B4 Research Projects 2023
(Krüger)
Project 1: ARPES intensity calculation of organic semiconductors
Background. Electron and hole carrier transport in organic semiconductors is a key issue for applications such as OLEDs and photovoltaics. Angle-resolved photoemission (direct or inverse) is one of the most important experimental techniques to probe the electronic states involved in the transport, especially the HOMO and LUMO bands. It is well known that the ARPES intensity dis- tribution gives detailed information about the wave function character of the probed states [1] this information is most often disregarded and the ARPES analysis is focused exclusively on the peak energies, i.e. the band dispersion. Despite extensive research, even relatively simple organic semiconductors with good crystallinity, such as rubrene and pentacene, the ARPES data of HOMO and LUMO bands is still not well understood [2-5].In this project, we develop a simple theory of ARPES for organic semi- conductors, based on the on-step model of photoemission, plane-wave ap- proximation for the final state, and a tight-binding model for the HOMO or LUMO bands.
Tasks
1. DFT calculation of HOMO or LUMO molecular orbital ψ(r) of the free molecule but in the conformation as found in the solid
2. Momentum represention of the wave function ψ̃(p) by Fourier trans- form
3. Construction of a tight-binding (TB) model (from literature data or DFT+Wannierization) of the relevant band.
4. Diagonalization of the TB model
5. Implementation of the theory below for computing the ARPES spectra
6. Comparison with experimentat data [2-5].
7. Future extension: effect of vibration-induced disorder
[1] P. Puschnig et al. Reconstruction of Molecular Orbital Densities from Photoemission Data, Science 326, 702 (2009). DOI: 10.1126/science.1176105
[2] Y. Nakayama et al. Single-crystal pentacene valence-band dispersion and its temperature dependence. J. Phys. Chem. Lett. 8, 1259 (2017). DOI: 10.1021/acs.jpclett.7b00082
[3] J. Nitta et al. The actual electronic band structure of a rubrene single crystal. Sci Rep 9, 9645 (2019). DOI: 10.1038/s41598-019-46080-4 Rep 2019
[4] 佐藤 晴輝, 学位論文, 千葉大学 (2023).
[5] H. Sato et al. Conduction band structure of high-mobility organic semiconductors and partially dressed polaron formation, Nature Mat. 21, 910 (2022). DOI: 10.1038/s41563-022-01308-z
[6] 山本蒼波氏,修論,千葉大3/2022.
Project 2: ARPES of Ni-doped magnetite Fe3O4.
Background. Magnetite (Fe3O4) is an important material for magnetism and catalysis. The surface electronic structure of Ni-doped has recently been measured with angle-resolved photoemission (ARPES) [1]. Krüger has calculated the ARPES patterns using multiple-scattering calculations and good agreement with experiment was obtained. However, the crystal potential was generated from bulk Fe3O4. In this project a better potential, which includes surface effects, will be computed using density functional theory (VASP) code and the ES2MS package [2,3] which allows to generate multiple-scattering potential from charge densities of plane-wave codes (such as VASP).Tasks
1. Run DFT VASP calculation for the Fe3O4 surface and Ni:Fe3O4.
2. Install the ES2MS code [2] and use it to generate the atomic potentials.
3. Compute ARPES patterns using the real-space multiple scattering method [4].
[1] M. Taskin, P. Krüger et al. Surface Electronic Structure of Ni-doped Fe3O4(001) Surfaces (preprint).
[2] J. Xu et al. ES2MS: An interface package for passing self-consistent charge density and potential from Electronic Structure codes To Multiple Scattering codes. Computer Physics Comm.203, 331 (2016). DOI: 10.1016/j.cpc.2016.02.031
[3] J. Xu, P. Krüger et al. X-ray absorption spectra of graphene and graphene oxide by full-potential multiple scattering calculations with self-consistent charge density, Phys. Rev. B 92, 125408 (2015) DOI: 10.1103/PhysRevB.92.125408.
[4] P. Krüger et al. Real-space multiple scattering method for angle-resolved photoemission and valence-band photoelectron diffraction and its application to Cu(111), Phys. Rev. B 83, 115437 (2011). DOI: 10.1103/PhysRevB.83.115437
Project 3: Theory of resonant photoemission of Ni-doped SrTiO3
Strontium titanite is a material with many applications. Ni-doping improves its optical properties in view of photovoltaic applications. Recently, the electronic structure of Ni:SrTiO3 has been investigated with normal and resonant photoemission (resPES) [1]. ResPES gives information about the local electronic structure around a selected element and crystal site. No resPES calculations have yet been performed. The aim of this project is compute resPES spectra in a cluster model.Tasks
