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Upma, et al., International Journal of Advanced Engineering Research and Studies

E-ISSN2249–8974

Proceedings of BITCON-2015 Innovations For National Development National Conference on : Nanostructured Materials and their Characterization

Research Paper

AB INITIO STUDIES ON ELECTRONIC STRUCTURE AND CHARGE DENSITY OF POTATO STARCH Upma, Mohan L Verma and Rachna Singh

Address for Correspondence Computational Nanoionics Research Lab, Department of Applied Physics, FET, SSGI, Shri Shankaracharya Technical Campus- Junwani Bhilai (Chhattisgarh) INDIA, 490020 ABSTRACT Starch is a carbohydrate consisting of a large number of glucose units joined by glycosidic bonds. An ab initio study based on density functional theory implemented in computational program SIESTA is the prime theme of present paper. In which LDA exchange co-relation environment is used to obtain density of states (DOS), projected/partial density of states (PDOS), charge density, electronic band structure of some potato starch. In the first step the structure of Potato starch ( PS), glutaraldehyde (GA) and crosslinked PS-GA systems are optimized for lowest energy value. On the basis of band plot and PDOS, it can be stated that the system under study is electronically insulator but charge density analysis proves it as ionic conductors. Moreover, the contributions to the top of valence band (HOMO) and bottom of conduction band(LUMO) come predominantly from O s/p, C s/p and H s states, respectively. This is a preliminary and first study to observe theoretically the effect of cross-linking of GA in PS before its further application as an electrolyte in various electrochemical devices. KEY WORDS: Charge Density; Density of states; Local Density Approximation; projected density of states.

1. INTRODUCTION 2. COMPUTATIONAL METHOD Potato starch (PS) (C6H10O5)n is a starch extracted We sketched the molecular structures of PS(C6 from potatoes. Only few experimental work reported H10O5)n, n=4, GA and crosslinked PS-GA systems [1,2,3] and theoretical analysis is almost missing on with the help of Avogadro software[6] and further such important systems. PS contains approximately optimization process is performed in four steps i) 800 ppm phosphate bound to the starch, which optimization of mesh cut-off, ii) optimization of increases the viscosity and gives the solution slightly k-points iii) optimization of lattice anionic character [1,4]. Researchers are investigating constant/simulation box size and iv) final starch compounds as prospective photonic and nanooptimization. The LDA, the exchange co-relational technology materials due to their unique electronic, functions[7] forms within density functional theory, chemical and optical properties [5]. Therefore, we incorporated in siesta program package is used[8]. thought it would be worthwhile to perform a Norm conserving psuedopotentials and double-zeta comprehensive theoretical work based on density basis sets with polarization functions used for all functional theory. In this paper, we report the results atoms in electronic structure calculations[8,9]. The of a theoretical study emphasizing to investigate the total number of C.G steps used is 600 for all. The electronic band structure, charge density, density of main modelling parameters used along-with total states and partial DOS of potato starch and related energy after final optimization are listed in Table 1. GA-crosslinked systems. Table 1 Modelling Parameters of these systems System Simulation MeshK Total Energy (eV) Used Box size Å Cutoff Grid PS 12x12x6.5 200 6x1x1 -13234.441982 GA 8x4.5x3 100 4x1x1 -1767.136425 PS+GA 13x13x6 100 8x1x1 -14071.567972 presence and absence of GA in PS. In presence of 3. RESULTS AND DISCUSSIONS GA in PS various bonds are stretched and some free 3.1 Structural Properties The optimized structure of PS, GA and cross-linked space/volume seems to be created. In this process PS+GA are shown in Figs. 1(a-c) respectively. extra ~930 eV energy is used as mentioned in Some important optimized bond lengths are shown Table-1. This supports the experimental observation in Table-2. By comparing an obvious structural of stretching of bonds [1]. change in the bond lengths can be observed in the Table2 Modelling Parameters of PS system Bonds C18-O67 C9-O46 C10-O67

Bond Length of PS Before Optimization After Optimization 4.92151 3.42505 6.91553 6.12910 4.58431 4.17952

Table2 Modelling Parameters of PS+GA system Bonds C7 – O31 C9 – O46 C6 – C75

Bond Length of PS Before Optimization After Optimization 3.89044 3.44326 8.21903 7.36580 4.06728 3.96166

Int. J. Adv. Engg. Res. Studies/IV/II/Jan.-March,2015/291-293

Upma, et al., International Journal of Advanced Engineering Research and Studies

E-ISSN2249–8974

The relaxed structures of active materials with the structural change in shown in Figure 1 (a-c).

