The basic theory that describes the chemical bond - and practically all observable phenomena around us - is quantum mechanics. What is appealing about quantum mechanics is that this theory is truly free of any materials-specific parameter. It provides a mathematical recipe that is, in principle, capable of predicting the properties of any material by purely computational means. Ideally, the basic properties that are determined at the atomic scale can then enter larger-scale, phenomenological but validated models. Examples include materials parameters of simple metallic solids such as elasticity, thermal expansion, etc., electronic properties of semiconductor nanostructures, their optical properties, etc.
The primary workhorse theory of the field today is density functional theory (DFT), often used at the level of so-called "semilocal" or (more expensive) hybrid functionals. Beyond that, many-body approaches can give a more accurate description of ground- and excited state properties of "difficult" materials. The quantum nature of nuclei is most often incorporated by the so-called "Born-Oppenheimer" approximation - treat the electrons first, and then use the result to look at the "motion" (vibrations, phonons, ab initio molecular dynamics, statistical mechanics) of the nuclei. In practice, this usually works very well - where it does not, schemes to incorporate electron-nuclear coupling beyond "Born-Oppenheimer" for "real" (large and complex) systems are an active frontier of the field.
All these aspects are what we pursue in the context of the "FHI-aims" all-electron electronic structure package. This is a general-purpose electronic structure code for a wide range of applications. For DFT (semilocal and hybrid functionals) the code treats molecules (non-periodic) and periodically repeated geometries (solids, surfaces, nanostructures, models of liquids, ...) on exactly equal footing. Among its distinguishing factors are our focus on making accurate numerical results affordable even for rather large systems (thousands of atoms) and work on parallel scalability, allowing us to use supercomputers with perhaps (ten)thousands of CPU cores effectively. Arguably the key (most widely cited) publications behind the code are:
- Volker Blum, Ralf Gehrke, Felix Hanke, Paula Havu, Ville Havu, Xinguo Ren, Karsten Reuter, and Matthias Scheffler,
Ab initio molecular simulations with numeric atom-centered orbitals
Computer Physics Communications 180, 2175-2196 (2009).
- Ville Havu, Volker Blum, Paula Havu, and Matthias Scheffler,
Efficient O(N) integration for all-electron electronic structure calculation using numerically tabulated basis functions
Journal of Computational Physics 228, 8367-8379 (2009).
- Xinguo Ren, Patrick Rinke, Volker Blum, Jürgen Wieferink, Alex Tkatchenko, Andrea Sanfilippo, Karsten Reuter, and Matthias Scheffler,
Resolution-of-identity approach to Hartree-Fock, hybrid density functionals, RPA, MP2, and GW with numeric atom-centered orbital basis functions
New Journal of Physics 14, 053020 (2012).
This development happens in close collaboration with other groups in Berlin, Munich, Helsinki, London and elsewhere around the world. This work is happening at a rapid pace - see our publications page for details. Recent milestone publications include a detailed spin-orbit coupling benchmark, hybrid functional calculations for periodic solids beyond 1,000 atoms or the stress tensor for numeric atom-centered orbital density-functional theory:
- William P. Huhn, V. Blum
One-hundred-three compound band-structure benchmark of post-self-consistent spin-orbit coupling treatments in density functional theory
Physical Review Materials 1, 033803 (2017).
- Sergey Levchenko, Xinguo Ren, Jürgen Wieferink, Rainer Johanni, Patrick Rinke, Volker Blum, Matthias Scheffler
Hybrid functionals for large periodic systems in an all-electron, numeric atom-centered basis framework
Computer Physics Communications (2015), doi:10.1016/j.cpc.2015.02.021.
- Franz Knuth, Christian Carbogno, Viktor Atalla, Volker Blum and Matthias Scheffler
All-electron Formalism for Total Energy Strain Derivatives and Stress Tensor Components for Numeric Atom-Centered Orbitals
Computer Physics Communications 190, 33-50 (2015). DOI:10.1016/j.cpc.2015.01.003. Preprint download
In addition, our developments are also embedded in the broader community of electronic structure developers around the globe, aiming to solve key underlying problems in the form of shared library infrastructures - including CECAM's Electronic Structure Library and the "ELSI" infrastructure for massively parallel electronic structure theory, led by our group:
- Victor Wen-zhe Yu, Fabiano Corsetti, Alberto Garcia, William P. Huhn, Mathias Jacquelin, Weile Jia, Björn Lange, Lin Lin, Jianfeng Lu, Wenhui Mi, Ali Seifitokaldani, Alvaro Vazquez-Mayagoitia, Chao Yang, Haizhao Yang, Volker Blum
ELSI: A Unified Software Interface for Kohn-Sham Electronic Structure Solvers
Computer Physics Communications 222, 267-285 (2018), DOI: 10.1016/j.cpc.2017.09.007 .
Preprint: arXiV:1705.11191 [physics.comp-ph].