Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 8, No. 6, 2836-2842 2024 Publisher: Learning Gate DOI: 10.55214/25768484.v8i6.2570 © 2024 by the authors; licensee Learning Gate © 2024 by the authors; licensee Learning Gate * Correspondence: rasha.talal@utq.edu.iq Theoretical investigation of bonding type effect in ferrocene dimers on electric and thermoelctric proteprties Rasha Talal Jasim1*, Mohammed Deia Noori2 1,2Department of Physics, College of Sciences, University of Thi-Qar, Thi-Qar, Iraq; rasha.talal@utq.edu.iq (R.T.J.). Abstract: Thermoelectric materials possess the capacity to significantly impact worldwide energy usage by virtue of their capability to transform heat into electrical energy. However, the majority of these materials exhibit low efficiency. Currently, there are ongoing studies exploring the thermoelectric properties of molecular junctions and low-dimensional structures. These investigations aim to identify and evaluate new nanostructure systems that can overcome the existing limits. In this study, we have conducted a theoretical comparison of the electrical and thermoelectric properties of four distinct topologies of ferrocene dimers. The findings of our study indicate that the connectivity and bonding type between ferrocene dimer units play a crucial role in controlling the quantum interference (QI) and enhancing the thermoelectric properties of these molecular junctions. These structures are highly promising for use as thermoelectric enhancers and are well-suited for many thermoelectric applications. Keywords: Ferrocene, Figure of merit, Molecular junctions, Seebeck coefficient, Transmission coefficient. 1. Introduction In the last two decades, there has been substantial advancement in the domain of single-molecule electronic systems. These systems currently offer a platform for investigating fundamental characteristics of materials at the molecular or atomic level. This encompasses the examination of charge transport, molecular spintronics, and thermoelectric performance, as indicated by references [1- 6]. Various empirical and theoretical studies have been conducted to enhance and control electronic molecules [7–14] for potential utilization in nanoelectronics circuits, such as molecular wires [15], electrodes [16], wiring circuits [17], and switches [18]. Various methodologies for constructing and analyzing molecular junctions have also been devised. These studies have garnered significant attention in recent times because of their potential to develop electrical devices that are more practical and exhibit superior performance in the future [19–21]. Thermoelectricity is the phenomenon of directly converting heat into electric power. Numerous devices operate on the principles of thermoelectricity [22–24]. These devices consist of thermoelectric (TE) materials, which have been selected as a practical solution in this rapidly expanding industry since they directly convert heat into electricity [25]. Several experimental studies have been conducted to examine the molecular heat transport of these junctions. However, the ultrasmall scale of these junctions presents significant challenges. Most of the measurements are plagued by uncertainties, and many of the transport mechanisms still require further explanation and understanding. Therefore, a theoretical examination provides a solution to these challenges. Theoretical simulation allows us to improve our understanding and gain more detailed knowledge about electron transport pathways in different models of molecular junctions. Furthermore, it enables us to clarify the experimental measurements. The text provided by the user is [26]. Certain molecules possess distinctive transport capabilities and thermoelectric qualities that make them promising candidates for utilization in the development of nanoelectronic circuits in the future. Therefore, there has been substantial investigation into the thermoelectric properties of these specific 2837 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 8, No. 6: 2836-2842, 2024 DOI: 10.55214/25768484.v8i6.2570 © 2024 by the authors; licensee Learning Gate types of molecular junctions. Ferrocene is considered one of the most important molecular junctions due to its remarkable thermal and chemical stabilities, as well as its flawlessly symmetrical geometric structure. This has led to a great deal of attention in ferrocene throughout the years. The range of values is from 27 to 30. Due to the limited number of organizations worldwide with the capability to quantify the thermal conductivity of individual molecules. Hence, it is imperative to do theoretical study in order to develop, discover, and explore novel thermoelectric materials. The objective is to discover and investigate novel materials that can successfully implement these tactics in a laboratory setting. This work presents a comparative theoretical analysis of the electrical and thermometric properties of four distinct configurations of ferrocene dimers. The first structure is the TM(FeCp2) structure D1, the second is the bisferrocenylpentalenyl structure D2, the third is the biferrocene structure D3, and the last is the bisferrocenylindacenyl dithiolates structure D4 [30-35], as illustrated in Figure 1a. Figure 1. (a) Schematic illustration of the configuration of four dimer ferrocene structure D1 is TM(FeCp2), structure D2 is bisferrocenylpentalenyl, structure D3 is biferrocene, structure D4 is bisferrocenylindacenyl dithiolates (b) Molecular junction gold electrode- ferrocene dimer-gold electrode of all dimer ferrocene. 