Figure 1: Molecular Structure of (a) PS; (b) GA & (c) PS+GA 3.2 Electronic Properties The calculated energy band diagrams of all three systems are shown in Figures 2 (a-c). It is clearly seen that the direct band gap of these systems are 4.75, 3.78 and 4.3 eV respectively, which proves that these systems are electronically insulators. Whereas experimentally it has been proved as a good ionic Figure 3 (b): GA DOS conducting electrolytes system in the doping of salts in the presence of methanol solvent. The detailed DFT study of mechanism is under progress in present lab. Figures 3(a-c) and Figures 4(a-c) show the DOS and PDOS plots of respective PS, GA and crosslinked PS+GA. The highest occupied molecular orbital (HOMO) & lowest unoccupied molecular orbital (LUMO) gap in respective DOS plots are analogous to Figure 3 (c): PS+GA DOS band gap measured in energy band plots of corresponding systems. And from PDOS plots (Figures 4 (a-c)), it can be seen that the valence band is mainly composed of p orbitals of C and O. The comparative contribution of orbitals in conduction bands are also shown. Figure 4 (a): PS PDOS

Figure 2 (a): PS Bands

Figure 4 (b): GA PDOS

Figure 2 (b): GA Bands

Figure 2 (c): PS+GA Bands

Figure 3 (a): PS DOS Int. J. Adv. Engg. Res. Studies/IV/II/Jan.-March,2015/291-293

Figure 4 (c): PS+GA PDOS 3.3 Electronic Charge Density Figures 5(a-f) show charge distribution of PS, GA and PS+ GA according to their PDOS plots. Figures 5 (ab), 5(c-d) and 5 (e-f) show HOMO and LUMO plots of PS, GA and PS+GA respectively. Carbon (C) is forming bond with Oxygen (O) and Hydrogen (H). CO-H atoms are showing covalent bonds of their electronic wave-functions. The bonding shows a significant covalent character due to sharing of charge among these atoms. The highest charge density is observed around Oxygen. It is clear that O atom shows the ionic nature. The hump appears in the electronic charge density of O atom, due to the high electronegativity which attracts the C atom.

Upma, et al., International Journal of Advanced Engineering Research and Studies

E-ISSN2249–8974

The details of complete starch based electrolytes system using some alkali salts and plasticizer are under progress. This study may be a mile stone for such biomaterials as electrolyte in various electrochemical devices. REFERENCES 1.

Figure 5 (a): PS HOMO

Figure 5 (b) PS LUMO

Figure 5 (c): GA HOMO

Figure 5 (d) GA LUMO

Figure 5 (e): PS+GA HOMO

Figure 5 (f) PS+GA LUMO4. CONCLUSIONS

The analysis of structural and electronic characteristics of the potato starch (PS) in the presence and absence of GA have been reported. From its energy bands, DOS, PDOS and charge density analysis computed using SIESTA software, the role of GA in potato starch can be clearly seen. It has been shown that these systems are electronically insulators. The detail theoretical study is under progress in present lab. This is first principle study, which is preliminary only. Int. J. Adv. Engg. Res. Studies/IV/II/Jan.-March,2015/291-293

Tiwari, T., Srivastava, N. and Srivastava, P.C., (2011). Electrical Transport Study of Potato Starch-Based Electrolyte System, Ionics, 17, 353–360. 2. Schwall, Gerhard P., Safford, Richard, Westcott, Roger J., Jeffcoat, Roger, Tayal, Akash, Shi, Yong-Cheng, Gidley, Michael J. & Jobling, Stephen A (2000). Production of very-high-amylose potato starch by inhibition of SBE A and B, Nature Biotechnology, 18, 551 - 554. 3. Pathania ,Deepak, Sharma, Reena (2012). Synthesis and characterization of graft copolymers of methacrylic acid onto gelatinized potato starch using chromic acid initiator in presence of air, Advanced Materials Letters, 3(2), 136-142. 4. http://en.wikipedia.org/wiki/PotatoStarch. 5. http://en.wikipedia.org/wiki/Starch. 6. Hanwell, M. D, Curtis, D. E, Lonie, D. C, Vandermeersch, T., Zurek , E. and Hutchison, G. R, (2012). 7. Avogadro: An Advanced Semantic Chemical Editor, Visualization and A nalysis Platform, Journal of Cheminformatics, 4, 17 . 8. Perdew, J. P., Zunger, A . , (1981). Self Interaction Correction of Density Functional Approximations for Many Electron Systems, Phys. Rev B, 23, 1306404. 9. Jose, M. S., Emilio, A . , Julian, D . G . , Alberto, G . , Javier , J., Pablo, O . (2002). The Siesta M ethod for Ab Initio Order-N Materials Simulation, Journal of Physics: Condens Matter, 14, 2745. 10. Amorim, R. G, Zhong, X., Mukhopadhyay , S., Pandey R., Rocha ,A. R. and Karna , S. P., (2013). Strain and Electric Field Induced Band Gap Modulation in Nitride Nanomembranes, Journal of Physics: Condens. Matter, 25, 195801. Note: This Paper/Article is scrutinised and reviewed by Scientific Committee, BITCON-2015, BIT, Durg, CG, India