Generic semiclassical transport simulator for new generation thermoelectric materials

Project Information

GENESIS

Grant agreement ID: 788465

DOI

10.3030/788465

Project closed

EC signature date 10 April 2018

Start date 2 July 2018

End date 1 July 2020

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 195 454,80

EU contribution

€ 195 454,80

Coordinated by

UNIVERSITY OF WARWICK
United Kingdom

Periodic Reporting for period 1 - GENESIS (Generic semiclassical transport simulator for new generation thermoelectric materials)

Reporting period: 2018-07-02 to 2020-07-01

Summary of the context and overall objectives of the project

One of the main challenges of our society is the energy sustainability and the impact of fossil fuels on the environment. Thermoelectric (TE) generators convert heat into electricity and provide energy savings and environmental sustainability. Currently, TE materials find use only in niche applications for reasons of low efficiency and high prices.
A big challenge in the TE research and industry is the identification and design of optimal materials. Simulations can provide accurate predictions to make materials design inexpensive and targeted. However, the calculation of the transport coefficients is in most cases performed in a very simplified way. Accurate transport simulators, easily adaptable to the generic bandstructure details of different materials, and robust enough to be attractive to experimentalists, are currently not available.
This project faces this challenge by constructing a robust simulator that can compute the TE properties of arbitrary materials by using as input their electron and phonon bandstructures. This will support the TE community in materials ranking, understanding of measurements, enabling time and cost reductions, which will accelerate the experimental efforts.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The achieved results involve three main areas:

1. Simulator development
The chosen language is MATLAB® that offers a robust and simple calculation environment, and compatibility with software used by the industry. After robust validation, the generation of C++ portable code, to speed up the code, is under development.
The approach has been set and validated versus experimentally assessed material systems: Si, Ge, GaAs, SiGe alloys. Then, the simulator has been enriched to consider the bipolar effects, important in narrow gap materials or at higher temperatures.
The simulator can account for the full numerical treatment of the following scattering mechanisms for the charge carriers: acoustic phonons, non-polar optical phonons, polar optical phonons, ionized impurities (dopants), alloy. For all of them except the alloy scattering, intra- and inter- valley options are available for the user, with the possibility to account for different parameters for different pairs of initial and final bands, and several optical phonon mechanisms can be included.
Several modules have been implemented to improve the user-friendliness of the simulator, and its use in supercomputing facilities. A Graphical User Interfaces (GUI) for the Input instructions, the scattering file preparation, and the data plot and conversion into .csv files have been developed as well.
A direct interface to the .bsxf files outputted by the XCrysden code has been developed, this allows to interface with some widely used DFT codes (Quantum ESPRESSO, CRYSTAL, WIEN2k). Interfaces with other DFT codes are under development.
The simulator has been applied to the case study of half-Heuslers, one of the most promising and studied class of TE materials. The main scientific results include:
- Demonstration of the importance of the proper treatment of the scattering physics in the materials ranking and best doping evaluation.
- Identification of the materials descriptors that drive TE performances.
- Observation of the unexpected high power factors in narrow bandgap semiconductors.

2. Networking
This activity aimed to enlarge the scientific network of the Experienced Researcher, promote his reputation in the community, advertise the simulator. The networking involved:
- Invited seminar, Univ. of York, 30 Aug. 2018
- Invited seminar, CNR, Chieti, 19 Feb. 2019
- GiTe2019, Bologna, 20-21 Feb. 2019
- MRS - Spring Meeting, Phoenix, AZ, 22-26 Apr. 2019
- IWCN - International Workshop of Computational Nanotechnology, Evanston, IL, 20-24 May 2019
- ECT , Cyprus, 23-25 Sept. 2019
- New Horizons in Materials Modelling, York, 10 Jan. 2020 (with side meetings for feedback in the development of the code attended by the PI, Fellow and faculty at York)
- APS – March Meeting, 2-6 March 2020, uploaded presentation (meeting cancelled for COVID-19).
- VCT – Virtual Conference on Thermoelectrics, 21-23 July 2020, substituting the International Conference on Thermoelectrics (ICT) that should have been hold in Seattle.
The simulator raised interest, especially the part related to the electronic transport properties, which is the first of its kind.

3. Exploitation, dissemination, public engagement
These activities include publications in international peer-reviewed journals, presentations at international conferences, workshops, and public engagement initiatives, code release.
Publications
- “Impact of the scattering physics on the power factor of complex thermoelectric materials”, J. Appl. Phys., 126, 155701 (2019).
- “Effective masses in complex band structures, a code to extract them”, arXiv preprint arXiv:1912.10924 (2019).
- “Material descriptors for the discovery of efficient thermoelectrics”, ACS Appl. Energy Mater. 3, 5913 (2020).
- “Ultra-High Thermoelectric Power Factors in Narrow Gap Materials with Asymmetric Bands”, J. Phys. Chem. C, DOI: 10.1021/acs.jpcc.0c05457 .
- “Carrier Scattering engineering in half Heusler thermoelectrics from first-principles”, in preparation.

Conferences and workshops
See Networking at point 2.

Public engagement:
- Science Festival in Cheltenham, 4-9 June 2019
- British Science Festival (Family Day), 14 Sept. 2019

Code release: The simulator is released open source under the GPL_v3 on the project web page at the University of Warwick and on the Psi-k platform. The essential documentation is provided. The code is planned to be released by September 2020.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Progress beyond the state-of-the-art
The simulator is beyond the state-of-the-art as there is no similar simulator in the community which considers the full energy/momentum/band dependence of scattering mechanisms. This enabled to achieve new knowledge about what drives the TE performance in advanced and/or complex materials. These results, presented in several conferences, raised deep interest and are being published.


Potential impacts, including socio-economic impact and the wider societal implications
The simulator will offer to the community a new, useful, yet missing, simulation tool for the charge transport TE coefficients. This will impact the computational work about the discovery of new TE materials by opening the possibility of accurate materials ranking and doping indications. This will also drive the experimental community towards the investigation of the most promising materials, accelerating the experimental discovery of new and efficient materials. In terms of promoting the ER’s scientific career, thanks to the results achieved during the project, the ER has been offered a permanent post at the CNR (National Research council, Italy).
In the long-term vision, we predict a profound implication in the realization of efficient TE generators and solar concentrators, with application in energy harvesting and clean energy production. This will have, in turn, great social impact in the energy sector.

Constant energy surfaces from TiCoSb valence band, presentation of material descriptors for the PF