tool for characterisation and prediction in materials science. There is an expanding literature on solar energy (e.g. active layers, interfaces, transparent conducting oxides). Aim: A basic understanding of terms and concepts, with the ability to critically assess results from research papers in your field.
the Schrödinger equation and chemical composition as the sole input Why? Accurate, unbiased, and predictive When? If such calculations are feasible and meaningful How? Digital computers, clever algorithms, common sense, and scientific rigor Source: http://stefano.baroni.me/presentations/
Operators ˆ H = ˆ T + ˆ V Non Relativistic Relativistic Schrödinger (1887, Vienna) Dirac (1902, Bristol) Extra terms: scalar relativistic spin-orbit coupling
Wavefunction based quantum mechanics Methods Hartree-Fock Møller–Plesset Configuration Interaction Methods Thomas–Fermi Density Functional Dynamical Mean Field
Total Energy + Electronic Structure Structure atomic forces equilibrium coordinates atomic vibrations phonons elastic constants Thermodynamics internal energy (U) enthalpy (H) free energy (G) activation energies (ΔE) Electron Energies density of states band structure effective mass tensors electron distribution magnetism Excitations transition intensities absorption spectra dielectric functions spectroscopy
Periodic cell potential Plane waves 4.3. DENSITY-FUNCTIONAL THEORY: IMPLEMENTATION 55 Bloch waves describe local (intra unit cell) and long-range (inter unit cell) interactions in a crystal
Austria (Prof. Georg Kresse) • License fee ~€5000 (small academic group) • Site: http://www.vasp.at • Forum: http://cms.mpi.univie.ac.at/vasp-forum • Wiki: http://cms.mpi.univie.ac.at/wiki • Many pre- and post-processing tools • Visualisation: http://jp-minerals.org/vesta A popular package because of reliable pseudopotentials for periodic table (benchmarked against all-electron methods)
Card”) • INCAR (“Input Card”) • KPOINTS (k-point Sampling) All four files should be in the same directory for VASP to run successfully Caution: The order of the elements in POTCAR must be the same as POSCAR
[Positions] Card”) • CHGCAR (“Charge Density Card”) • vasprun.xml (Auxiliary output as xml) A number of additional files that are generated depending on flags set in INCAR Caution: If NSW > 0, a number of the properties are averaged over past structures (rerun with NSW=0 at end)
2011) Electronic band gap ≠ Optical band gap N-1 quasi-particle N+1 quasi-particle (electron + interaction with environment) N excitation (e-h interaction)
in CuGaS2 ? 1. Log on to: https://materialsproject.org 2. Download the most stable crystal structure of CuGaS2 3. Open in VESTA (http://jp-minerals.org/vesta/en/) and draw bonds [EDIT: BONDS]
Holes Effective semiconductors Lattice Vibrations Symmetry breaking and carrier separation Molecular Rotations Large static dielectric constant Ions and Charged Defects “Self healing” and hysteresis J. M. Frost and A. Walsh, Acc. Chem. Res. 49, 528 (2016)
et al, JPCL (2014); Unger et al, EES (2014)] • Rapid chemical conversion between halides [Pellet et al, CM (2015); Eperon et al, MH (2015)] • Photoinduced phase separation [Hoke et al, CS (2015); Yoon et al, ACS-EL (2016)] • Electric field induced phase separation [Xiao et al, NatM (2015); Yuan et al, AEM (2016)]
slow exchange to the bulk crystal Frost, Whalley, Walsh, ACS Energy Letters 2, 2647 (2017) Low Density n < 1018 cm-3 High Density n > 1018 cm-3 (Laser source) Notebooks: https://github.com/WMD- group/hot-carrier-cooling
time scales • First-principles techniques can accurately predict structure and properties • Materials data and reproducibility is becoming increasingly important Slides: https://speakerdeck.com/aronwalsh news & views e spoiled for urally occurring iodic table give y compounds ry compounds ompounds, each element inations exceed nent system. the number of ALS uest for new functionality tanding of the chemical bond, advances in synthetic chemistry, and large-scale computation, ow become a reality. From a pool of 400 unknown compositions, 15 new compounds have pt the expected structures and properties. Structural prediction Property simulation Targeted synthesis Chemical input Figure 1 | A modular materials design procedure, where an initial selection of chemical elements is subject to a series of optimization and screening steps. Each step may involve prediction of the crystal Future:
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