NON ADIABATIC PHONON

Non adiabatic vibrational spectra from first principles

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 Obiettivo del progetto (Objective)

'We submit to consideration of the 7th framing EU program, Marie Curie Incoming Fellowship program, a research project in the field of computational material science to explore material thermal properties of homogeneous systems. We propose this project with the idea of setting up long term collaborations between the groups in Mexico and Germany. The proposed research program is aimed to understand, to develop and to characterize systems with novel properties originating from electronic correlations and in particular of systems where the electron-phonon coupling plays an important role in its thermal response. In that respect, we expect to use and implement two different recent proposed methodologies, which allow us to explore the non adiabatic contribution and anharmonic effects to the phonon spectra. This physical phenomena has been reported to have relevance in layered materials, such as graphene, MgB2, CaC6 and in most superconductor systems. Basically we will be implementing, within the ELK code(elk.sourceforge.net), two different methodologies to characterize thermal behavior away from the adiabatic approximation (a) a self consistent phonon calculation, where the atoms within the unit cell are displaced by a Bose-Einstein factor, such that they are able to reach a new stable minima as function of temperature (b) a fist order perburbation on the changes on the stationary forces after a time dependent perburbation on the ionic displacements is imposed into the system.'

Introduzione (Teaser)

Scientists developed complex algorithms describing the quantum vibrations in superconducting materials and their relationship to voltage generation. The phenomenon has direct application to green refrigeration and power production.

Descrizione progetto (Article)

Thermoelectric materials are gaining widespread attention for their potential in green power generation, green refrigeration and efficient 'spot' cooling of electronic devices (increasing computing speed). These materials produce a voltage difference in response to a temperature difference and vice versa. Some of their novel thermal responses are due to coupling between electrons and phonons. Phonons are quanta of vibrational energy typically in a crystal lattice or a solid. Like their electromagnetic counterparts (photons), these phonons or vibrations have frequencies and wavelengths and thus generate associated spectra.

Scientists developed new mathematical descriptions of phonon behaviours with EU funding of the project 'Non adiabatic vibrational spectra from first principles' (NON ADIABATIC PHONON). In particular, they applied two recent methodologies to explore the contribution of non-adiabatic and anharmonic effects to phonon spectra in thermoelectric materials. The former refers to conditions under which heat enters or leaves the system. The latter refers to vibrations and deviations at multiples of the harmonic or natural frequency in addition to the natural frequency itself.

The team developed a computer interface to a self-consistent phonon implementation that extracts ionic forces to calculate the temperature dependence of the phonon spectra. Scientists then applied the code to lead telluride (PbTe), a promising thermoelectric semiconductor material whose thermoelectric response has not yet been completely described. The completed version of the code for non-adiabatic phonon dispersion calculations and anharmonic thermal effects within a material is expected within the next few months. Along the way, researchers developed strong ties and a collaborative network with other institutions in Europe to produce future joint proposals of value.

Thermoelectric materials are the subject of extensive investigation for applications ranging from large-scale buildings to small-scale individual microelectronic components. Characterising their response properties is critical to advancements in the field to optimise cost-effectiveness and sustainability. NON ADIABATIC PHONON has made a major contribution to this effort with modelling code and numerical methods to describe novel behaviours.