Investigation of conducting polymers by computer simulations Regina Burganova Supervisor: Tayurskii D.A. Erokhin V.V. Scientific consultant: Lysogorskii Y.V. Can plastics conduct? Alan J. Heeger, Alan G. MacDiarmid and Hideki Shirakawa made a breakthrough in 1977 Nobel Prize in Chemistry in 2000 for the discovery and development of electronically conductive polymers Conjugated polymers Different class of materials: -conjugated systems Alternate single-double bonds Exhibit the electrical and optical properties of metals or semiconductors upon doping Doping of conjugated polymers Practical application Solar cells Biosensors Color displays Organic memristor Why polymers? Low cost Easy synthesis/processability Transparent Mechanical properties *V.Erokhin, "Organic memristors: Basic principles." In Circuits and Systems (ISCAS), 5-8. (2010). [*] Polyaniline General structural formula: Environmental stability Controllable electrical conductivity Interesting redox properties High conductivity in doped state A-B type of polymer First proton doped polymer the most stable in air! Polyaniline doping ACID-BASE CHEMISTRY (proton doping) REDOX CHEMISTRY (charge transfer) Emeraldine base Leucoemeraldine base Conductivity ~ Sm/cm Conductivity ~ 400 Sm/cm Emeraldine salt Band structure of doped polyaniline 0.65 eV Stafstrm, S., et al. "Polaron lattice in highly conducting polyaniline: theoretical and optical studies." Physical Review Letters (1987): 1464. EPR signal Epstein, A. J., et al. "Insulator-to-metal transition in polyaniline." Synthetic Metals 18.1 (1987): Protonation mechanism Two-step transition from isolated, doubly charged, spinless bipolarons to a polaronic metal: (i) Instability of a bipolaron on a chain (ii) formation of two polarons (iii) separation of polarons, polaronic lattice Is polaron lattice energetically favorable? MacDiarmid, A. G., et al. "Polyaniline: a new concept in conducting polymers."Synthetic Metals 18.1 (1987): Emeraldine base Bipolaron lattice Polaron lattice Goal To investigate polyaniline by means of ab- initio methods: Geometric structure; Electronic structure; Vibrational properties. DFT vs DFTB High accuracy Restricted computational efficiency High computational efficiency Kohn, W., & Sham, L. J. (1965), Physical review, 140(4A), A1133. Elstner, M., Porezag, D., Jungnickel, G., Elsner, J., Haugk, M., Frauenheim (1998), Physical Review B, 58(11), 7260. Simulation details DFT: VASP (MedeA env.), GGA-PBE functional; DFTB: DFTB+ with Slater-Koster parameters (3ob-3-1 set); c G (0,0,0)B (0.5,0,0) Emeraldine base infinite chain c=20.2 A Band structure/Density of States/Charge distribution HOMO LUMO 0.90 eV 2.93 eV *Huang, W. S., and A. G. MacDiarmid. "Optical properties of polyaniline." Polymer 34.9 (1993): [*] G (0,0,0)B (0.5,0,0) Polaron lattice Bipolaron lattice c ~ 20.6 A E P-B = 2.1 meV Emeraldine salt: Polaron vs Bipolaron lattice Bond lengths Band structure/Density of States/Charge distribution G (0,0,0)B (0.5,0,0) Bipolaron lattice Polaron lattice HOMO LUMO HOMO LUMO Crystalline structure of polyaniline I class: ES-I -> EB-I (amorphous) II class: EB-I -> ES-II -> -> ES-II (50% crystalline) Realistic 3D polymer model Pouget, J. P., et al. "X-ray structure of polyaniline." Macromolecules 24.3 (1991): ES-II ES-I EB-II Nonshifted chains a = 5.75 A* b = 7.80 A* c = 20.2 A Shifted chains 3D Emeraldine base *Pouget, J. P., et al. "X-ray structure of polyaniline." Macromolecules 24.3 (1991): a = 7.90 A* c = 20.6 A b = 7.10 A* Nonshifted chains Shifted chains *Pouget, J. P., et al. "X-ray structure of polyaniline." Macromolecules 24.3 (1991): D Emeraldine salt: Polaronic lattice a= 7.90 A* c = 20.6 A b = 7.10 A* Nonshifted chainsShifted chains 3D Emeraldine salt: Bipolaronic lattice *Pouget, J. P., et al. "X-ray structure of polyaniline." Macromolecules 24.3 (1991): Emeraldine base Polaron lattice Bipolaron lattice 3D polyaniline energy Vibrational properties: Emeraldine base Scaling factor = *Berzina, T., Erokhin, V., & Fontana, M. P. (2007). Journal of applied physics, 101(2), Vibrational properties: Emeraldine salt Scaling factor = *Berzina, T., Erokhin, V., & Fontana, M. P. (2007). Journal of applied physics, 101(2), Vibrational properties: Emeraldine salt Scaling factor = *Berzina, T., Erokhin, V., & Fontana, M. P. (2007). Journal of applied physics, 101(2), IR spectrum assignments IR assignment f, cm-1 theory f, cm-1 calculationIR assignmentf, cm-1 theoryf, cm-1 calculation Aromatic ring deformation628, ,200406C-N stretching in QBQ1379, , C-H out-of-plain bending of 1,4 ring826, ,140354Stretching of N-B-N1502, , C-H out-of-plain bending of 1,2,4 ring953, , Stretching of N=Q=N1596, ,11376 C-H in-plain bending of 1,2,4 ring1103, ,266024H-bonded NH stretching2880, ,5 C-N stretching in BBB1252, ,443302H-bonded NH stretching3337,083180,83 C-N stretching in QBQ, QBB, BBQ1298, , IR assignmentf, cm-1 theory f, cm-1 calculationIR assignmentf, cm-1 theoryf, cm-1 calculation Aromatic ring deformation616, , C-N stretching in QBQ1496, , C-H out-of-plain bending of 1,4 ring820, ,429025Stretching of N-B-N1573, , C-H out-of-plain bending of 1,2,4 ring881, , Stretching of N=Q=N2361,4077 C-H in-plain bending of 1,2,4 ring1152,259991, H-bonded NH stretching2925,772891,67 C-N stretching in BBB1246, ,202858H-bonded NH stretching3224,523196,38 C-N stretching in QBQ, QBB, BBQ1301, , PANI blue PANI green Conclusions and future work DFTB gives good description of geometry and electronic properties; The calculations shows polaronic lattice is energetically more favorable than bipolaronic one; 3D PANI structures need additional investigation; Experimental PANI IR spectra assignments present in the calculated spectra, but have frequency shifts IR spectra need to be improved. Simulation of Li + ion diffusion in polymers Organic memristor Working principle: *V.Erokhin, "Organic memristors: Basic principles." In Circuits and Systems (ISCAS), 5-8. (2010). LiClO 4 salt model Amorphous builder H 2 O /LiClO4 T=300K, Nmol=600/c LAMMPS: minimization LAMMPS: NPT dynamics for 100ps, T=300K, p=1atm Remove water FF: pcff+ initialization Molecular builder MedeA PEO model FF: pcff+ initialization LAMMPS: minimization LAMMPS: NPT dynamics for 100ps, T=300K, p=1atm Polymer builder LAMMPS: NVT dynamics for 100ps, T=300K, p=1atm Molecular builder MedeA Amorphous builder T=300K, ro=1.21 mg/m 3 Li + diffusion in solid electrolyte model Merge LiClO 4 LAMMPS: minimization LAMMPS: NPT dynamics for 100ps, T=300K, p=1atm Diffusion: NVE dynamics for 200ps D: MSD evaluation Preliminary results Exp GF NMR: D=4.323*10 -9 cm 2 /s Future work Verification of results; Temperature dependence; Li + diffusion in PANI, PEO-PANI heterostructure; Diffusion in electric field; Measurements.