Computational Materials Science from an ab-initio point of view is mostly based on density functional theory (DFT) which is also the first rung on the multi-scale modelling ladder to quantitatively describe processes and phenomena seen in real materials. It has proven to be an excellent technique for the calculation of structures and molecular dynamics, and therefore a variety of popular DFT codes have already been established for being used by a large and even swiftly growing community.

While most of the applications are still dedicated to investigate ground-state properties, there is rapidly increasing demand in understanding and predicting various kinds of excitations. The topics range from light-matter interaction, spin fluctuations and lattice vibrations to situations where several fundamental excitations take place on the same energy scale and thus interact with each other. Hence, we enjoy exploring exciting basic scientific questions which, at the same time, are important in terms of industrial applications. While light- or current-induced electronic excitations play the major role in opto-electronic devices, lattice excitations and their interaction with the electronic system give rise to phenomena like superconductivity or the thermal behavior of materials. Solar cells and light-emitting diodes are of greatest industrial relevance today as much as high-strength materials or thermal coatings. Such scenarios ask for the development of basic concepts as well as the corresponding computer codes to be capable of dealing with these situations. The CECAM workshop aims at providing training to young people in this respect, making them familiar with the EXC!TiNG code, a package which is dedicated to excited state properties.
 

The exciting code

EXC!TiNG is a young public-domain all-electron package based on DFT for the investigation of condensed matter on the atomic scale. It combines several major advantages:
- It is a full-potential all-electron code based on the LAPW method, which stands for highest precision and the fact that it can be used for any material.
- It is the only all-electron package comprising vast implementations of excited state properties within TDDFT as well as MBPT.
- It is developer-friendly through a clean and fully documented programming style,  a modern source-code management, a dynamical build system, and automated tests.
- It is user-friendly through an easy-to-handle user interface comprising various tools to create and validate input files and analyze results.
- It is seminal by being interfaced to packages operating on the next higher length scale and by the development of tools which allow for the handling by users from an industrial environment.