small clusters in fullerene (C60) on electronic and

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Effect of encapsulation (Ru & Pd) small clusters in fullerene (C60) on electronic and magnetic properties: DFT Rana. O. Abdaljalil, and Nibras. M. Umran

Citation: AIP Conference Proceedings 1888, 020001 (2017); doi: 10.1063/1.5004278 View online: http://dx.doi.org/10.1063/1.5004278 View Table of Contents: http://aip.scitation.org/toc/apc/1888/1 Published by the American Institute of Physics

Effect of Encapsulation (Ru & Pd) Small Clusters in Fullerene (C60) on Electronic and Magnetic Properties: DFT Rana. O. Abdaljalil1,a) , Nibras. M. Umran2,b) 1)

2)

Department of physics, College of Science, University of Al-Mustansiryia, 10052, Baghdad, Iraq Department of physics, College of Science, University of Kerbala, 56001, Karbala, Iraq a)

b)

[email protected] Corresponding author:[email protected]

Abstract. We have done a systematic study of structural and electronic, to describe the Interaction between various atoms doped inside C60 by using Density functional theory (DFT) . The foresee for carbon doping, modifies the electronic properties of fullerenes. We optimized the Run@C60 and Pdn@C60 (n=1-4) complexes, we found that endohedral metallofullerenes are stable. As well, we investigated binding energy, ionization potential, and energy gap of Ru and Pd encapsulate fullerenes. Where observed the effect modified by endohedral metallofullerenes makes C60 more reactive. Also the presence of the magnetic moment in metallofullerenes using Mulliken charge analysis.

INTRODUCTION The doping function modification in the creation the fundamental of electronics and tailoring at will the properties of materials. Fullerenes attracted substantial attention due have been characterized of capability in products three different types of doping, whereas the types of doping depended on the position of dopants in C60 [1]. In endohedral doping, a dopant is assimilation within C60 cage shell. While exohedral fulelerens represents an external dopant for fullerene shells. The third type of doped, a substitutional doping where some carbon atoms of C60 cage are replaced by dopants atoms [2]. The three different doping configurations can be achieved depending on the dopant species and the production technique [3, 4]. One interesting aspect of fullerene cages is the existence of a cavity large enough to contain an atom or a small molecule. In the last years, an increasing variety of species have been endohedral metallofullerenes, being interesting candidates for the constructing new materials [5-7]. Each carbon atom in the fullerene cage possesses, having four valence electrons in the congruent system, due making the possibility of correlation of each carbon atom with three nearest neighbor atoms in fullerene shells. So, it is foreseeable that C60 should be a van der Waals nonconductor (semiconductor) [8]. Hence, for transfer charge to band a conducting molecule in fullerene, determine some species of doping necessary to equip the charge transfer to move the Fermi level for a band of conducting states [2]. Endohedral metallofullerenes, π-orbitals of atomic is In charge of interacts with the orbitals of the dopant of the shell during the space inside C60 structure [9]. It is well known that both Ru and Pd belong to the horizontal line of the same group transition of elements in the periodic table, but their chemistry is very different, add they have orbitals spd4, that give bonding characteristics of carbon give rise to novel forms starting from the well-known planar graphite and tetrahedral diamond to ‘spherical’ fullerenes and cylindrical nanotubes [10]. On the other hand, Ru and Pd prefers only tetrahedral bonding due to its larger core. Both carbon based nanostructures such afullerenes and nanotubes as well as Ru based nanostructures have potential technological applications. In theoretical research, the first principles studied of Ruthenium as an endohedral dopant in buckminsterfullerene has been carried out using (DFT), the interaction between Ru and C atoms in different conformations can be explained in terms of Mulliken analysis [11], also the density functional theory has been used to compute the geometries, electronic structure and magnetic properties of free-standing ruthenium and rhodium

6th International Conference and Workshops on Basic and Applied Sciences AIP Conf. Proc. 1888, 020001-1–020001-6; https://doi.org/10.1063/1.5004278 Published by AIP Publishing. 978-0-7354-1571-3/$30.00

