With more than 1250 registered users, ABINIT [1-3] is nowadays a well-established open software package for the first-principles calculations of the properties of solids (more than 2200 cites of ABINIT papers on Web of Knowledge (Thomson)). One of the strengths of the package is the straightforward computation and easy analysis of various physical quantities using the linear and non-linear responses formalism (phonons, interatomic force-constants, electron-phonon coupling, dielectric constant, Born effective charges, Raman tensor, elastic constants, piezoelectric constants, non-linear optical susceptibilities, electro-optic coefficients, thermodynamic properties) [4-10]. In addition, other “advanced” properties can be computed using ABINIT, such as quasi-particle energies in the GW approximation, or optical properties with the Bethe-Salpeter equation. Extensive on-line tutorials and an active forum already provide a helpful basic support to users. However, regular and recurrent questions on the forum highlight the limitation of such on-line tools and the need for additional concrete training in direct contact with ABINIT developers.
Four ABINIT tutorials on linear and non-linear responses have been organized to date, in Santa Barbara, USA (2005), in Queretarro, Mexico (2008), CECAM, Lausanne (2010), and CECAM, Zurich (2012). Our evaluations indicated that they were all successful, and impacted a large number of users (around 60, 50, 30, 30 and 40 respectively – set by space limitations). The tutorial courses provide a unique opportunity for users to build a solid and structured background on how physical quantities are practically computed within the code, in a more pedagogical setting, and with more practical details than in the literature. In addition, more complex examples are given than those found in the basic on-line tutorials, and the interaction with experts helps new users fine-tune parameters to deal properly with the calculations on a case-to-case basis. Finally, the tutorial courses strengthen links within the ABINIT community, and motivate the next generation of developers within the user population, so ensuring the continuity of the project. For all these reasons, the ABINIT developers are strongly motivated to organize ABINIT tutorials on a regular basis. In view of the success of the last tutorial in Zurich, and the fact that our user base is concentrated in Europe, we feel that it would be particularly relevant at this stage to organize a new tutorial in Europe, especially in the context of CECAM.
Complementarily to other similar schools in the field that mainly focus on the basics of electronic structure calculations, our proposed tutorial intends to present more advanced features of the ABINIT package. In particular, in this tutorial course we propose to cover responses with respect to strain, the computation of Raman tensors, and the PAW treatment of the response to electric and magnetic fields. The proposed tutorial is addressed mainly to the community of young European students and postdocs interested in the fields of vibrational spectroscopies, thermodynamics, thermal properties, non-linear dynamical properties, etc. Applications will concern a wide variety of materials such as semiconductors, ferroelectrics, piezoelectrics and multiferroics, insulators, crystalline and disordered materials, nanostructures, Earth and planetary materials, etc.
This proposed ABINIT tutorial course will include two types of activities : (1) lectures on theory, algorithms and implementations in the morning sessions and (2) hands-on exercises in the afternoon sessions. The lectures and exercises will be synchronized in such a way as to have the practical applications of the morning classes investigated in detail with the developers’ support in the afternoons. A poster session is planned with posters displayed at least for the second half of the tutorial week.
The tutorial will cover in five days the following topics:
- density functional theory (DFT) and density functional perturbation theory (DFPT) in both the standard planewave-pseudopotential and projector-planar augmented wavefunctions (PAW) formulations,
- phonon band structures, thermodynamical properties, and isotope partitioning
- response functions and couplings with electric fields
- response functions and couplings with strain
- response functions and couplings with magnetic field; magnetic properties and magnetic transitions; Moessbauer spectra
- response in finite electric field
- Raman and electro-optic responses
- electron-phonon coupling
Each morning lecture will consist in a 2 hour presentation including a 10-15 minutes break. The afternoon hands-on exercises will be based on the on-line ABINIT tutorials and supervised by the morning teachers.
From our previous experience, this type of tutorial typically attracts two kinds of students: some advanced students who already know the basic of DFT and want to learn about linear and non-linear responses and some beginner students who need to acquire some basic background about DFT before going further in the response formalism. To make the tutorial attractive and highly beneficial to all students, we propose to deal with 2 groups in parallel during the first two days, giving a lectures on the PAW implementation to advanced students during the time beginners learn the basics of DFT and its implementation in ABINIT. Then, from the middle of the second day all students will follow the same lectures as detailed in the plan below.
We already applied this format during the previous tutorials at CECAM in 2010 and in 2012 and it was a great success. In order to better take advantage of the combination of beginners and more advanced students, the advanced students will act as tutors for beginners during the hands-on sessions, complementarily to the support by lecturers. This was already informally happening in previous schools and found beneficial by all types of students.
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