Yambo hands-on tutorial on electronic and optical excitations: from basic to advanced applications
- Myrta Gruning (Queen's University Belfast, United Kingdom)
- Claudio Attaccalite (Institut Neel CNRS/UJF, Grenoble, France)
- Andrea Marini (National Research Council, Rome, Italy)
- Conor Hogan (CNR-ISM, Rome and University of Rome Tor Vergata, Italy)
- Elena Cannuccia (Institut Laue Langevin, Grenoble, France)
- Davide Sangalli (CNR-ISM, Uos di Montelibretti, Italy)
- Daniele Varsano (S3, CNR Istituto di Nanoscienze, Italy)
Important info for applicants (30/01/2013):
The application deadline is March 1st, 2013. Applicants will be informed of acceptance within a week of the deadline. Please note that the school is limited to 30 places.
In the last decade ab-initio approaches have been increasingly applied to excited-state properties. This has led to several improvements of the state-of-the-art theoretical and numerical tools. Besides the popular Time-Dependent Density Functional Theory  (TD-DFT), applied especially to problems in Chemistry and Molecular Physics, Green's function approaches, namely GW and Bethe Salpeter Equation (BSE) methods , are being applied more and more frequently to excited-state properties of a wide range of systems: not only periodic crystals – the traditional field of application – but also to nanostructures, biological molecules, defects, surfaces and interfaces [2,3].
In this context, the GW and BSE methods are becoming more and more needed and required in the curriculum/portfolio of researchers in ab-initio numerical simulations in Condensed Matter Physics and Quantum Chemistry. On the other hand, these methods and their applications to real systems are very rarely included as part of Masters or Ph.D. programmes. In fact the organizers have mainly been motivated to organize this tutorial following the very positive experience that some of them had this year at a CECAM tutorial on related subjects (http://www.cecam.org/workshop-775.html) where the students showed extreme interest and enthusiasm to learn about several aspects of the subject matter, from theoretical foundations, convergence issues, to advanced applications.
The present hands-on tutorial therefore aims to provide the students with the basic aspects of DFT and TDDFT and with basic as well as more advanced aspects of the GW and BSE methods. Theoretical lectures on the foundations of the methods will be completed with technical lectures on numerical and computational aspects. A significant part of the school will be then dedicated to hands-on tutorials, where the students will be given the opportunity to carry out excited state calculations on several paradigmatic systems using the Yambo code , under the guide of the code developers who will be present as teachers at the school.
Yambo is a GPL distributed software, based on density functional and Green's function theories, for excited-state calculations in Condensed Matter Physics. Interfaced with two of the main GPL distributed DFT codes (Quantum Espresso and Abinit), Yambo counts about 200 users. The main paper of Yambo, published mid 2009 has already collected more than 70 references. Yambo is being actively developed, having not only TD-DFT, GW and BSE capabilities – as part of the GPL distribution – but also very advanced and even unique features for describing spin-polarized phenomena, surface spectroscopies and electron-phonon coupling. For the occasion of the school, these three extensions will be released under the GPL licence and will form part of the school program, giving to the attendees the chance of learning very advanced methods, and providing them with critical tools to purse their research activity.
Specifically, the spin-polarized extension makes it possible to treat materials that may possess a magnetic ground state due to the presence of electrons in the localized d and f orbitals. The interest in those materials is growing rapidly, not only because of their possible applications in the field of spin electronics , but also following the observation of new physical effects. In particular, the Magneto-Optical Kerr Effect (MOKE), is at the basis of a powerful spectroscopic technique for probing the magnetic properties of materials . The MOKE is implemented in Yambo and will be the object of one of the advanced lectures.
Within surface science, optical and electronic spectroscopies are now commonly used alongside more traditional surface-sensitive techniques such as scanning tunneling microscope and low energy electron diffraction. In particular, reflectance anisotropy spectroscopy (RAS) and high resolution electron energy loss spectroscopy (HREELS) are used to characterize surface structure  as well as complex processes like molecular adsorption, epitaxial growth and self-assembly . Nonetheless, these techniques are generally used in a phenomenological way, without a solid interpretation from first principles calculations. In this tutorial, the theoretical background and practical techniques for simulating these experiments will be described based on dedicated routines implemented into Yambo.
The electron-phonon coupling is another crucial ingredient in first-principles electronic structure that is however missing in the vast majority of calculations . Yambo has implemented the electron-phonon coupling within the Heine, Allen and Cardona [7-10] approach. As there are only very few ab-initio calculations available in literature [11-14] this part of the Yambo hands-on will provide the students with cutting-edge skills that will promote their critical understanding of the performance of any purely electronic calculation.
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