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clusters. We can expect that nanoscale carbon– ruthenium composite structures may exhibit novel properties due to the large surface area and quantum size effect. There is also a study of the hydrogen storage capabilities of Pd exohedral doped C60 fullerene were investigated by using DFT Calculations. Two types of reactions, rarely reversible and Irreversible, were characterized in terms of DOS, pairwis and non-pairwise additivity, statistical thermodynamic stability, proton magnetic resonance spectra and electrophilicity [12]. As studied practically, Pd doped multiwalled carbon nanotubes (MWCNTs) have been fabricated using chemical vapor deposition techniques in existence of catalyst, and Pd nanoparticles was dispersed on it by wet impregnation and polyol methods. The hydrogen absorption study confirmed that Pd doped MWCNT's store higher amount of hydrogen compared to the bare CNT's. More interestingly the Pd doped CNT prepared by polyol method shows higher hydrogen storage capacity than samples prepared by conventional wet impregnation method [13]. This has given rise to attention recently doped carbon by ruthenium and Palladium complex nanostructures [14] which have magnificent potential for applications in nonlinear electronic component, memory devices and other applications. Fullerene molecule have empty space can use to storage atoms or small molecule of materials with without destroying fullerene molecule.” Where became it appropriate to investigate properties of endohedral metallofullerenes””by doped with various number of atoms” In the present work we have investigated the stability of structures, binding energies per atom and vertical ionize potential and energy gap of Ru and Pd doped C60 fullerene by optimizing the atomic geometries.

COMPUTATIONAL DETAILS This is the first paragraph – text set with no indent but justified””This is our preferred style for all first paragraphs after headings““We performed ab initio calculations by using an efficient computer code““known as SIESTA [15, 16] which is based on the standard Kohn–Sham self-consistent density functional theory (DFT) The pseudopotentials is constructed using a Trouiller–Martins scheme [9, 16] to describe the interaction of valence electrons with the atomic cores““The exchange-correlation potential of Perdew–Burkle–Ernzerhof (PBE) for generalized gradient approximation (GGA) corrections are adopted [17]””The atomic orbital set employed throughout was a double- plus-zeta polarization DZP function [18]””For the calculations of cohesive energies““we considered that the ground states of an isolated carbon atom and silicon atom are in the triplet states““We have performed tests calculations on C60 and Ru2 molecule““we found the bond length of C-C to be 1.41 Aº and 1.46 Aº in agreement with experimental values (1.4 Aº 0.01 and 1.46 Aº) [19]””for double and single bonds respectively””The values of ionization potential and the electron affinity are (7.099 eV and 2.326 eV)““these values are in agreement with the experimental values (7.5 0.01 eV and 2.689 0.008 eV) respectively “”For the Ru2 molecule the Ru-Ru bond length is 2.743 Aº agrees well with the experimental values 2.79 Aº [20-23]. We have successfully described the structural and electronic properties of Ru and Pd doped fullerenes””which validates the applicability of our calculation on carbon, Ru and Pd based system””The binding energy of the complexes is calculated from the energy difference between the reactants (C atom and the relevant number of Ru and Pd atoms) and the complex product species””The binding energy is calculated using”

ǤǤൌሺ̷͸ͲȂ͸ͲȂሻȀ

(1)

Where B.E. is the binding energy per atom of Ru and Pd endohedral metallofullerenes C60”M is the materials dopant””EMn@C60 the total energy of the C60 with n is material atoms encapsulated inside C60”EC60 is the total energy of pure C60. The EMn is the total energy of one materials atoms, and n is the number of materials dopant atoms “”The optimized C60 cage structure was used for materials are interactive””We assign initial coordinates to material atoms and carbon atoms of C60 molecule and allow the system to relax with respect to all degrees of freedom without additional constraints. The structures investigated include dopant atoms varying from 1-4.

RESULTS AND DISCUSSION We calculated in this present work binding energy per/ atom ionization potential Fermi levels and energy gap for endohedral metallofullerenes varies with the number of Ru and Pd atoms.”The optimized structures are presented in figure 1. The Ru and Pd small clusters endohedral metallofullerenes C60”the number of materials dopant we put inside fullerenes up to n=4.

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Ru1@C60

Ru2@C60

Ru3@C60

Ru4@C60

Pd1@C60

Pd2@C60

Pd3@C60

Pd4@C60

FIGURE 1. Optimized structures of Run@C60 and Pdn@C60 (n=1-4).

