW) method, based on spin-polarized density functional theory (SP-DFT), is used to derive the results. Wu and Cohen’s generalized gradient approximation (GGA-WC) described the exchange-correlation potential. The modified Becke-Johnson exchange potential (TB-mBJ) was also used to improve the findings of optoelectronic properties. When Eu and TM (Cu, Ag, and Au) impurities are co-doped into the nonmagnetic (NM) semiconductor MgO, the structural optimization results show that the lattice constants increase, and the bulk modulus decreases with increasing the atomic number of transition metals. The resulting dilute magnetic oxides (DMOs) are stable in the spin-polarized ferromagnetic (FM) phase, and the formation energy values confirm their stability in the [Formula: see text] cubic structure, with the lowest value belonging to Eu[Formula: see text]TM[Formula: see text]Mg[Formula: see text]O. Similarly, calculations of electronic properties using the WC-mBJ functional demonstrate that all compounds have an indirect half-metallic bandgap at L-[Formula: see text] equal to 2.53, 2.49, and 1.39 eV for Eu[Formula: see text]Cu[Formula: see text]Mg[Formula: see text]O, Eu[Formula: see text]Ag[Formula: see text]Mg[Formula: see text]O, and Eu[Formula: see text]Au[Formula: see text]Mg[Formula: see text]O, respectively. They have an integer magnetic moment of 6 [Formula: see text]. The density of states shows that at the Fermi level, the 4f-Eu, d-TM, and p-O states give rise to new energy levels. This indicates that the f–p–d hybridization provides this system with its FM properties. Also, these compounds’ dielectric function and absorption spectra are calculated and analyzed to learn more about their optical properties. The results provide insight into the optical behavior of the materials. It is observed that the co-doped compounds exhibit greater optical absorbance than their un-doped MgO counterparts do. This theoretical investigation opens the way to preparing high magnetic moment DMOs using TM and rare earth as dopants suitable for spintronic and UV devices.

Synthesis of Tridecacene by Multistep Single-Molecule Manipulation.

Acenes represent a unique class of polycyclic aromatic hydrocarbons that have fascinated chemists and physicists due to their exceptional potential for use in organic electronics. While recent advances in on-surface synthesis have resulted in higher acenes up to dodecacene, a comprehensive understanding of their fundamental properties necessitates their expansion toward even longer homologues. Here, we demonstrate the on-surface synthesis of tridecacene via atom-manipulation-induced conformational preparation and dissociation of a trietheno-bridged precursor on a Au(111) surface. The generated tridecacene has been investigated by scanning tunneling microscopy and spectroscopy (STM/STS), combined with first-principles calculations. We observe that the STS transport gap (1.09 eV) shrinks again following the gap reopening of dodecacene (1.4 eV). Spin-polarized density functional theory calculations confirm an antiferromagnetic open-shell ground-state electronic configuration for tridecacene in the gas phase. Interestingly, tridecacene's open-shell character is significantly reduced upon interaction with the Au(111) surface despite being only physisorbed. The interaction with the surface leads to a lowering of the magnetization of tridecacene, a reduced gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), compared to the gas phase, and a reduced relative energy to the nonmagnetic state, making it nearly isoenergetic. These observations show qualitatively that the influence of the Au(111) substrate on the properties of long acenes is significant, which is important for interpreting the measured STS transport gaps. Our work contributes to a fundamental understanding of the electronic properties of long acenes, confirming a nonmonotonous length-dependent HOMO-LUMO gap, and to the development of multistep tip-assisted synthesis of elusive compounds.

Electronic and Optical Properties of Mn-Doped HgSe Topological Insulator for Spintronic Devices

HgSe is a Mercury chalcogenide material of the HgX family (where X = S, Se, Te) which crystallises in the zincblende crystal phase. The electronic band structure of HgSe is indicative of a new state of matter in the condensed phase that is of great interest for fundamental physics and possibly new applications. This paper reports ab-initio calculations of the structural, electronic, magnetic, and optical properties of zincblende Mercury selenide (HgSe) doped with manganese (Mn) in the inter sites HgMnxSe, with x = 0, 0.058, and 0.117, using the framework of spin-polarized density functional theory (SP-DFT). The aim of our investigation is to discuss the different properties of this doped material in order to improve the promising new domain of spintronics with topological systems. Both the GGA + U + mBJ approach and spin–orbit coupling (SOC) are used for band structure calculations and density of states. The results show a nontrivial topological semimetal order for HgSe and a ferromagnetic topological and metallic behaviour for HgMnxSe. The frequency response of optical properties shows interesting characteristics. Furthermore, the variation with concentration x of the critical point for each of the optical parameters is similar to that of the inverted band gap.