1. Run DFT VASP calculation for the Ni:SrTiO3. Analyze the density of states and wave functions.
2. Learn about resPES [2,3].
3. Make a simple, nearest neighbor cluster model for resPES.
4. Write a program that diagonalizes the hamiltonian and computes the resPES spectra.
[1] F. Alarab et al. Photoemission study of pristine and Ni-doped SrTiO3 thin films, Physical Review B 104, 165129 (2021). DOI: 10.1103/PhysRevB.104.165129
[2] R. Sagehashi, G. Park, P. Krüger, Theory of circular dichroism in angle-resolved resonant photoemission from magnetic surfaces, Phys. Rev. B 107, 075407 (2023) DOI: 10.1103/PhysRevB.107.075407
[3] F. Da Pieve, P. Krüger, Real-space Green's function approach to angle-resolved resonant photoemission: Spin polarization and circular dichroism in itinerant magnets Phys. Rev. B 88, 115121 (2013). DOI: 10.1103/PhysRevB.88.115121
Project 4: Shape of manganese oxide nanocrystals
Manganese oxide (MnOx) exists in many oxidation states (MnO,Mn3O4,Mn2O3,MnO2). MnOx nanocrystals of a few nm size are promising for catalysis. Structural analysis of such small particles is difficult since X-ray diffraction cannot be performed. The aim of this project is to study the stable shapes Mn2O3 nanoparticles and their possible surface terminations.Tasks
1. Learn to use the molecular dyanmics program LAMMPS [1]
2. Choose an inter-atomic potential (e.g. Born-Mayer) and fit its parameters to the bulk properties of Mn2O3.
3. For a given particle size, construct various cluster shapes, optimize the structure using LAMMPS and find the most stable ones.
[1] https://www.lammps.org
Project 5: Adsorption of flourine on the gold Au(111) surface
The understanding for the flourine-metal interface is a key element in the development of flourine ion shuttle batteries [1]. Recent (unpublished) experiments of F adsorbed on Au(111) indicate very different structures as compared to F/Cu(111) [2] and also to Cl/Au(111) [3]. The aim of this project is to study the adsorption of F on Au(111) using density functional theory calculations.Tasks
1. Make a model of the Au(111) surface and calculate is with DFT-VASP.
2. Calculate adsorption energies of F/Au(111) and the structure of a F atomic layer, as a function of the amount of adsorbed F.
3. Compute the energy for diffusion of F into Au(111).
[1] H. Nakano et al. Fluoride-Ion Shuttle Battery with High Volumetric Energy Density Chem. Mater. 33, 459 (2021) DOI: 10.1021/acs.chemmater.0c04570
[2] M. N. Petukhov, P. Krüger et al. 2D Missing Row Structure of Cuprous Fluoride on Cu(001) J. Phys. Chem. C 126, 21390 (2022). DOI: 10.1021/acs.jpcc.2c06295
[3] S. Peljhan and A. Kokalj, Adsorption of Chlorine on Cu(111): A Density-Functional Theory Study, J. Phys. Chem. C 113, 14363 (2009) DOI: 10.1021/jp902273k
Project 6: Calculation of photoluminescence spectra of praseodymium Pr3+ ion in solid laser materials
Praseodymium (Pr3+) compounds are widely used for solid state lasers. Understanding the photoluminescence spectra is important for finding the best host material of the Pr3+ ion for efficient laser performance. The aim of this project is to compute the photoluminescence using the model and program that has been developed in the research group and improve the theory/model/program if necessary.Tasks
1. Compute crystal field of Pr3+:LiYF4 in point ion model
2. Compute single ion Pr3+ interaction parameters
3. Compute photoluminiscence spetrum and compare with experiment and previous theory [1]
[1] L. Esterowitz et al. Energy levels and line intensities of Pr3+ in LiYF4, Phys. Rev. B 19, 6442 (1979). DOI: 10.1103/PhysRevB.19.6442
Project 7: Mn/Fe(110) thin film structure and magnetism
Antiferromagnetic materials are considered for information storage and antiferromagnetic films on ferromagnets can be used as spin-valve systems. The Mn/Fe(100) interface has been studied well in the past. Surprisingly, little is know about Mn/Fe(110), although the (110) face is the most stable surface in a bcc crystal. Recently Prof 山田豊和's group has grown thin layers of Mn on Fe(110) (which is the most stable of the bcc surfaces) and observed it by STM. The periodicity is complex (at least a 2x3 supercell) and the the contrast changes in STM may be due to corrugation (structure) or a complex magnetic state. The aim of this project is to compute the stable structure of 1 ML Mn on Fe(110) and analyze the electronic and magnetic state and the STM images.[1] Y. Kosuge and T. K. Yamada, DOI:10.1380/vss.63.459
[2] 松原颯汰卒論要旨,
[3] 松原颯汰卒論スライド,
Project 8: Contribution to ARPES theory development
Several possibilities:- improve Krüger's multiple scattering code by using full potential T-matrices (to be calculated by code developed by 藤方悠さん.
- generalize t-matrix calculation (muffin-tin) to complex energies ...