Response treatment for the dynamical properties of materials with the ABINIT package
- Razvan Caracas (Ecole Normale Supérieure-Lyon, France)
- Nicola Spaldin (Swiss Federal Institute of Technology Zurich (ETHZ), Switzerland)
- Philippe Ghosez (University of Liege, Belgium)
- Xavier Gonze (Catholic University of Louvain, Belgium)
- Susanne Blatter (Swiss Federal Institute of Technology Zurich (ETHZ), Switzerland)
Latest news : July 10. The list of accepted participants has been finalized. Registration is closed ...
With more than 1200 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 1600 cites of ABINIT papers on ISI-WEB). 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. 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 interactive formation tools and the need of additional concrete training formations in direct contact with ABINIT developers.
Three ABINIT tutorials on linear and non-linear responses have been organized to date, in Santa Barbara, USA (2005), in Queretaro, Mexico (2008), and CECAM, Lausanne (2010) Our evaluations indicated that they were all successful, and impacted a large number of users (around 60, 50 and 30 respectively – set by space limitations). The tutorial courses provide a unique opportunity for users to build a solid and structured background on the way physical quantities are practically computed within the code, in a more pedagogical way, and with more practical details than in the original publications. In addition, more complex examples are given than found in the basic on-line tutorials, and the interaction with expert 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 users, 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 Lausanne, 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 also more advanced features of the ABINIT package. In particular, in this tutorial course we propose to cover response with respect to strains, computation of Raman tensors, and (for the first time) PAW treatment of the response to electric and magnetic fields. The proposed tutorial is addresses 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 envisaged 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 (DFTP) in both the standard planewave-pseudopotential and projector-lanar augmented wavefunctions (PAW) formulations,
- phonon band structures and thermodynamical properties
- response functions and couplings with electric field
- 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 hours 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 basic of DFT and its implementation in ABINIT. Then, from the middle of the second day all students will follow the same lecture as detailed in the detailed plan below.
We already applied this format during the previous tutorial at CECAM in 2010 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 session, 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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