Designed synthesis N-doped sulfonated bifunctional catalyst for efficient 5-hydroxymethylfurfural production: A pyridinic N-triggered proton-shift mechanism at basic sites

Considering the essential role of acidic/basic sites in efficient 5-hydroxymentylfurfural (5-HMF) production from cellulose, the superiority of acid-base bifunctional catalysts was unfolded. However, the lack of in-depth research on catalytic mechanism of active sites, especially the basic sites, greatly hinders its chemical utilization. Herein, N-doped sulfonated bifunctional catalysts were rationally designed. The synthesized NCS-1H catalyst exhibited outstanding activity and recyclability. Favorable 5-HMF yield of 50.0 % with 62.9 % of selectivity was obtained. Spin polarized density function theory (DFT) analysis revealed a pyridinic N-triggered proton-shift mechanism of glucose isomerization. Catalyzed by pyridinic N, the proton of glucose on C2 was shifted to O5, leading to the cleavage of C1-O1 bond. As a result, an enol intermediate was formed and converted to fructose. Compared to pyrrolic N and graphitic N, pyridinic N significantly reduced the reaction energy barrier of rate-determining step to 0.79 eV, i.e., C1-O1 bond cleavage.

Structures and reactivity of monomeric MoO[formula omitted] moieties supported on ZrO[formula omitted] (111) slab: A DFT study

Supported molybdenum oxides have been widely employed as catalysts for variety of reactions including upgrading of bio-oil via hydrodeoxygenation. Herein, we perform spin-polarized density functional theory calculations to investigate the structures and reactivity of monomeric MoOx species supported on ZrO2 in the absence and presence of hydroxyl(s). Monomeric molybdenum moieties were found to have a mono-oxo (one molybdenyl), di-oxo (two molybdenyls) or a pero-oxo (one molybdenyl and Mo coordinated to a peroxide) configuration. Based on the formation energies, we find that mono-oxo moieties are the most stable among the three. This is also true for the moieties in the presence of hydroxyls on the support. Further, the computed vibrational frequencies of a mono-oxo moiety on a hydroxylated support is a closer match to the peaks observed in experiments. A thermodynamic analysis of the molybdenum oxide moieties on a hydroxylated support indicated that the dehydroxylation is favoured at high temperatures and low partial pressures of water. On adsorption of hydrogen on the oxygen of the support, hydrogen loses its electron and reduces Mo of the monomeric moiety without making an oxygen vacancy. We studied the activity of this reduced site for deoxygenation of anisole to benzene. The overall barriers for this reaction are comparable to previously computed barriers for deoxygenation of bio-oil model compounds on an oxygen-vacant molybdenum oxide surfaces, suggesting that this may be an important mechanistic pathway during a hydro-deoxygenation process.

Isovalent dopant-vacancy clusters in silicon: Density functional theory calculations

Isovalent dopants (D) incorporated in the silicon (Si) lattice can readily associate with vacancies to form dopant-vacancy pairs. Theoretical and experimental studies have shown that vacancies (V) tent to accumulate around isovalent dopants to form DVn clusters, where D is carbon (C) germanium (Ge), tin (Sn) and lead (Pb). Using spin polarised density functional theory, we examine the lowest energy structures of D, DV and VDV (D = C, Ge, Sn and Pb) and the energies to form defects and defect clusters from point defects. The results show that substitution of Ge is thermodynamically favourable. Formation of DV and VDV clusters is endoergic for all for dopants. Binding is favourable for all clusters and even more favourable for larger dopants such Sn and Pb. The results are discussed using ionisation energy, structural parameters, Bader charges and electronic structures.