Initially, the endohedral metallofullerenes Run@C60 and Pdn@C60 complexes (n = 1- 4) have negative binding energy and they are thermodynamically stable, the binding energy of Run@C60 has increased with the number of the Ru atoms and reaches to a maximum of 3 atoms and then decreases with increasing number of dopants to 4 atoms of Ru. While the binding energy decreases with a number of the Pd atoms in case 3atoms inside the cage the minimum values for binding energy and then increase with increasing number of dopants in 4 atoms of Pd. We observed from this calculating, the values of the binding energy of Pdn@C60 are higher the values in Run@C60, this is due to electronic correlations in orbital 4d for both dopants, show that in figure 2. In generally the total energy of the both complexes are negative, which refer to they exist in the metastable state and they are more difficult to synthesize.

Binding Energy (eV/atom)

-1.0

Run Pdn

-1.2 -1.4 -1.6 -1.8 -2.0 -2.2 -2.4

1.0

1.5

2.0

2.5

3.0

3.5

4.0

The number of Ru and Pd atoms

FIGURE 2. Variation of binding energy per atom with n (n=1-4).

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FIGURE 3. Variation of ionization potential per atom with n (n=1-4).

The ionization potential is a measure of the strength of correlation of electrons” in both Ru and Pd endohedral metallofullerenes C60, the minimum value of the ionization potential we found at n=2, because in this case increase distance between electron and nuclear of the atoms due to the impact Van der Waals force for cage. In general the ionization potential changes in on doping show that the electronic properties of C60 are in effect modified and endohedral doping makes C60 more reactive. We also refer to the figure 4”which disparities the magnetic momentum variation as a function of the number of doping Ru and Pd atoms inside the C60”Majority of substances shows magnetic nature.”These are either paramagnetic or diamagnetic.”A diamagnetic substance is one which is repelled by a magnetic field while diamagnetic behaviour is due to the presence of paired electrons in the atomic orbitals.”The fullerenes has very little role to play as far as magnetical alignments in the enclosed clusters are concerned. Mulliken charge analysis also shows that one electron is transferred from the Ru and Pd clusters to the C60 cage for n=1-4 and for n = 3-4 respectively. The existence of magnetic in Run@C60 and Pdn@C60 is quite fascinating and a new result indeed. However, there have been few reports of the magnetic moment in Ru and Pd substituted C60 molecule[16-19].

FIGURE 4. Variation of magnetic moment per atom with n (n=1-4).

We can be refer to the kinetic stability of complexes, through calculation the gap between HOMO and LUMO energy levels. Whereas, due the interaction energy for Ru and Pd endohedral metallofullerenes C60, observed changes in the energy gap. The energy gap of peor fullerenes C60 is 1.60491 eV[23], while it’s greatly modified and decreases with doping. The change in the interaction energy during deformation confirms that the decrease in the energy gap in Run@C60 and Pdn@C60 is due to the enhanced interaction between C60 and (Ru & Pd) small clusters. The distance

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between carbon and dopant atoms in Run@C60 and Pdn@C60 are obtained to support the increased interaction between them. As the compressive force increases, carbon atoms come closer to the water molecule. The energy gap varies with the number of Ru and pd atoms inside Fullerene are represented in table (1), shows the energy gap increasing upto n=3 with increase the number of dopants. TABLE 1. Represented the energy gap for compounds Run@C60 and Pdn@C60. Energy Gap (eV) No.atoms Pdn@C60

Run@C60

0.202 0.965 0.893 0.803

0.457 0.688 0.696 0.524

1 2 3 4

CONCLUSION Through help of density functional theory to investigate the properties of endohedral metallofullerenes. Calculations was conducted to study some effects of Ru and Pd doping in C60. Geometry parameters indicated that the C-C distances are enlarged as a result of doping””The characteristic bands of C60 are shifted slightly toward semiconductor””The charge is increased as a result of Ru and Pd doping””Finally, We conclude that Fullerene can accommodate atoms 4 Ru or Pd atoms inside C60 without distorting. Observed from this calculating, the values of the binding energy of Pdn@C60are higher the values in Run@C60, this is due to electronic correlations in orbital 4d for both dapots, and the ionize potential we found in both Ru and Pd encapsulate fullerenes C60, the minimum value of the ionization potential we found at n=2, because in this case increase distance between electron and nuclear of the atoms due to the impact Van der Waals force for cage, Is due to increase distance between electron and nuclear of the atoms. The presence of magnetic moment in Run@C60 and Pdn@C60 is quite fascinating and a new result indeed.

ACKNOWLEDGMENTS Authors are thankful to the SIESTA group for providing their computational code, greatly acknowledge for Department of Physics, Faculty of Science, Karbala University, Karbala, Iraq, and Department of Physics, Panjab University, Chandigarh, India.

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