2838 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 8, No. 6: 2836-2842, 2024 DOI: 10.55214/25768484.v8i6.2570 © 2024 by the authors; licensee Learning Gate 2. Method The molecular geometry of all the ferrocone dimers depicted in Figure 1 was optimized before the junction model was constructed. The thiol anchor group was employed in Fig. 1b to secure ferrocone units to gold leads. The SIESTA [36] algorithm was utilized to conduct the geometrical optimization of all systems by incorporating Density Functional Theory (DFT). The generalized gradient approximation (GGA) was employed to calculate the exchange and correlation functions with a double-z polarized (DZP) basis set [37]. The GOLLUM algorithm was used to integrate the mean-field Hamiltonian that was derived from the converged DFT computations [38]. Quantum transport theory has been employed by the GOLLUM software to calculate the thermoelastic and electrical properties of a variety of junctions. 3. Results and Discussion To analyze the electrical and thermoelectric properties of the dimer ferrocene, the initial step is determining the transmission coefficient T(E) for each junction. These junctions are composed of a dimer of ferrocene positioned between two gold electrodes, as depicted in Figure 1b. Modifying the bond type between ferrocene dimer units leads to a change in their structural arrangement, which in turn modifies the channel for charge transport. This alteration results in the emergence of new quantum interference (QI) patterns in the transport curve. Figure 2 displays the transmission probability of the four ferrocene dimers as it varies with energy. Figure 2 clearly demonstrates that the transmission coefficients of D1 and D3, represented by the black and dashed red lines, exhibit a more uniform and consistent behavior without any distinct characteristics. In contrast, D2 and D4 display visible features in close proximity to the Fermi energy EF = 0 eV. The proximity of the resonances of D2 and D4 to the Fermi energy makes them crucial for the upcoming calculations. Figure 2. The DFT-transmission probability T(E) as a function of energy for all molecular junctions. 2839 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 8, No. 6: 2836-2842, 2024 DOI: 10.55214/25768484.v8i6.2570 © 2024 by the authors; licensee Learning Gate The corresponding electrical conductance is shown in Figure 3a. Reflecting on the peaks in the transmission coefficient curve around Fermi energy Figure 2, both D4 and D2 show higher electrical conductance than D1 and D3. Figure 3b illustrates the relationship between thermal conductivity and energy. It is evident that all systems exhibit a similar disposition, with D4 and D2 displaying a slightly greater thermal conductivity value than D1 and D3 in the vicinity of the Fermi energy. Figure 3. (a) Room temperature electrical conductance (b) Thermal conductivity as function of energy of all four ferrocene dimers. Figure 4 shows the thermopower S as a function of energy. Fig.4 shows that D2, D3, and D4 have a higher thermopower value than D1 at Fermi energy EF = 0 eV, this can be attributed to peaks around the Fermi level in the transmission coefficient curve. The highest values of thermopower occur in D2 varied between +265 μV/K (pink line) and +155μV/K in D3 (dashed red line). Figure 4. Seebeck coefficient S as a function of Fermi energy for all ferroce dimer junctions. 2840 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 8, No. 6: 2836-2842, 2024 DOI: 10.55214/25768484.v8i6.2570 © 2024 by the authors; licensee Learning Gate The most important quantity calculated is the thermoelectric efficiency ZT. The ZT is a dimensionless parameter that serves as a measure of performance [20]. The equation ZT = S^2 * G * T / κ represents the correlation between the figure of merit ZT and the electric conductance G, the square of the Seebeck coefficient S, and the thermal conductance κ. The variable ZT is directly proportional to the variables G and S squared and inversely proportional to the variable κ. Generally, to achieve a high thermopower S and ZT figure of merit, it is recommended to have properties at the Fermi level. Figure 5 illustrates the energy-related merit of the four ferrocene dimes. Due to its high electrical conductance and the presence of thermopower S near the Fermi level, D4 exhibits significant conductivity. Furthermore, D4 exhibits a high ZT value of approximately 6 at 0.0 eV, while D2 has attained a ZT value of approximately 4 at 0.0 eV. The high values of S and ZT can arise when the resonances are located near the Fermi level. Figure 5. Thermoelectric figure of merit ZT as a function of Fermi energy for all ferroce dimer junctions. 4. Conclusion In conclusion, it was investigated that the thermoelectric properties of four different configurations of ferrocene dimers placed between two gold electrodes. The results indicate that the electrical transport and thermoelectric properties of these systems can be effectively controlled by altering the bonding type between ferrocene dimer units. The resonances greatly support the S and ZT, especially when they are close to the Fermi level. The maximum value of ZT≈6 is archived in D4,and D2 shows a good ZT value with≈4. It is believed these discoveries are significant because they provide new opportunities for the transfer of thermoelectric energy in functionalized organic molecules. 2841 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 8, No. 6: 2836-2842, 2024 DOI: 10.55214/25768484.v8i6.2570 © 2024 by the authors; licensee Learning Gate Copyright: © 2024 by the authors. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). References [1] M. M. Waldrop, “The chips are down for Moore’s law,” Nat. News, vol. 530, no. 7589, p. 144, 2016. [2] S. K. Saxena, U. M. Tefashe, and R. L. McCreery, “Photostimulated near-resonant charge transport over 60 nm in carbon-based molecular junctions,” J. Am. Chem. Soc., vol. 142, no. 36, pp. 15420–15430, 2020. [3] Sakban, Raunaq H., Mohammed D. 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